JP6199062B2 - Display device and display method - Google Patents

Description

  The present invention relates to a display device and a display method.

  In recent years, thin, lightweight, and low power consumption display devices typified by liquid crystal display devices have become extremely popular. A typical mounting form of such a display device is, for example, a mobile phone, a smartphone, a notebook PC (Personal Computer), or the like. In the future, electronic paper, which is a thinner display device, is expected to develop and spread rapidly. Under such circumstances, it is a common problem to reduce power consumption in various display devices.

  In a conventional CG (Continuous Grain) silicon TFT liquid crystal display panel, an amorphous silicon TFT liquid crystal display panel, or the like, it is necessary to refresh the screen at 60 Hz. Therefore, attempts have been made to realize a refresh rate lower than 60 Hz in order to save power in the conventional liquid crystal display panel.

  Patent Document 1 describes a liquid crystal display in which when a stripe does not exist in an image over a series of frames, it is determined that the frame does not have a feature that easily causes flicker, and the refresh rate is reduced.

JP 2009-251607 A (released on October 29, 2009)

  However, in a liquid crystal display panel using CG silicon TFTs or amorphous silicon TFTs, the refresh rate can only be reduced to 50 Hz at most in order to maintain display quality.

  In recent years, development of an oxide semiconductor liquid crystal display panel in which a TFT is formed of an oxide semiconductor using indium (In), gallium (Ga), and zinc (Zn) has been intensively advanced. In a TFT formed using an oxide semiconductor, current leakage in an off state is small. Therefore, in the oxide semiconductor liquid crystal display panel, it is not necessary to refresh the screen at 60 Hz as in the conventional case, and the refresh rate can be reduced to about 1 Hz. Therefore, power consumption can be reduced.

  However, when the response speed of the liquid crystal is slow, there is a case where flicker is easily recognized when the display device is driven at a low refresh rate because the pixel capacity is not uniform. When the response speed of the liquid crystal is slow, the alignment state of the liquid crystal changes over a period when the liquid crystal is not refreshed. In addition, since charge leaks from the pixel through the TFT in the off state, when the pixel capacitance is not uniform, the change in the pixel potential varies from pixel to pixel.

  Patent Document 1 discloses a technique related to refresh rate setting. However, with this technique, it is not possible to sufficiently reduce power consumption and suppress flicker.

  According to one embodiment of the present invention, a display device that reduces power consumption and performs favorable display can be realized.

  A display device according to an aspect of the present invention includes a first pixel that displays a certain color in a first pixel and a second pixel that displays the color in a second pixel adjacent to the first pixel. A display panel, an image determination unit that determines whether or not an image indicated by display data in a certain period is an image having a feature that makes flicker easily visible, and an image in the period that has no feature that makes the flicker easy to see. If it is determined, the image is displayed by the first display method during the period. On the other hand, if it is determined that the image during the period has a feature that allows flicker to be visually recognized, the image is displayed by the second display method during the period. In the first display method, the gray level of the display data corresponding to the first pixel and the table corresponding to the second pixel are displayed. When the gradation of data is the same, the same potential is written to the first pixel and the second pixel, while in the second display method, the gradation of the display data corresponding to the first pixel and the second pixel are written. Even when the gradation of the display data corresponding to two pixels is the same, a pixel writing unit for writing different potentials to the first pixel and the second pixel is provided.

  A display method according to an aspect of the present invention is a display method of a display device, and the display device includes a first pixel that displays a certain color in the first pixel and a second pixel adjacent to the first pixel. An image determination step of determining whether or not an image indicated by display data in a certain period is an image having a characteristic that makes flickering easily visible, including a display panel including a second pixel that displays the color in the picture element; When it is determined that the image in the period does not have a feature that makes flicker easily visible, the image is displayed in the first display method in the period, while the image in the period has a feature that makes flicker easy to see. When the determination is made, the display method switching step for switching the display method so that the image is displayed in the second display method in the period, and the first pixel in the first display method. When the gradation of the corresponding display data and the gradation of the display data corresponding to the second pixel are the same, the same potential is written to the first pixel and the second pixel, while the second display method Then, even if the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same, the first pixel and the second pixel And a pixel writing step of writing different potentials.

  According to one embodiment of the present invention, a display device that suppresses power consumption and performs favorable display can be realized.

It is a block diagram which shows the structure of the display apparatus which concerns on one Embodiment of this invention. It is a graph which shows the flicker rate of each gradation when an oxide semiconductor liquid crystal display panel is driven with the refresh rate of 1 Hz. It is a timing chart when displaying a still image in the said display apparatus. It is a timing chart when displaying a moving image in the said display apparatus. It is a figure which shows the flowchart in which the host control part of the said display apparatus determines a display system. It is a figure which shows the state of the display part of the said display apparatus in column inversion drive. It is a figure which shows the state of the display part of the said display apparatus in dot inversion drive. It is a figure which shows the luminance characteristic (gradation-luminance characteristic) of the pixel with respect to the gradation of display data. It is a figure which shows the luminance characteristic (gradation-luminance characteristic) of the pixel with respect to the gradation of display data. It is a block diagram which shows the structure of the display apparatus which concerns on other embodiment of this invention. (A) shows the change of the gradation of the display data by the pseudo dot inversion processing of the display device, and (b) shows the change of the luminance rate of the corresponding pixel. It is a figure which shows the state of the display part of the said display apparatus in a 1st display system (without pseudo dot inversion process). It is a figure which shows the state of the display part of the said display apparatus in a 2nd display system (with pseudo dot inversion process). It is a figure which shows the flowchart which determines a display system in further another embodiment of this invention. (A) And (b) is a figure which shows the example of the image (still image) displayed on the screen of a display apparatus. It is a figure which shows the flowchart which determines a display system in further another embodiment of this invention. It is a figure which shows the screen of the said display apparatus. It is a figure which shows the screen of the said display apparatus. (A) is a figure which shows a predetermined pattern, (b) And (c) is a figure which shows the gradation map showing the gradation of each pixel of an image. It is a block diagram which shows the structure of the display apparatus which concerns on further another embodiment of this invention.

Embodiment 1
FIG. 2 is a graph showing the flicker rate of each gradation when the oxide semiconductor liquid crystal display panel is driven at a refresh rate of 1 Hz. The flicker rate represents the ease with which the flicker is visually recognized. The larger the value, the easier the flicker is visually recognized. For example, a flicker rate of 1.5% is one criterion for whether or not the flicker is easily visible. Whether or not flicker is likely to occur when driven at a low refresh rate depends on the gradation of the image to be displayed. In FIG. 2, the minimum gradation (black) is 0 and the maximum gradation (white) is 255. The ease with which the flicker is visually recognized also varies depending on the size of the screen and the manufacturing process. The panel 1 is a larger liquid crystal display panel than the panel 2. Panel 1 and panel 2 have different manufacturing processes.

  In the middle gradation, the response speed of the liquid crystal is relatively slow. In the intermediate gradation, a change in gradation (change in alignment of liquid crystal molecules) is likely to occur due to charge leakage through the TFT. Here, the intermediate gradation is a gradation excluding a saturation gradation (minimum gradation and maximum gradation). For example, when the minimum gradation is 0 and the maximum gradation is 255, the range from gradation 1 to gradation 254 is an intermediate gradation. In the case of normally black, flicker is more easily recognized in the range of gradation 10 to gradation 200, for example, among intermediate gradations. Further, the flicker is more easily recognized in the range from the gradation 20 to the gradation 80, and in particular, the flicker is easily recognized in the range from the gradation 40 to the gradation 60. For example, when an image including many pixels with gradations in the above range is displayed at a refresh rate of 1 Hz, the screen is refreshed every second, so the user may visually recognize flicker every second. is there.

  Therefore, in the present embodiment, when the image includes a large number of pixels in a predetermined range of gradation, that is, when the image has a feature that makes it easy to visually recognize flicker, the flicker is visually recognized by switching the display method. To prevent.

(Configuration of display device 1)
FIG. 1 is a block diagram showing a configuration of a display device according to an embodiment of the present invention. The display device 1 includes a display unit 10, a display drive unit 20, and a host control unit 30 (control device).

  The display unit 10 includes a screen, and is configured by, for example, an oxide semiconductor liquid crystal display panel as an active matrix type liquid crystal display panel. The oxide semiconductor liquid crystal display panel is a liquid crystal display panel in which the above-described oxide semiconductor-TFT is employed for a switching element provided corresponding to at least one of a plurality of pixels arranged two-dimensionally. . An oxide semiconductor-TFT is a TFT in which an oxide semiconductor is used for a semiconductor layer. As an oxide semiconductor, for example, an oxide semiconductor using an oxide of indium, gallium, and zinc (In—Ga—Zn—O) can be given. An oxide semiconductor-TFT has a large current flowing in an on state and a small leak current in an off state. Therefore, by employing an oxide semiconductor-TFT as the switching element, the pixel aperture ratio can be improved and the refresh rate of the screen display can be reduced to about 1 Hz. The reduction of the refresh rate brings about a power saving effect. The improvement in the pixel aperture ratio brings about an effect of brightening the display or a power saving effect by reducing the amount of light of the backlight when the display brightness is the same as that of the CG silicon liquid crystal display panel.

(Configuration of the host control unit 30)
The host control unit 30 includes a screen update detection unit 31 (update detection unit), a CPU 32, a host memory 33, a host TG 34 (host timing generator), an image determination unit 35, a display method switching unit 36, and a gamma correction unit 37. Yes. The host control unit 30 is configured by a control circuit formed on a substrate, for example.

  The screen update detection unit 31 detects whether it is necessary to update the display content of the screen of the display unit 10. For example, when an application that is activated and executed in the display device 1 notifies the screen update detection unit 31 of an update of the display content, the user of the display device 1 detects the update of the display content via the input unit. When notified to the unit 31, the screen update detecting unit 31 displays the screen display content to the CPU 32 when the screen update detecting unit 31 is notified of an update of the display content by data streaming or broadcast waves via the Internet. Notify that (image) needs to be updated.

  Here, the display data input to the screen update detection unit 31 includes an image of a frame whose display content is updated, and a display update flag (time reference) indicating the timing for displaying the image data. When the content of the image does not change over a plurality of frames, the data of the frame that does not change is not included in the display data. The screen update detection unit 31 can detect the necessity of updating the display content based on the display update flag. The screen update detection unit 31 stores the time of the frame when the content of the image has changed. Based on the display update flag, the screen update detection unit 31 detects an interval from a frame in which the content of the image has changed previously (from a frame in which the display content has been updated) to a frame in which the content of the image changes next. Whether the display is a moving image or a still image can be determined from the interval at which the content of the image changes. The screen update detection unit 31 outputs a display update flag and display data to the CPU 32. Further, the screen update detection unit 31 outputs an interval at which the content of the image changes to the display method switching unit 36.

  When the display update flag is not included in the display data input to the screen update detection unit 31 and all the frame data is included, the screen update detection unit 31 determines that the image of the previous frame By comparing with an image of a later frame, it can be determined whether or not the content of the image has changed. The screen update detection unit 31 can detect the necessity of updating the display contents from the comparison result. Also in this case, the screen update detection unit 31 detects the interval from the time of the updated frame until the next change of the image content after the change of the image content.

  The CPU 32 acquires display data for one screen from the screen update detection unit 31 and writes the display data to the host memory 33. In addition, the CPU 32 outputs display data to the image determination unit 35. The CPU 32 outputs an update flag to the host TG 34.

  The host memory 33 is a storage device configured by a VRAM (Video Random Access Memory) or the like.

  The image determination unit 35 determines whether or not the image indicated by the display data is an image (flicker image) having a feature that makes it easy to visually recognize flicker. Specifically, the image determination unit 35 determines whether or not each pixel in the image has a gradation in the range from the gradation 20 to the gradation 80 (second range). The image determination unit 35 obtains the ratio of pixels that are the gradation of the second range in a predetermined region of the image. Specifically, the image determination unit 35 generates a histogram in which a plurality of pixels are classified, for example, in increments of 10 gradations, and obtains the ratio of pixels that are gradations in the second range from the histogram. Here, the predetermined area is the entire image, but the predetermined area may be a partial area of the image. The image determination unit 35 determines whether or not the ratio of pixels that are gradations in the second range is 30% (first threshold) or more. When the ratio is 30% or more, the image determination unit 35 determines that the image has a characteristic that makes it easy to visually recognize flicker. When the ratio is less than 30%, the image easily causes the image to visually recognize flicker. It is determined that it does not have. The image determination unit 35 displays the determination result of whether or not the ratio of the pixels that are the gradations in the second range is equal to or greater than the first threshold (whether or not the image has a feature that makes it easy to visually recognize flicker). To the unit 36. The values such as the second range and the first threshold are examples, and other values may be used.

  The display method switching unit 36 switches the display method of the display unit 10 based on the determination result of the image determination unit 35. When it is determined that the display is a still image and the image does not have a feature that makes it easy to visually recognize flicker, the display method switching unit 36 determines to display the image by column inversion driving (first display method). To do. On the other hand, when it is determined that the display is a still image and the image has characteristics that make it easy to visually recognize flicker, the display method switching unit 36 displays the image by dot inversion driving (second display method). decide. However, when the display is a moving image, the display method switching unit 36 determines to display the image by column inversion driving regardless of the determination result of the image determination unit 35. Note that, regardless of whether the image is a still image or a moving image, the display method may be determined depending on whether the image has a feature that makes it easy to visually recognize flicker.

  Column inversion driving has the advantage of lower power consumption than dot inversion driving. On the other hand, the dot inversion drive has an advantage in that it consumes less power than the column inversion drive but is less likely to cause flicker. For this reason, when the image itself has a feature that makes it easy to visually recognize flicker, display is performed by dot inversion driving in order to suppress the occurrence of flicker. When the display is a moving image, the content of the image changes at short intervals. Therefore, even if the number of pixels in the second range is large, flicker is difficult to see. Therefore, when the display is a moving image, there is no need to perform dot inversion driving. The display method switching unit 36 can determine whether the display is a moving image or a still image from the interval at which the content of the image changes. The display method switching unit 36 instructs the display driving unit 20 to display the display method so that the display unit 10 is driven by the determined display method (column inversion driving or dot inversion driving). The display method switching unit 36 also instructs the gamma correction unit 37 to display the display method.

  The gamma correction unit 37 acquires display data from the host memory 33 and performs gamma correction on the display data using different parameters according to the display method instructed from the display method switching unit 36. Specifically, the gamma correction unit 37 includes a first LUT (lookup table) suitable for column inversion driving and a second LUT suitable for dot inversion driving. When the display method is column inversion driving, the gamma correction unit 37 performs gamma correction on the display data using the first LUT. When the display method is dot inversion driving, the gamma correction unit 37 performs gamma correction on the display data using the second LUT. The gamma correction unit 37 outputs the display data after the gamma correction to the host TG 34.

  When receiving the update flag from the CPU 32, the host TG 34 transfers the display data after the gamma correction acquired from the gamma correction unit 37 to the display driving unit 20. The host TG 34 transfers the display data of the updated frame image to the display drive unit 20 only when the display content (image) needs to be updated. The display data is transferred according to data communication specifications of mobile devices such as MIPI (Mobile Industry Processor Interface). The host TG 34 transfers a synchronization signal to the display driving unit 20 together with the display data after the gamma correction.

(Configuration of display driving unit 20)
The display drive unit 20 is, for example, a so-called COG driver mounted on a glass substrate of the display unit 10 by COG (Chip on Glass), and the display unit 10 is displayed on the screen so as to perform display based on display data. To drive. The display driving unit 20 includes a memory 21, a TG 22 (timing generator), and a source driver 23 (pixel writing unit).

  The memory 21 stores display data transferred from the host control unit 30. The memory 21 continues to hold display data until the next display update is performed (that is, as long as the content of the image does not change).

  The TG 22 generates a timing signal for driving the display unit 10. The TG 22 reads the display data from the memory 21 when the content of the image changes (that is, when the display data is transferred from the host control unit 30 to the display driving unit 20), and sends the timing signal and the display data to the source driver 23. Output. Further, the TG 22 reads display data from the memory 21 and outputs a timing signal and display data to the source driver 23 when a predetermined period has elapsed since the potential was written to the pixel of the display unit 10. For example, if the predetermined period is 1 second, the still image refresh rate is 1 Hz. If the predetermined period is 0.1 second, the still image refresh rate is 10 Hz. Further, when displaying a moving image, the refresh rate is adjusted to the frame rate of the moving image. For example, if the frame rate of the moving image is 30 Hz, the refresh rate is 30 Hz. Note that the TG 22 may use a synchronization signal input from the host TG to generate a timing signal.

  The source driver 23 writes the potential corresponding to the display data to the pixels of the display unit 10 in accordance with the timing signal in the display method instructed from the host control unit 30. Specifically, the source driver 23 generates a source signal having a potential corresponding to the gradation indicated by the display data after the gamma correction, and supplies the source signal to the pixels of the display unit 10. In order to drive the display unit 10 by column inversion driving or dot inversion driving, the source driver 23 inverts the polarity of the potential of the source signal supplied to each pixel for each frame in which writing is performed. In column inversion driving (first display method), the polarity of the potential written to each pixel in one frame is inverted for each column (pixel column or pixel column). In dot inversion driving (second display method), the polarity of the potential written to each pixel in one frame is inverted for each column and each row. Here, the polarity is + if it is higher than the potential of the common electrode provided in the display panel, and the polarity is-if it is lower than the potential of the common electrode.

  In addition, as a suitable example of the display device 1, for example, a mobile phone, a smartphone, a notebook PC, a tablet terminal, an electronic book reader, a PDA, or the like can be given a display device that places particular emphasis on portability.

(Display drive method)
FIG. 3 is a timing chart when a still image is displayed on the display device 1. FIG. 3 shows a case where still image A and still image B are displayed in order. The image A is an image that does not have a feature in which flicker is easy to visually recognize because the proportion of pixels in the second range (gradation 20 to gradation 80) is smaller than the first threshold (30%). The image B is an image having a feature in which the ratio of pixels in the second range of gradations is equal to or greater than the first threshold and the flicker is easily visible. Therefore, the image A is displayed by column inversion driving, and the image B is displayed by dot inversion driving.

  As shown in FIG. 3A, only when the content of the image changes, the display data (image A, image B) for one screen (after gamma correction) is sent from the host control unit 30 to the display driving unit 20. Transferred. After the display data of the image A is transferred, the display data is transferred from the host control unit 30 to the display driving unit 20 when the display content is updated to the image B.

  The display drive unit 20 stores the received display data (image A) in the memory 21 and updates the display on the display unit 10 to the image A at a timing synchronized with the driver internal vertical synchronization signal of FIG. ((C) of FIG. 3). The driver internal vertical synchronization signal is generated by the TG 22 every predetermined period (1 second). Note that the delay time from when the display driving unit 20 receives the display data until it is displayed is omitted here. The dotted pulse indicates that no vertical sync signal has been generated there.

  Thereafter, the display refresh of the image A is performed every second (at 1 Hz). In the display drive unit 20, the TG 22 reads display data (image A) from the memory 21 every second, and the source driver 23 supplies the display unit 10 with a potential corresponding to the display data.

  When receiving the display data indicating the image B, the display driving unit 20 updates the display on the display unit 10 to the image B regardless of the refresh rate. Thereafter, the display refresh of the image B is performed every second. In the display drive unit 20, the TG 22 reads display data (image B) from the memory 21 every second, and the source driver 23 supplies a potential corresponding to the display data to the display unit 10. At this time, the driver internal vertical synchronization signal is also generated in accordance with the refresh rate of 1 Hz.

  FIG. 4 is a timing chart when a moving image is displayed on the display device 1. FIG. 4 shows a case where images A to E, which are moving images, are displayed in order. Images A, B, D, and E are each displayed for 1/30 seconds, and image C is displayed for 1/15 seconds. The interval at which the content of the image changes is equal to or less than the interval threshold (for example, 400 ms) in any of images A to E. Therefore, since the images A to E are determined to be moving images, the images A to E are displayed by column inversion driving regardless of the gradation of the image.

  As shown in FIGS. 4 (a) and 4 (b), only when the content of the image has changed, the host controller 30 sends the display driver 20 for one screen at a timing synchronized with the vertical synchronization signal (transfer). Display data (image A to image E) after gamma correction is transferred.

  The display drive unit 20 stores the received display data (image A) in the memory 21 and updates the display on the display unit 10 to the image A at a timing synchronized with the driver internal vertical synchronization signal of FIG. ((D) of FIG. 4). The driver internal vertical synchronization signal is generated by the TG 22 according to the timing of receiving display data from the host control unit 30.

(Display method decision flow 1)
FIG. 5 is a flowchart illustrating how the host control unit 30 determines the display method. Each time the screen update detection unit 31 detects a display update (change in image content), the flow of FIG. 5 is executed.

  When the screen update detection unit 31 detects a change in the image content from the display update flag or the like, the screen update detection unit 31 detects an interval at which the image content changes. The display method switching unit 36 determines whether or not the interval at which the content of the image changes (update interval) is equal to or less than a predetermined interval threshold (for example, 400 ms) (S1).

  When the interval at which the content of the image changes is equal to or smaller than the interval threshold (Yes in S1), the display method switching unit 36 determines that the displayed image is a moving image, and determines the display method to be column inversion driving (S2). ).

  When the interval at which the content of the image changes is larger than the interval threshold (No in S1), the display method switching unit 36 determines that the displayed image is a still image. The image determination unit 35 obtains the ratio of pixels that are in the second range (the range from the gradation 20 to the gradation 80) in the entire image. Then, the image determination unit 35 determines whether or not the ratio of the pixels having the gradation in the second range is equal to or greater than the first threshold (30%) (S3).

  When the interval at which the content of the image changes is greater than the interval threshold and the ratio of pixels that are in the second range of gradation is less than the first threshold (30%) (No in S3), the display method switching unit 36 The display method is determined to be column inversion driving (S4).

  When the interval at which the content of the image changes is greater than the interval threshold and the proportion of pixels that are in the second range of gradation is equal to or greater than the first threshold (30%) (Yes in S3), the display method switching unit 36 The display method is determined to be dot inversion driving (S5).

(Write to display unit 10)
FIG. 6 is a diagram illustrating a state of the display unit 10 in the column inversion driving. FIG. 7 is a diagram illustrating a state of the display unit 10 in dot inversion driving. The display unit 10 includes pixels PIX corresponding to the three colors R (red), G (green), and B (blue). Each picture element PE includes three pixels PIX of RGB. The pixel electrode of each pixel PIX is opposed to a common electrode (not shown) across the liquid crystal. Each pixel PIX has a TFT in which an oxide semiconductor is used as a semiconductor layer of the TFT. “+” And “−” in FIGS. 6 and 7 indicate the polarities of the potentials written in the pixels PIX. Here, regarding the polarity of the potential, the potential of the common electrode is considered as a reference (0 V). The source signal line SL is arranged along the pixel column and supplies a source signal to the pixel PIX. The scanning signal line GL is arranged along the pixel row and controls conduction / non-conduction of the TFT of the pixel PIX. The picture element PE2 is a picture element adjacent to the picture element PE1 in the column direction. An R pixel included in the picture element PE1 is a pixel PIX1, and an R pixel included in the picture element PE2 is a pixel PIX2. The source driver 23 generates a source signal having a potential corresponding to each gradation from the display data of the digital gradation (after gamma correction), and supplies the source signal to the source signal line SL. At this time, the source driver 23 sets the polarity of the potential of the source signal according to whether it is column inversion driving or dot inversion driving.

  In the column inversion driving shown in FIG. 6, the polarity of the potential written to the pixel is inverted for each pixel column in one frame. Further, in the column inversion drive, the polarity of the potential written to each pixel is inverted every frame for writing. Note that the polarity of the potential written to the pixel may be reversed not for each pixel column but for each pixel column.

  In the dot inversion driving shown in FIG. 7, the polarity of the potential written to the pixel is inverted for each pixel column and pixel row in one frame. Therefore, in the dot inversion driving, the polarities of the potentials written in the pixels PIX1 and PIX2 adjacent in the pixel column direction are different, and the polarities of the potentials written in the pixels PIX1 and PIX5 adjacent in the pixel row direction are also different. Further, in the dot inversion driving, the polarity of the potential written to each pixel is inverted every frame for writing. Note that the polarity of the potential written to the pixel may be reversed not for each pixel column and pixel row but for each pixel column and pixel row.

  Here, in the display data supplied from the application, a case where the gradation of the display data corresponding to the pixel PIX1 and the gradation of the display data corresponding to the pixel PIX2 are the same will be described. That is, in the display data, the gradation of red pixels adjacent in the column direction is the same. The gradation of the display data is subjected to gradation conversion (gamma correction) while being digital in the gamma correction unit 37. Since the gradation of the display data corresponding to the pixel PIX1 and the gradation of the display data corresponding to the pixel PIX2 are the same before the gamma correction, the gradations of both are the same after the gamma correction.

  In the column inversion drive, source signals having the same polarity are supplied to one pixel column. Therefore, if the gradation of the display data is the same, the pixels PIX1 and PIX2 adjacent in the column direction have the same potential ( For example, + 2V) is written. In the next frame, the same negative potential (for example, −2 V) is written in the pixels PIX1 and PIX2.

  On the other hand, in dot inversion driving, source signals having different polarities are supplied to two pixels PIX1 and PIX2 adjacent in the pixel column direction. For this reason, even if the gradation of the display data is the same, the potential written to the pixel PIX1 (for example, + 2V) and the potential written to the pixel PIX2 (for example, −2V) are different. However, although the two pixels PIX1 and PIX2 have different potential polarities, the voltage difference with respect to the potential (0 V) of the common electrode is substantially the same, so that the transmittance (that is, luminance) of the liquid crystal is substantially the same.

  Strictly speaking, there is a case where the positive polarity luminance and the negative polarity luminance do not coincide with each other because the potential of the common electrode is deviated from the positive and negative central potential (0 V). In the case of the column inversion driving, the luminance difference is different for each column, so that the flicker of the column pattern is easily visually recognized. On the other hand, in the dot inversion driving, the positive polarity and the negative polarity of the pixels are distributed in a checkered pattern, so that the flicker is hardly visually recognized.

(Gamma correction)
The gamma correction of this embodiment will be described in more detail. The gamma correction unit 37 performs different gamma corrections depending on whether column inversion driving or dot inversion driving is performed.

  FIG. 8 is a diagram illustrating the luminance characteristics (gradation-luminance characteristics) of the pixels with respect to the gradation of the display data. In FIG. 8, the vertical axis represents the luminance rate (that is, the transmittance), and the maximum luminance is 100 (%). The horizontal axis represents the gradation of display data before gamma correction (any gradation of RGB), and its range is from 0 to 255. In the display device 1, with respect to the gradation of the display data supplied from the application or the like, the luminance of the pixel has a gamma characteristic (gradation-luminance characteristic: gamma value 2.2) as shown in FIG. Perform gamma correction on the display data. For example, in the case of performing display by column inversion driving, the gamma correction unit 37 converts the gradation (input gradation) of the display data of gradation 60 into gradation 50 (output gradation), and performs gamma correction. Output as display data.

  However, even if the gradation of the display data after the gamma correction is the same, the gamma characteristics appear different between the column inversion driving and the dot inversion driving. If the gamma correction is performed with the same γ parameter as in the column inversion driving also in the dot inversion driving, the actual luminance becomes a gamma characteristic different from that in FIG. 8, for example, as shown in FIG. This is because in the dot inversion driving, the polarity of the source signal line is inverted every horizontal period, so that the source signal line needs to be charged.

  Therefore, the gamma correction unit 37 performs gamma correction using a γ parameter (different LUT) different from that for the column inversion drive when performing display by dot inversion drive. For example, when performing display by dot inversion driving, the gamma correction unit 37 converts the gradation (input gradation) of the display data of gradation 60 to gradation 55 (output gradation), and performs gamma correction. Output as display data. As described above, the gamma correction unit 37 has the first range of gradations in which the gradation of the display data (input gradation) is the intermediate gradation (the gradation in the range where the gamma characteristic appears to change: for example, gradation 10 To 250, the output gradation after gamma correction is converted into different gradations in column inversion driving and dot inversion driving. Therefore, when the gray level of the display data corresponding to a certain pixel PIX is in the first range, for example, a source signal of +2 V is supplied to the pixel PIX in the column inversion driving, and the pixel PIX in the dot inversion driving, for example. Are supplied with a +2.1 V source signal having the same polarity and different potential. Even in this case, the potential of the pixel as a result of writing is almost the same between the column inversion driving and the dot inversion driving. As described above, by performing different gamma corrections in the column inversion driving and the dot inversion driving, the gradation-luminance characteristics by the column inversion driving and the gradation-luminance characteristics by the dot inversion driving become the same (both in FIG. 8). become that way).

(Effect of display device 1)
According to the display device 1 of the present embodiment, when displaying an image in which flicker is easily visible in displaying a still image, it is possible to prevent the flicker from being visually recognized by changing the display method to dot inversion driving. it can. Further, in displaying a still image, when displaying an image in which flicker is difficult to visually recognize, power consumption can be reduced by setting the display method to column inversion driving. The display device 1 displays at a refresh rate that matches the update frequency of the moving image when displaying a moving image, and displays at a lower refresh rate (for example, 10 Hz or less) when displaying a still image. Therefore, the display device 1 can reduce power consumption while maintaining high display quality.

  In the display of moving images, flicker is difficult to be visually recognized regardless of the gradation of the image. Therefore, when displaying a moving image, the display device 1 reduces power consumption by changing the display method to column inversion driving. It should be noted that the refresh rate for displaying a moving image may be at least the updating frequency of the moving image.

  In the display device 1, the refresh operation is performed by the display drive unit 20 during a period in which the image content does not change, and the host control unit 30 does not need to transfer the image to the display drive unit 20. Therefore, the operation of the host control unit 30 can be paused during a period in which the image does not change. The power saving effect due to the suspension of the host control unit 30 is very large.

(Modification 1)
One picture element includes RGB pixels. In the above example, the image determination unit 35 determines the ratio of pixels that are gradations in the second range in the image regardless of the color (RGB) of the pixels.

  On the other hand, the image determination unit 35 may obtain a ratio of pixels that are gradations in the second range for each RGB, and weight the ratio for each color. In this case, the image determination unit 35 determines whether or not the total value obtained by weighting the ratio for each color is equal to or greater than a predetermined threshold value. Generally, it is said that the strength of recognition of human RGB is R: G: B = 3: 6: 1. That is, since a human recognizes G (green) pixels strongly, flicker is likely to be visually recognized if the G pixels have many gradations in the second range. Therefore, the image determination unit 35 has a ratio Rr of R pixels that are gradations of the second range of R (red) pixels and a gradation of the second range of G pixels in a predetermined region of the image. The ratio Rg of the G pixel and the ratio Rb of the B pixel that is the gradation of the second range among the B pixels are obtained. The image determination unit 35 obtains (3 × Rr) + (6 × Rg) + (1 × Rb) as a weighted total value. If the total value is equal to or greater than a predetermined threshold (for example, (3 + 6 + 1) × 30 [%]), the image determination unit 35 can determine that the image is an image in which flicker is easily visible.

  The image determination unit 35 may determine whether or not the image has an easy-to-view flicker characteristic based on the luminance Y of the picture element obtained from the RGB gradation. For each picture element, the image determination unit 35 obtains the luminance Y as, for example, luminance Y = R gradation × 0.29891 + G gradation × 0.58661 + B gradation × 0.11448. If the luminance Y of the picture element is within a predetermined range (for example, 20 to 80), the image determination unit 35 determines that the plurality of pixels included in the picture element are in the second range of gradation. Good. In other words, if the proportion of picture elements whose luminance Y is within a predetermined range is equal to or higher than the first threshold (30%), display is performed by the second display method (dot inversion driving) in order to prevent flicker from being visually recognized. Is called. In this case, the image determination unit 35 only needs to store a histogram for the luminance Y of each picture element, so that the storage capacity is only about 1/3 as compared with the case of storing a histogram for the gradation of each pixel.

[Embodiment 2]
Still another embodiment of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In this embodiment, the image determination unit and the display method switching unit are provided on a substrate other than the host control unit. In this embodiment, in order to prevent flicker from being visually recognized, display is performed by a pseudo dot inversion technique using image processing instead of dot inversion driving.

(Configuration of display device 2)
FIG. 10 is a block diagram showing the configuration of the display device of this embodiment. The display device 2 includes a display unit 10, a display drive unit 40, a display control unit 50 (control device), and a host control unit 60.

  Similar to the first embodiment, the display driving unit 40 is a COG driver that is COG-mounted on the glass substrate of the display unit 10, and drives the display unit 10. The host control unit 60 is a control board configured by a control circuit formed on the substrate, and mainly takes control of the host side of the display device 2. The display control unit 50 is a control board provided separately from the host control unit 60 for image processing or the like for an image to be displayed. In the present embodiment, the display control unit 50 performs display method determination and image processing according to the display method. Thereby, it is possible to reduce the load on the host control unit 60 and to secure the processing capability for causing the host control unit 60 to perform another process other than the display.

  The display driving unit 40 includes a source driver 23. In the present embodiment, the source driver 23 can handle only column inversion driving and does not perform dot inversion driving. In the present embodiment, display is always performed by column inversion driving.

(Configuration of host control unit 60)
The host control unit 60 includes a screen update detection unit 61, a CPU 62, a host memory 33, and a host TG 34.

  The screen update detection unit 61 may detect the interval at which the content of the image changes and notify the display control unit 50, or may not detect the interval at which the content of the image changes. For example, the interval at which the content of the image changes may be detected on the display control unit 50 side. For other points, the screen update detection unit 61 performs the same processing as the screen update detection unit 31 of the first embodiment.

  The CPU 62 performs the same processing as the CPU 32 of the first embodiment except that display data is not output to the image determination unit.

  The host TG 34 transfers the display data of the updated image to the display control unit 50 only when the display needs to be updated.

(Configuration of display control unit 50)
The display control unit 50 includes an image processing unit 51, an image determination unit 52, a display method switching unit 53, a memory 21, and a TG 22.

  When the display data is received from the host control unit 60, the image determination unit 52 determines whether or not the image indicated by the display data is an image having characteristics that make it easy to visually recognize flicker. The determination process of the image determination unit 52 is as described in the above embodiment. The image determination unit 52 outputs the determination result to the display method switching unit 53. Further, the image determination unit 52 (update detection unit) can detect an interval at which the image changes, and output the interval at which the image changes to the display method switching unit 53.

  The display method switching unit 53 determines the display method based on the determination result of the image determination unit 52. When the image determination unit 52 determines that the image does not have a feature that makes it easy to visually recognize flicker, the display method switching unit 53 determines to display the image in the first display method during the period during which the image is displayed. On the other hand, when the image determination unit 52 determines that the image has a feature that makes it easy to visually recognize flicker, the display method switching unit 53 determines to display the image in the second display method during the period in which the image is displayed. In the present embodiment, the first display method is a display method that does not perform pseudo dot inversion processing, and the second display method is a display method that performs pseudo dot inversion processing. The display method switching unit 53 instructs the image processing unit 51 to select a display method so that image processing according to the determined display method is performed.

  The image processing unit 51 performs pseudo dot inversion processing (image processing) on the display data received from the host control unit 60 according to the display method. In the first display method, the image processing unit 51 does not perform pseudo dot inversion processing. In the second display method, the image processing unit 51 performs pseudo dot inversion processing.

  The second display method (pseudo dot inversion process) will be described. The image processing unit 51 performs predetermined processing such that the gradation of display data corresponding to a plurality of pixels is the same and the gradation of the second range (range of gradations 20 to 80) for each RGB color. An area larger than the size of is detected. The area where the pixels of the second range of gradations are gathered in a predetermined size or more is an area where flicker is easily visible. The image processing unit 51 converts the detected area (target area) into display data so that the gradation in the target area is discontinuous in the row direction and the column direction as in a checkered pattern. On the other hand, image processing (pseudo dot inversion processing) is performed.

  FIG. 11A shows the change in the gradation of the display data due to the pseudo dot inversion process, and FIG. 11B shows the change in the luminance rate of the corresponding pixel. In FIG. 11, attention is paid only to the R pixel. In the display data, the gradation of the R pixel in the target area is assumed to be 50. When the gradation of the display data is 50, if the pseudo dot inversion process is not performed on the display data, the luminance rate (or transmittance) of the corresponding pixel is 10%. The luminance rate is a luminance ratio (%) when the minimum luminance is 0% and the maximum luminance is 100%.

  In the pseudo dot inversion processing, processing such as dithering or error diffusion is performed on the target area in the display data, and image processing is performed so that the gradation values are arranged in a checkered pattern. For example, when the gray level in the target area of the display data is 50, the gray level corresponding to the pixel PIX1 is converted to high for the target area, and the gray level corresponding to the pixel PIX2 adjacent to the pixel PIX1 is converted to low. When the pseudo dot inversion process is performed, bright pixels (pixel PIX1) having a luminance rate of 20% and dark pixels (pixel PIX2) having a luminance rate of 0% are arranged in a checkered pattern. At this time, in the display data after the pseudo dot inversion process (after conversion), pixels of gradation 130 corresponding to a luminance rate of 20% and pixels of gradation 0 corresponding to a luminance rate of 0% are arranged in a checkered pattern. When the pseudo dot inversion process is performed, the average luminance rate in the target area is 10%. Thus, when the display data pseudo-dot inversion processing is performed (second display method), the luminance of the pixel PIX1 and the average luminance of the pixel PIX2, and when the display data pseudo-dot inversion processing is not performed (first display method) Gradation conversion (image processing) is performed so that the luminance of the pixel PIX1 is the same. Here, the case where the gradation of the target area in the display data is uniform has been described. However, even if the gradation of the target area is slightly different, such as gradation, the average luminance of the target area before conversion and the post-conversion The gradation conversion may be performed so that the average luminance of the target area is the same and the gradation distribution (brightness / darkness distribution) is a checkered pattern (dither pattern).

Note that the image processing unit 51 may apply the pseudo dot inversion process only to a partial region of the image. For example, if flicker is conspicuous in the central part of the screen due to the characteristics of the display device, if there is a target area where it is easy to visually recognize flicker in the central part of the image, pseudo dot inversion processing is performed on the target area. It can also be set as the structure to perform.
The image processing unit 51 can also perform other image processing such as color adjustment prior to the pseudo dot inversion processing. The image processing unit 51 performs predetermined gamma correction (for column inversion driving) after the pseudo dot inversion processing. The image processing unit 51 writes display data subjected to image processing into the memory 21.

  The configuration of the TG 22 is the same as that of the first embodiment. The TG 22 reads display data from the memory 21 and transfers the display data to the source driver 23 of the display driving unit 40.

(Write to display unit 10)
FIG. 12 is a diagram illustrating a state of the display unit 10 in the first display method (without pseudo dot inversion processing). FIG. 13 is a diagram illustrating a state of the display unit 10 in the second display method (with pseudo dot inversion processing). The picture element PE2 is a picture element adjacent to the picture element PE1 in the column direction. The picture element PE3 is a picture element adjacent to the picture element PE1 in the row direction. The picture element PE4 is a picture element adjacent to the picture element PE3 in the column direction. The R pixel included in the picture element PE1 is referred to as a pixel PIX1, the R pixel included in the picture element PE2 is referred to as a pixel PIX2, the R pixel included in the picture element PE3 is referred to as a pixel PIX3, and the R pixel included in the picture element PE4 is referred to as a pixel PIX4. In this embodiment, display is performed by column inversion driving regardless of the display method.

  Here, a case will be described in which display data supplied from an application has the same gradation of display data corresponding to the pixels PIX1 to PIX4. That is, in the display data, the gradation of 2 × 2 red pixels is the same.

  In the first display method shown in FIG. 12, since the pseudo dot inversion process is not performed, if the display data has the same gradation, the pixel PIX1 and the pixel PIX2 in one column have positive polarity corresponding to the gradation 50. Are written in the same potential (for example, +1.6 V), and the same negative polarity potential (for example, −1.6 V) corresponding to the gradation 50 is written in the pixels PIX3 and PIX4 in the other column. In the next frame, the same negative potential (for example, −1.6 V) is written in the pixel PIX1 and the pixel PIX2, and the same positive potential (for example, +1.6 V) is written in the pixel PIX3 and the pixel PIX4. ) Is written.

  On the other hand, in the second display method shown in FIG. 13, since the pseudo dot inversion process is performed, even if the display data has the same gradation, the pixel PIX1 has a positive potential corresponding to the gradation 130 (for example, +2. 2V) is written, and a positive potential (for example, +0.1 V) corresponding to the gradation 0 is written in the pixel PIX2 adjacent in the column direction. Further, a negative potential (for example, −0.1 V) corresponding to the gradation 0 is written in the pixel PIX3, and a negative potential (for example, −2) corresponding to the gradation 130 is written in the pixel PIX4 adjacent in the column direction. .2V) is written. As described above, in the second display method, different potentials are written to adjacent pixels even if the gradation of the display data is the same.

(Effect of display device 2)
As described above, the image processing unit 51 converts the gradations of a plurality of pixels that are in the second range (range of gradations 20 to 80) in the display data into bright gradations (gradations 81 to 255) outside the second range. And it converts to dark gradation (gradation 0 to 19). As a result, the number of pixels in the second range of gradation in which flicker is easily visible can be reduced. In addition, the average luminance of the area where the gradation is converted is the same as the average luminance before conversion. Therefore, it appears to the user that the same image as in the first display method is displayed even if the display is performed in the second display method. Therefore, the display device 2 can prevent flicker from being visually recognized while maintaining the display quality of the image.

  Further, if image processing is performed, power consumption increases. The display device 2 performs the pseudo dot inversion process only when it is determined that the image is easy to visually recognize flicker. Further, since the display device 2 prevents flicker from being visually recognized by image processing, it is not necessary to perform dot inversion driving with high power consumption. Therefore, the display device 2 can suppress increase in power consumption and prevent flicker from being visually recognized.

  Note that the image processing unit 51, the image determination unit 52, and the display method switching unit 53 that perform the pseudo dot inversion processing described in the present embodiment may be provided in the host control unit as in the first embodiment. Further, the image determination unit 35, the display method switching unit 36 for switching the inversion driving method, and the gamma correction unit 37 of the first embodiment may be provided in the display control unit as in the present embodiment.

  In the above example, the gradations of a plurality of pixels that are in the second range (the range of gradations 20 to 80) in the display data are set to bright gradations (gradations 81 to 255) that are outside the second range and dark levels. Although an example of conversion to a tone (gradation 0 to 19) is shown, all pixels in the second range of gradations may not be strictly eliminated. By distributing pixels of flicker gradation (gradation in which flicker is easily visible), there is an effect that flicker is less visible.

[Embodiment 3]
Another embodiment of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the block configuration of the display device is the same as in the first or second embodiment, but the display method determination flow is different from that in the above-described embodiment. The display method determination flow described here is applicable to both the first and second embodiments.

(Display method decision flow 2)
FIG. 14 is a diagram showing a flowchart for determining a display method in the present embodiment. The flow shown in FIG. 14 is executed each time the screen update detection units 31 and 61 (FIG. 1 or FIG. 10) detect display updates (changes in image contents).

  When the screen update detector 31 or 61 detects a change in the content of the image from the display update flag or the like, it detects an interval at which the content of the image changes. In addition, the image determination units 35 and 52 generate a histogram that classifies each pixel of the image using gradation as a bin. The display method switching units 36 and 53 determine whether or not the interval at which the image content changes (update interval) is equal to or smaller than a predetermined interval threshold (S11).

  When the interval at which the content of the image changes is larger than the interval threshold (No in S11), the display method switching unit determines that the displayed image is a still image. The image determination unit determines whether or not the condition 1 is satisfied (S12). Condition 1 is that the ratio of pixels in the second range (range of gradations 20 to 80) in the entire image is greater than or equal to the first threshold (30%).

  When the interval at which the content of the image changes is larger than the interval threshold and satisfies the condition 1 (Yes in S12), the display method switching unit uses the second display method (dot inversion driving or pseudo dot) that makes it difficult to visually recognize the flicker. It is determined that there is an inversion process (S13).

  When the interval at which the content of the image changes is larger than the interval threshold and the condition 1 is not satisfied (No in S12), the image determination unit determines whether the condition 2 is satisfied (S14). Condition 2 is that the ratio of pixels in the third range (the range of gradations 10 to 160) in the entire image is greater than or equal to the second threshold (50%).

  When the interval at which the content of the image changes is greater than the interval threshold, does not satisfy the condition 1, and satisfies the condition 2 (Yes in S14), the display method switching unit determines the display method as the second display method (S15). ). The third range includes the second range but is wider than the second range. A pixel having the gradation in the third range is less likely to cause flicker than a pixel having the gradation in the second range, but may cause slight flicker. Therefore, when the condition 2 is satisfied, display is performed in the second display method in order to prevent flicker from being visually recognized.

  When the interval at which the content of the image changes is greater than the interval threshold, does not satisfy the condition 1, and does not satisfy the condition 2 (No in S14), the display method switching unit changes the display method to the first display method with low power consumption. (No column inversion driving or pseudo dot inversion processing) is determined (S16). When neither condition 1 nor condition 2 is satisfied, it can be determined that flicker is not visually recognized even if display is performed in the first display method. Therefore, power consumption is reduced by performing display using the first display method.

  When the interval at which the content of the image changes is equal to or smaller than the interval threshold (Yes in S11), the display method switching unit determines that the displayed image is a moving image. The image determination unit determines whether or not the condition 3 is satisfied (S17). Condition 3 is that the ratio of pixels in the fourth range (the range of gradations 40 to 60) in the entire image is greater than or equal to the third threshold (40%). Here, the fourth range is included in the second range and is narrower than the second range.

  When the interval at which the content of the image changes is equal to or smaller than the interval threshold and satisfies the condition 3 (Yes in S17), the display method switching unit determines the display method to be the second display method (S18). Even in the case of a moving image, flicker may be visually recognized particularly when there are many pixels with gradations that are likely to cause flicker. Even in this case, it is possible to prevent the flicker from being visually recognized by performing display using the second display method.

  When the interval at which the content of the image changes is equal to or less than the interval threshold and does not satisfy the condition 3 (No in S17), the image determination unit determines whether the condition 4 is satisfied (S19). Condition 4 is that the ratio of pixels in the fifth range (the range of gradations 20 to 80) in the entire image is equal to or greater than the fourth threshold (60%).

  When the interval at which the content of the image changes is equal to or less than the interval threshold, and does not satisfy the condition 3 and satisfies the condition 4 (Yes in S19), the display method switching unit determines the display method to be the second display method ( S20). The fifth range includes the fourth range but is wider than the fourth range. Therefore, when the condition 4 is satisfied, display is performed by the second display method in order to prevent flicker from being visually recognized.

  When the interval at which the content of the image changes is equal to or smaller than the interval threshold value and does not satisfy condition 3 and does not satisfy condition 4 (No in S19), the display method switching unit determines the display method to be the first display method. (S21).

  In the flow 2 described above, the ratio of pixels with gradations at which flicker is easy to visually recognize is determined in stages. Therefore, unnecessary power consumption can be reduced while maintaining higher display quality. Note that flicker is less visible in the moving image than in the still image, so the conditions 3 and 4 for the moving image are stricter conditions (conditions that satisfy fewer images) than the conditions 1 and 2 for the still image, respectively. .

(Display method decision flow 3)
15A and 15B are diagrams illustrating examples of images (still images) displayed on the screen of the display device. In these images F and G, a Yes button and a No button for the user to select are arranged on a white background. For example, black characters are drawn on the white background. In the image F, the button area has a constant gradation 30, and in the image G, the button area has a constant gradation 70. In the image F, the button area of gradation 30 occupies 18% of the whole, and in the image G, the button area of gradation 70 occupies 18% of the whole. That is, in the images F and G, the areas of the gradations 0 to 5 and the gradations 200 to 255 (background area) composed of a white background and black characters occupy 80% or more of the whole.

  For these images F and G, when the display method is determined according to the above flow 1 and 2, the display is performed in the first display method (without column inversion driving or pseudo dot inversion processing). However, in the image F or the image G, the region of the gradation 30 or 70 exists in a solid state, so that when the display is performed with a low refresh rate of 10 Hz or less and the first display method, flicker may be visually recognized in the button region. is there. However, if the first threshold value for the second range (the range of gradations 20 to 80) is set to 15%, many images satisfy the condition, and even the first display method consumes power even for images where flicker is not visually recognized. Is displayed in the second display method having a large value. Therefore, in flow 3 described below, determination is performed by dividing the gradation range into small parts.

  FIG. 16 is a diagram illustrating a flowchart for determining a display method.

  The image determination unit determines whether or not the condition 5 is satisfied (S31). Condition 5 is that the ratio of pixels in the sixth range (the range of gradations 20 to 40) in the entire image is greater than or equal to the fifth threshold (15%).

  When the condition 5 is satisfied (Yes in S31), the display method switching unit determines the display method to be the second display method (with dot inversion driving or pseudo dot inversion processing) (S32).

  When the condition 5 is not satisfied (No in S31), the image determination unit determines whether or not the condition 6 is satisfied (S33). Condition 6 is that the ratio of pixels in the seventh range (the range of gradations 41 to 80) in the entire image is equal to or greater than the sixth threshold (15%).

  When the condition 5 is not satisfied and the condition 6 is satisfied (Yes in S33), the display method switching unit determines the display method to be the second display method (S34).

  When the condition 5 is not satisfied and the condition 6 is not satisfied (No in S33), the display method switching unit determines the display method to be the first display method (without column inversion driving or pseudo dot inversion processing) (S35).

  Here, the sixth range and the seventh range are continuous, but the ranges do not overlap. Further, the fifth threshold value and the sixth threshold value are the same value (15%). In this way, flicker is visually recognized in a small area such as images F and G by dividing an intermediate gradation (for example, gradation 20-80) that is likely to cause flicker into two ranges and determining the ratio of each. Images can be displayed by the second display method in which flicker is not easily seen. Therefore, the flicker can be prevented from being visually recognized even for an image such as a button area in which gradations that make it easy to visually recognize the flicker are fixed. In addition, it is possible to appropriately determine an image in which flicker is difficult to be visually recognized, and to display the image in the first display method with low power consumption.

  Note that the sixth range and the seventh range may be partially overlapped, or may be different ranges. The fifth threshold value and the sixth threshold value may be different.

[Embodiment 4]
Still another embodiment of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the block configuration of the display device is the same as that in the first or second embodiment. The image determination method described here can be applied to both the first and second embodiments.

(Image determination method 1)
In the first embodiment, the ratio of pixels having a predetermined range of gradation in the entire image is obtained. However, the ratio of pixels having a predetermined range of gradation in a partial area of the image may be obtained.

  (A) and (b) of FIG. 17 are diagrams showing screens of different display devices. The uniformity of the pixel capacitance depends on the manufacturing process. For this reason, in the screen of the display device, a region where the pixel capacity is not uniform is often biased to a certain location. For example, in the example of the display device shown in FIG. 17A, a region 12 having nonuniform pixel capacities is distributed in the center of the screen 11a. In the example of the display device shown in FIG. 17B, the region 12 where the pixel capacity is not uniform is distributed in the lower portion of the screen 11b. That is, even when an image of the same gradation is displayed on the entire screen, flicker is easily visible at the center of the screen 11a in FIG. 17A, and flicker is displayed at the bottom of the screen 11b in FIG. Is easily visible.

  Therefore, if it is determined whether or not pixels having gradations that are likely to cause flicker are distributed in the image area corresponding to the area 12 where the pixel capacity is not uniform, whether or not the image is likely to cause flicker. Can be determined.

  In the display device of FIG. 17A, the image determination units (region specifying units) 35 and 52 specify a partial region at the center of the image as the predetermined analysis region 13. In the display device of FIG. 17B, the image determination unit sets a predetermined partial area in the lower part of the image as the predetermined analysis area 13. The analysis region 13 includes a region corresponding to the region 12 where the pixel capacity is not uniform. Then, the image determination unit determines whether or not the ratio of pixels in the second range (for example, the range of gradations 20 to 80) in the analysis region 13 is equal to or greater than the first threshold (for example, 30%). To do.

  As described above, by determining the ratio of the pixels of the intermediate gradation only in a partial area of the image corresponding to the area where the flicker is likely to occur on the screen, the process of determining the gradation of the pixels can be reduced. . Also, the storage capacity for the histogram can be reduced.

  If it is determined that flicker is likely to occur in the analysis region 13 of the image (the ratio of the pixels in the second range of gradations is equal to or higher than the first threshold value), not the entire screens 11a and 11b but the screens 11a and 11b. The second display method (pseudo dot inversion processing or dot inversion driving) may be applied only to some of the regions 14, and the first display method may be applied to other regions.

(Image determination method 2)
The image determination units 35 and 52 may obtain the ratio of pixels having a gradation in a predetermined range for a plurality of regions of the image.

  In the example of the display device shown in FIG. 18A, regions 12 having nonuniform pixel capacities are distributed from the center to the bottom of the screen 11c. Therefore, the image determination unit sets a plurality of analysis regions 13a and 13b. Of the region 12 where the pixel capacity is not uniform, the central portion of the screen 11c is included in the analysis region 13a. The lower part of the screen 11c in the region 12 where the pixel capacity is not uniform is included in the analysis region 13b.

  The image determination unit determines, for each of the plurality of analysis regions 13a and 13b, whether or not the ratio of pixels in the second range of gradations (gradation that makes it easy to visually recognize flicker) is greater than or equal to the first threshold value. If it is determined that the flicker is easily visible in one of the analysis regions 13a and 13b of the image (the ratio of the pixels in the second range of gradations is equal to or higher than the first threshold), at least flicker is detected. The second display method (pseudo dot inversion processing or dot inversion driving) is applied to the analysis region determined to have a feature that is easily visible. For example, when the ratio of pixels in the second range of gradations in the analysis region 13a is greater than or equal to the first threshold, the display method switching unit performs pseudo dot inversion processing on the pixels in the second range of gradations in the analysis region 13a. Apply.

  For example, for the region 14a of the screen 11c, the display method is determined according to the gradation of the plurality of pixels in the corresponding analysis region 13a, and for the region 14b of the screen 11c, the plurality of pixel levels in the corresponding analysis region 13b. The display method is determined according to the key. The other areas of the screen 11c are always displayed by the first display method. Note that the display method switching unit may display the entire image in the second display method when it is determined that the flicker is easily visible in any analysis region.

  As shown in FIG. 18B, the image determination unit divides the entire image (screen 11d) into a plurality of analysis regions 13c to 13h, and the ratio of the pixels in the second range of gradations for each analysis region is the first. You may determine whether it is 1 threshold value or more. In this case, the image determination unit generates a histogram for classifying pixels for each analysis region. For example, for each analysis region, whether to display using the first display method or to display using the second display method may be determined according to the determination result of the image determination unit.

  In addition, the conditions for determination may differ for every some analysis area | region 13c-13h. For example, the image determination unit determines whether the analysis region 13e satisfies the condition that the pixels in the second range of gradations are equal to or greater than the first threshold, and the analysis region 13f has a third range different from the second range. It may be determined whether or not the condition that the pixel of the gray scale is equal to or higher than a second threshold different from the first threshold is satisfied.

  By performing the determination for each of the plurality of analysis regions, it is possible to appropriately change the display method even for an image in which pixels in which flicker is likely to be visually recognized are locally gathered, thereby preventing the flicker from being visually recognized. Further, for an image (or region) where flicker is difficult to be visually recognized, power consumption can be reduced by performing display using the first display method with low power consumption.

(Image determination method 3)
By determining whether there is an area that matches a predetermined pattern in the image, it is also possible to determine whether the image has an area where flicker is likely to occur.

  FIG. 19A shows a predetermined pattern 15. The pattern 15 is a rectangular pattern composed of 3 rows × 6 columns of pixels. “1” indicates that the gradation of the corresponding pixel is within the second range (range of gradations 20 to 80), and “0” indicates that the gradation of the corresponding pixel is not within the second range. That is, the pattern 15 is a pattern configured by two-dimensionally collecting a plurality of pixels having the gradation of the second range.

  FIGS. 19B and 19C are diagrams showing a gradation map representing the gradation of each pixel of the image. The image determination unit determines whether or not the gradation of each pixel of the image is in the second range, and generates gradation maps 16a and 16b. In the gradation maps 16a and 16b, the value is “1” if the gradation of the pixel is within the second range, and the value is “0” if the gradation of the pixel is not in the second range.

  As shown in the gradation map 16b in FIG. 19C, even if there are many pixels having the gradation in the second range, if the pixels having the gradation in the second range are roughly dispersed, the flickering Is difficult to see. As shown in the gradation map 16a of FIG. 19B, if a region where pixels in the second range of gradation are densely distributed exists locally, the gradation is in the second range in the whole. Even if the ratio of pixels is small, flicker is easily visible. In other words, if the pixels having the gradation in the second range are present in a certain region or more, flicker is more visible.

  The image determination unit determines whether there is a region that matches the predetermined pattern 15 in the gradation maps 16a and 16b. The display method switching unit switches the display method depending on whether or not the image has a region matching the pattern 15.

  A gradation map 16 a of an image has a region 17 that matches the pattern 15. For this reason, the image corresponding to the gradation map 16a is likely to cause flicker, and the display method switching unit determines to display the image in the second display method. The gradation map 16 b of another image does not have an area that matches the pattern 15. Therefore, the image corresponding to the gradation map 16b is less likely to cause flicker, and the display method switching unit determines to display the image in the first display method.

  In this way, by determining the display method according to whether or not the image matches the predetermined pattern 15, an image in which flicker is likely to be visually recognized locally (FIG. 19B) is displayed in the second display method ( Display with pseudo dot inversion processing or dot inversion driving) to prevent the flicker from being visually recognized. In addition, an image (FIG. 19C) that includes many pixels in the second range of gradation but is difficult to visually recognize flicker is displayed in the first display method (without pseudo dot inversion processing or column inversion driving). Power consumption can be reduced.

  Note that the display method switching unit may determine that only the partial region of the image corresponding to the matching region is displayed in the second display method. Further, even if it is not 100% perfect match, if there is an area in the image that matches the pattern 15 by a predetermined ratio (for example, 80%) or more, the display method switching unit displays the image in the second display method. You may decide.

  In the above example, pattern matching is performed regardless of the pixel color, but pattern matching may be performed for each picture element. In other words, the image determination unit generates a gradation map indicating whether the luminance Y of the picture element is within a predetermined range, and determines whether or not a predetermined pattern composed of a plurality of picture elements matches the image. May be. The image determination unit may generate a gradation map for each RGB color for one image, and determine whether a predetermined pattern matches the gradation map for each color.

(Other image determination methods)
In addition to the image determination method described above, the image determination unit may determine that the image has a feature that makes it easy to visually recognize flicker when a predetermined pattern (for example, a stripe pattern) exists in the image. . Since the saturation gradation pixel has a small potential fluctuation with time, flicker is easily recognized when an intermediate gradation pixel is adjacent to a saturation gradation (highest gradation or lowest gradation) pixel. When the image has such a predetermined pattern, display can be performed by the second display method, thereby preventing flicker from being visually recognized.

[Embodiment 5]
Still another embodiment of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the image determination unit, the display method switching unit, and the image processing unit are provided in a display drive unit that is a COG driver.

(Configuration of display device 3)
FIG. 20 is a block diagram showing the configuration of the display device of this embodiment. The display device 3 includes a display unit 10, a display drive unit 70 (control device), and a host control unit 60. The configuration of the host control unit 60 is the same as that of the second embodiment. The host controller 60 transfers the display data of the updated image to the display driver 70 only when the display needs to be updated.

  The display driving unit 70 is a COG driver that is COG-mounted on the glass substrate of the display unit 10, and drives the display unit 10. The display drive unit 70 includes an image processing unit 51, an image determination unit 52, a display method switching unit 53, a memory 21, a TG 22, and a source driver 23. The operation of each part of the display driving unit 70 is the same as that of the second embodiment.

  Note that the image determination unit 35, the display method switching unit 36 for switching the inversion driving method, and the gamma correction unit 37 of the first embodiment may be provided in the display driving unit as in the present embodiment.

  In this embodiment, the display method is determined by the COG driver (display drive unit 70). Thereby, the load on the host control unit 60 can be reduced without providing a separate substrate from the host control unit 60. Since the COG driver formed on the active matrix substrate has a limited mounting area, this embodiment is suitable when only simple processing is performed in the image processing unit 51, the image determination unit 52, and the display method switching unit 53. .

[Summary]
The display device (1, 2, 3) according to aspect 1 of the present invention includes a first pixel (PIX1) that displays a certain color in the first picture element (PE1), and a second picture adjacent to the first picture element. The display panel (10) including the second pixel (PIX2) for displaying the color in the element (PE2) and the image indicated by the display data in a certain period are images (flicker image) having a feature that makes flicker easy to see. If it is determined that the image determination unit (35, 52) determines whether or not the image in the period has characteristics that make it easy to visually recognize flicker, the image is displayed by the first display method in the period. On the other hand, when it is determined that the image in the period has a feature that makes it easy to visually recognize the flicker, a display method switching unit that switches the display method so that the image is displayed in the second display method in the period ( 6 and 53) and the first display method, when the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same, While the same potential is written to the pixel and the second pixel, in the second display method, the gradation of the display data corresponding to the first pixel is the same as the gradation of the display data corresponding to the second pixel. Even in this case, the pixel writing unit (source driver 23) for writing different potentials to the first pixel and the second pixel is provided.

  For example, the first display method is a display method that consumes less power than the second display method, and the second display method is a display method in which flicker is less visible than the first display method.

  According to the above configuration, the display method can be switched according to whether or not the image has a feature that makes it easy to visually recognize flicker. In the first display method, when the gray level of the display data corresponding to the first pixel and the gray level of the display data corresponding to the second pixel are the same, the pixel writing unit simply performs the first display. The same potential is written to one pixel and the second pixel. On the other hand, in the second display method, even when the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same, the flicker is visually recognized. In order to prevent this, the pixel writing unit writes different potentials to the first pixel and the second pixel. That is, in the second display method, when the gradations of the display data corresponding to the first pixel and the second pixel are the same, the gradation is represented by an average of the luminance of the first pixel and the second pixel. . Therefore, in the second display method, it is possible to prevent flicker from being visually recognized. Therefore, it is possible to realize a display device that suppresses power consumption and performs good display by switching display methods according to image characteristics.

  The display device according to aspect 2 of the present invention is the display apparatus according to aspect 1, in which the first pixel and the second pixel are adjacent to each other in the column direction, and the pixel writing unit is a column in the first display method. Display is performed by inversion driving, and display is performed by dot inversion driving in the second display method, and the display method switching unit switches the display method of the pixel writing unit to column inversion driving according to the determination result of the image determination unit. And dot inversion driving may be switched.

  According to the above configuration, the display device displays an image that does not have a feature that makes it easy to visually recognize flicker by column inversion driving, and displays an image that has a feature that makes it easy to visually recognize flicker by dot inversion driving. The column inversion drive consumes less power than the dot inversion drive, and the dot inversion drive makes it difficult to see flicker compared to the column inversion drive. Therefore, power consumption can be reduced by column inversion driving for images that do not have a feature that makes flicker easy to see, and good display can be made by dot inversion driving for images that have a feature that makes flicker easy to see. it can.

  In the display device according to aspect 3 of the present invention, in the aspect 2, when the gradation corresponding to the first pixel is the gradation in the first range in the intermediate gradation, the display in the first display method is the above. The potential that the pixel writing unit writes to the first pixel and the potential that the pixel writing unit writes to the first pixel in the second display method have the same polarity and different sizes. May be.

  The display device according to aspect 4 of the present invention is the gamma correction unit that performs gamma correction on the display data using different parameters in the first display method and the second display method in the aspect 2 or 3. May be provided.

  In the display device according to aspect 5 of the present invention, in the aspect 4, the gamma correction unit has the same gradation-luminance characteristic in the first display method and gradation-luminance characteristic in the second display method. As such, it may be configured to perform gamma correction.

  The display device according to aspect 6 of the present invention is the display apparatus according to aspect 1, in which the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are intermediate gradations. In the second display method, image processing is performed so that the gradation corresponding to the first pixel is converted to high and the gradation corresponding to the second pixel is converted to low. The image processing unit for performing the above may be provided.

  The second range is a gradation range that is determined in advance as a gradation that makes it easy to visually recognize flicker within the intermediate gradation range.

  According to the above configuration, in the second display method, the gradation in the second range corresponding to the first pixel and the second pixel can be expressed by the average of the gradation converted to the high and the gradation converted to the low. it can. Therefore, the flicker can be prevented from being visually recognized by the second display method with respect to an image having a feature that makes it easy to visually recognize the flicker.

  In the display device according to aspect 7 of the present invention, in the aspect 6, the image processing unit may be configured not to perform the image processing in the first display method.

  In the display device according to aspect 8 of the present invention, in the aspect 7, when the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same, The image processing unit performs the image processing so that the average luminance of the first pixel and the second pixel in the second display method is the same as the luminance of the first pixel in the first display method. It may be a configuration.

  In the display device according to aspect 9 of the present invention, in the above aspects 6 to 8, in the second display method, the image processing unit has gradations of the display data corresponding to a plurality of pixels displaying the color. A checkered pattern is formed by detecting a region having a predetermined size or more that is the same and having the gradation in the second range, and a pixel whose gradation is increased by the conversion and a pixel whose gradation is decreased by the conversion. The image processing may be performed on the region of the image so as to line up.

  In the display device according to aspect 10 of the present invention, in the aspect 9, the image processing unit includes the pixel that increases in gradation by the conversion in the second display method and the pixel that decreases in gradation by the conversion. The image processing may be performed such that the average luminance is the same as the luminance of the pixels in the region in the first display method.

  In the display device according to aspect 11 of the present invention, in any of the above aspects 6 to 10, in the second display method, the image processing unit may convert the gradation corresponding to the converted first pixel and the converted first pixel. The image processing may be performed so that the gradation corresponding to the two pixels is outside the second range.

  In the display device according to aspect 12 of the present invention, in the above-described aspects 1 to 11, the pixel writing unit is configured to change the content of the image indicated by the display data to the first pixel and the second pixel. The display may be updated at the earlier of the timing at which the predetermined period has elapsed since the potential was written, and the predetermined period may be longer than the display update interval when the moving image is displayed.

  In the display device according to aspect 13 of the present invention, in the above aspects 1 to 12, the image determination unit has a ratio of pixels that are gradations in a second range of intermediate gradations in a predetermined region of the image. It may be configured to determine whether or not the image in the period has a feature that makes it easy to visually recognize flicker depending on whether or not the first threshold value or more.

  A display method according to aspect 14 of the present invention is a display method of a display device, wherein the display device includes a first pixel that displays a certain color in the first picture element, and a second pixel adjacent to the first pixel. An image determination step of determining whether or not an image indicated by display data in a certain period is an image having a characteristic that makes flickering easily visible, including a display panel including a second pixel that displays the color in the picture element; When it is determined that the image in the period does not have a feature that makes flicker easily visible, the image is displayed in the first display method in the period, while the image in the period has a feature that makes flicker easy to see. If it is determined, the display method switching step for switching the display method so that the image is displayed in the second display method in the period, and the first image in the first display method. When the gray level of the display data corresponding to the second pixel and the gray level of the display data corresponding to the second pixel are the same, the same potential is written to the first pixel and the second pixel, while the second display In the method, even if the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same, the first pixel and the second pixel And a pixel writing step of writing different potentials.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  The present invention can be used for a display device.

1, 2, 3 Display device 10 Display unit (display panel)
20, 40, 70 Display driver (control device)
23 Source driver (pixel writing unit)
30, 60 Host control unit (control device)
31, 61 Screen update detection unit (update detection unit)
35, 52 Image determination unit (region specifying unit)
36, 53 Display system switching unit 37 Gamma correction unit 50 Display control unit (control device)
51 Image Processing Unit PIX1 First Pixel PIX2 Second Pixel PE1 First Picture Element PE2 Second Picture Element

Claims (6)

A first pixel displaying a color with the first picture element, and a display panel and a second pixel for displaying the color in a second pixel adjacent in the column direction for the said first picture element,
Depending on whether or not the ratio of pixels in the second range of intermediate gradations in the predetermined area of the image indicated by the display data in a certain period is greater than or equal to the threshold, the image in the period will flicker. An image determination unit that determines whether or not the image has a feature that is easily visible ;
When it is determined that the image in the period does not have a feature that makes flicker easily visible, the image is displayed in the first display method in the period, while the image in the period has a feature that makes flicker easy to see. If determined, a display method switching unit that switches a display method so that the image is displayed in the second display method during the period;
In the first display method, when the gray level of the display data corresponding to the first pixel and the gray level of the display data corresponding to the second pixel are the same, the first pixel and the second pixel In the second display method, the gradation of the display data corresponding to the first pixel and the gradation of the display data corresponding to the second pixel are the same. And a pixel writing section for writing different potentials to the first pixel and the second pixel,
The pixel writing unit performs display by column inversion driving in the first display method, and performs display by dot inversion driving in the second display method.
The display device, wherein the display method switching unit switches the display method of the pixel writing unit between column inversion driving and dot inversion driving in accordance with a determination result of the image determining unit . In a case where the gray level corresponding to the first pixel is a gray level in a first range of intermediate gray levels, the pixel writing unit writes the first pixel in the first display method, and the first pixel 2. The display device according to claim 1 , wherein in the two-display method, a potential written to the first pixel by the pixel writing unit has the same polarity and a different magnitude. Above the first display method and the second display method, the display device according to claim 1 or 2, characterized in that it comprises a gamma correction unit for performing gamma correction with different parameters with respect to the display data. The gamma correction unit, the gradation in the first display method - and luminance characteristics, gradation in the second display mode - as the luminance characteristics are the same, claim 3, wherein the performing gamma correction The display device described in 1. The pixel writing unit, when displaying a still image, the timing at which the content of the image indicated by the display data changes, and the timing when a predetermined period has elapsed since the potential was written to the first pixel and the second pixel. To update the display,
The display device according to any one of claims 1 to 4 , wherein the predetermined period is longer than a display update interval when displaying a moving image. A display method for a display device, comprising:
The display device, the display comprising a first pixel displaying a color with the first picture element, and a second pixel for displaying the color in a second pixel adjacent in the column direction for the said first picture element With panels,
Depending on whether or not the ratio of pixels in the second range of intermediate gradations in the predetermined area of the image indicated by the display data in a certain period is greater than or equal to the threshold, the image in the period will flicker. An image determination step for determining whether or not the image has a feature that is easily visible ;
When it is determined that the image in the period does not have a feature that makes flicker easily visible, the image is displayed in the first display method in the period, while the image in the period has a feature that makes flicker easy to see. If determined, a display method for switching the display method between column inversion driving and dot inversion driving according to the determination result in the image determining step so that the image is displayed in the second display method during the period. A switching step;
In the first display method, when the gray level of the display data corresponding to the first pixel and the gray level of the display data corresponding to the second pixel are the same, the first pixel and the second pixel as it writes the same potential, while the images are displayed by column inversion driving, in the second display mode, the floor of the display data corresponding to the gradation and the second pixel of the display data corresponding to the first pixel A pixel writing step of performing display by dot inversion driving so that different potentials are written to the first pixel and the second pixel even when the tone is the same. .

Images