JP3346911B2 - Driving method of display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a display device in which switch elements for selection are provided for each pixel or each scanning line, and more particularly to a method for driving a liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device is thin and lightweight and can be driven at a low voltage.
And it is widely used for small game machines and the like. Furthermore, the need for a pen-input electronic notebook has been increasing, and the demand for a portable terminal (PDA) has been expanding.

On the other hand, with the progress of multimedia, a plurality of displays will be displayed on the same screen. If a large screen and high definition are required, the amount of information will increase and the driving frequency will increase. The increase in power consumption due to this causes a problem, and a driving method for lowering power consumption (for example, Japanese Patent Application No. 2-69706).
Has been proposed. This method is herein referred to as a multi-field driving method. This multi-field driving method
This is a very effective means for surface flicker, but since the holding period is greatly increased, the flicker component for each pixel (usually for each line) increases. For this reason, there is a problem that horizontal stripes (line disturbance) generated for each field are visually recognized and image quality of a still image is deteriorated.

Further, in a high-definition image in which there is no correlation between images, each flicker component is not compensated, and a new carrier generated by the difference between the positive polarity and the negative polarity in the flicker component is generated on the spatial frequency axis. It has been clarified from experiments that it occurs on the upper surface, which causes aliasing. Since this aliasing distortion is not stationary but moving, if it enters a region visually recognized by the spatio-temporal frequency characteristics, the image quality is greatly deteriorated.

As described above, in the multi-field driving method, the line disturbance and the aliasing caused by the line disturbance degrade the image quality. Usually, as a means for correcting this, correction is performed during a blanking period (retrace period), but this has been insufficient.

[0006] As for moving images, another problem is that the drive frequency is lowered, so that the signals cannot be sufficiently rewritten and an afterimage phenomenon occurs. Therefore, for a moving image, means for a signal processing system is required separately.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention relates to a visual spatio-temporal analysis of a carrier distortion caused by a difference between a positive polarity and a negative polarity among flicker components which cannot be sufficiently compensated by each flicker component. An object is to make the region invisible in frequency characteristics.

Another object of the present invention is to perform random driving in accordance with a signal in order to suppress the occurrence of an afterimage phenomenon for a moving image having a higher frequency than the driving frequency such as a moving image.

[0009]

In the driving method according to the present invention, each of the driving methods is provided with a switching element for selection.
In a display device that displays an image using pixels or scanning lines, one frame image is divided into n subfields that are sequentially displayed along a time axis, and the subfield is divided into a plurality of pixels or scanning lines. A ÷ n × m within
(Where A is a positive integer, n is a positive integer of 3 or more and A or less, and m is a positive integer of n or less) pixels or scanning lines.

In order to improve the image quality, it is desirable that flicker can be compensated between a pixel or a scanning line to be written and a neighboring pixel or scanning line.

When an image is displayed by a scanning line, an image signal of one frame image is interlaced by n: m, and the switch element can be selectively driven according to the processed image signal.

A first aspect of the present invention is characterized in that intervals between the pixels or the scanning lines are different for each subfield, and the intervals are irregularly changed along a time axis.

A second aspect of the present invention is characterized in that the value of m / n is changed depending on the image signal.

According to a third aspect of the present invention, the subfields are grouped along a time axis, and the value of m / n is different for each group.

In order to compensate for a change in screen brightness due to switching of the value of m / n, a function is provided to detect the screen brightness of the previous subfield at the time of switching and to provide feedback to the screen brightness of the next subfield. Can be

A fourth aspect of the present invention is characterized in that writing is selectively performed on displacement pixels or scanning lines among pixels or scanning lines that do not belong to a displayed subfield or scanning line. I do.

In the case where writing is not performed in a certain pixel or a scanning line over several frames, a function of performing writing again may be provided in order to compensate for uneven brightness in a screen.

In the second to fourth aspects of the present invention,
Preferably, the intervals between pixels or scanning lines are different for each subfield.

[0019]

According to a first aspect of the present invention, the switching elements are periodically and spatially and temporally turned on and off so that the interval between pixels or scanning lines changes irregularly for each subfield. I can't. Thereby, for example, since the luminance change of the pixel due to the holding characteristic of the liquid crystal does not have a spatial and temporal periodicity in the panel surface, it does not apply to the region visually recognized from the visual characteristic or becomes difficult to be visually recognized. .

For example, when an image signal is interlaced by n: m in order to display an image on a scanning line, the interval between the selected scanning lines changes irregularly during one frame. Therefore,
Since the scanning lines that are turned on during the field period have no spatial periodicity in the panel surface, for example, a change in pixel luminance (line disturbance) due to the liquid crystal holding characteristics is recognized in an area where the visual characteristics show. It does not apply or becomes difficult to be visually recognized, and the deterioration of image quality can be greatly improved.

Further, in a high-definition image in which there is no correlation between images, when a new carrier generated by the difference between the positive and negative flicker components is generated on the spatial frequency axis, thereby causing aliasing distortion, Since this aliasing distortion does not have spatial periodicity, the aliasing distortion does not apply to the visual spatio-temporal frequency characteristics, or it is hard to be visually recognized, and the deterioration of image quality can be greatly improved.

According to the second aspect of the present invention, for example, the value of m / n can be appropriately changed between a moving image and a still image. According to a third aspect of the invention, a certain m / n
Even if an image signal which is likely to generate flickers is input by driving at a value of?, Since the image signal is switched for each subfield group, the flicker generation pattern differs for each group, making it difficult to visually recognize the image signal.

In the second and third viewpoints, when the screen luminance of the previous subfield at the time of switching is detected and feedback is applied to the screen luminance of the next subfield, the screen is changed by changing the value of m / n. Brightness changes can be compensated.

According to the fourth aspect of the present invention, it is possible to eliminate an afterimage caused by, for example, a luminance difference. For a moving image having a higher information frequency than the driving frequency, such as a moving image, one frame of the image signal is subsampled and displayed, so that one frame of the image signal is divided into a plurality of subfields. For this reason, for the pixel once written, the image at the time of writing is held during the non-selection period until writing again, and a signal extremely different from the luminance at the time of writing is input during the non-selection period. Is not written even if it is written as an image. Therefore, a signal having a different luminance level between the previous frame and the next frame is selectively driven to prevent an afterimage.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (First Embodiment) In the first embodiment, a multi-field driving method is applied in which one frame (one frame image) is divided into a plurality of sub-fields (sub-images) to lower the driving frequency. . Since the multi-field driving method is well known, a detailed description thereof will be omitted.

FIG. 1 shows a configuration of a main part of a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal display device of this embodiment is
As shown in FIG. 1A, a liquid crystal display panel 12, a subfield division processing unit 14, a signal line driver 16,
A pixel or scanning line selection signal generation circuit 18 and a gate line drive circuit 22 are provided. Liquid crystal display panel cell 24
Has a configuration (for example, a segment type display) that can be selected for each pixel, as shown in FIG.
Even if the interval between pixels constituting each subfield is irregular, that is, if the interval between selected pixels changes for each subfield, it is possible to cope with it.

The contents of the processing performed by the subfield division processing unit 14 may be any contents, but in the present embodiment, the processing for improving the deterioration of the display image which is a problem in the prior art is improved. Processing content.

In order to facilitate understanding, as shown in FIG. 2, a driving method according to the present embodiment will be described with an example in which three pixels out of nine pixels are selected (the number of subfields is 9/3 = 3). Will be described.

First, in the subfield division processing section 14, for example, as shown in FIG. 2, the pixel 26 is selected, and three subfields SF11 to SF13 are formed. FIG.
The middle and shaded portions are selected pixels, and the white portions are non-selected pixels. In this case, since the image signal to be read by the subfield division processing unit 14 is reduced to one third of the conventional one, the driving frequency can be reduced as is well known in the multi-field driving method. In addition, the power consumption of the signal line driver 16 can be reduced.

When an image signal is written to each pixel in the panel 12, a signal indicating which pixel should be selected from the pixel selection signal generation circuit 18 is sent to the gate line drive circuit 2
2 and is controlled so that the gate line corresponding to each pixel is turned on.

The purpose of the sub-field division processing unit 14 is to prevent line disturbance, which is a cause of aliasing, from occurring fundamentally, and to set the interval between selected pixels in an area where visual spatio-temporal frequency is not visible. This is most effective.

In this embodiment, a case has been described in which the same number of pixels are selected in each subfield so that the pixel interval changes irregularly along the time axis. However, the number of selected pixels and the selection method are various. Can be changed in the following manner. Further, the present embodiment can be applied to a case where substantially the same number of scanning lines are selected in each subfield so that the scanning line intervals change irregularly along the time axis. (Second Embodiment) The second embodiment is a modification of the first embodiment, and is also performed by dividing one frame (one frame image) into a plurality of sub-fields (sub-images). This is an application of a multi-field driving method for lowering the frequency. Since the multi-field driving method is well known, a detailed description thereof will be omitted.

FIG. 3 shows a configuration of a main part of a liquid crystal display device according to a second embodiment of the present invention. The liquid crystal display device of this embodiment is
As shown in FIG. 3A, in particular, an n: m interlace processing circuit 34 and a scanning line selection signal generation circuit 38 are provided. In addition, the liquid crystal display device of this embodiment includes a liquid crystal display panel 32, a signal line driver 36, an n counter circuit 40, and a gate line driving circuit 42. The configuration of the gate line driving circuit 42 is as shown in FIG.

The content of the processing performed by the interlace processing circuit 34 may be any content, but in this embodiment, the content of the processing for improving the deterioration of the display image which is a problem in the prior art is described. It has become.

For easy understanding, as shown in FIG. 4, n = 6 and m = 2 (the number of subfields is 6 ÷ 2 = 3).
The driving method according to the present embodiment will be described by taking a case as an example.

First, the n: m interlace processing circuit 34
In FIG. 4, for example, a pixel corresponding to the scanning line 46 is selected as shown in FIG.
23. In FIG. 4, the hatched portion is a selected scanning line, and the white portion is a non-selected scanning line. In this case, since the image signal to be read by the interlace processing circuit 34 is reduced to one third of the conventional one, the driving frequency can be reduced as well known in the multi-field driving method, and the driving circuit 42 and the panel 32 Power consumption can be reduced.

When an image signal is written to each pixel in the panel 32, a signal (S1) indicating which pixel should be selected from the scanning line selection signal generation circuit 38 is sent to the gate line drive circuit 42. , And a signal obtained by shifting the signal (S2) from the n-counter circuit 40. As a result, control is performed so that the gate line corresponding to each pixel is turned on.

FIG. 5 shows a signal waveform corresponding to each signal line. In the figure, "input", "S3", "Gn", "Pn"
Indicates an input image signal, a signal from the signal line driver 36 to the panel 32, ON / OFF of each gate line, and a voltage of a pixel corresponding to each scanning line, respectively.

Even if the n: m interlacing process is performed, line disturbance, which is a cause of aliasing, occurs. However, as shown in FIG. 6, the space between line disturbances and the horizontal stripe flow that occurs when scanning lines are sequentially scanned from the upper line to the lower line are eliminated, so that the spatio-temporal spectrum of the line disturbance is dispersed and becomes less visible. At the same time, it has been confirmed from experiments that it is effective for aliasing. FIG. 6 shows a change in luminance of a pixel corresponding to a scanning line when the method according to the present embodiment is used (a) and when the conventional multi-field driving method is used (b). In the figure, the luminance changes from light to dark and the pixel voltage changes from low to high in the order of white, diagonal, and halftone lines.

In the above description, the case where the input signal is interlaced to 6: 2 is exemplified. However, the gist of the present invention is not limited to a normal n: 1 interlace signal or an n: m (m <n) interlace signal. It can be changed without departing from the scope.

In the first and second embodiments, as a method of selecting a pixel for forming a subfield, it is preferable that flicker is compensated in one frame in order to improve image quality. Since the line disturbance is caused by the retention characteristics of the pixels, the selection interval of the pixels or the scanning lines is a 10% level image signal in which crosstalk easily occurs or a 50% level image signal in which the transmittance changes sharply. It is desirable to determine such that no line disturbance or aliasing distortion occurs. (Third Embodiment) In the present invention, an image is displayed by changing the interval between the pixels or the scanning lines in accordance with the input image signal, so that processing in the image signal input section is required. Since an image signal of one frame is divided into a plurality of subfields, once written pixels retain the written image during the non-selection period until they are written again. Therefore, a signal requiring a sample frequency in the time axis direction such as a moving image is not written even if a signal extremely different from the luminance at the time of writing is input during the non-selection period. come.

FIG. 7 shows an afterimage phenomenon when a cursor such as a mouse is moved in the case of 3: 1, 5: 2, 3: 2 interlace driving. In the case of 3: 1 interlace driving, there are many afterimages and almost no new image signal appears. In the 5: 2 interlace driving, there is an afterimage, but a new image signal also appears. In 3: 2 interlace driving, afterimages are few and many new images appear. The change in the image signal due to the increase in the number of subfields in one frame is remarkable.

FIG. 8 shows a structure of a main part of a liquid crystal display device according to a third embodiment of the present invention. The liquid crystal display device of this embodiment is
As a change from the second embodiment shown in FIG. 3, a moving image / still image detection processing unit 52 and n: m = 3:
3, 5: 2, 3: 2 interlace processing circuit 5
4a, 54b, 54c, a multi-field driving method selection processing section 56, and interlace processing circuits 54a, 54
b, 54c. The moving image / still image detection processing section 52 determines an appropriate multi-field driving method for the next frame, and
Switch. In each of the n: m interlaced driving, the scanning lines may be changed at irregular intervals as described in the second embodiment. (Fourth Embodiment) FIG. 9 shows a configuration of a main part of a liquid crystal display device according to a fourth embodiment of the present invention. The apparatus according to the present embodiment is premised on having a basic configuration for performing multi-field driving. However, the configuration for multi-field driving is, for example, the same as that described in the first embodiment, Here, it is omitted.

The liquid crystal display device of the present embodiment has a liquid crystal display panel 62, a signal line driver 66, a pixel selection signal generation circuit 68, a gate line drive circuit 72, a displacement pixel detection circuit 64 and a pixel signal generation circuit. 74 is provided. The cells of the liquid crystal display panel are configured to be selectable for each pixel (for example, a segment type display).

The displacement pixel detection circuit 62 detects a displacement pixel of a signal different between the previous frame and the next frame. In response, the pixel signal generation circuit 74 outputs the changed image signal, and the pixel selection signal generation circuit 68
Selects a pixel. That is, writing is performed by selecting only the displacement pixels. For this reason, the signal of the previous frame is temporarily recorded in the frame memory, and the selection or non-selection of the signal is determined based on the correlation with the next frame.

Since the afterimage is caused by the luminance difference between the previous frame and the next frame, for example, only the high-order bit of the gradation signal
Alternatively, a pixel obtained by summing them may be subsampled and used as a selection criterion. As a result, the signal processing system can be implemented with a simpler configuration. For example, for an image signal composed of a 4-bit grayscale signal, the high-order 2 bits are used as a selection criterion, and when H is input in the previous frame and L is input in the next frame, The image signal is selected.

In addition, in consideration of the retention characteristics of the pixels, a function of rewriting may be provided for pixels for which writing is not performed for several frames in order to compensate for uneven brightness in the screen.

In the above description of the present embodiment, description has been made assuming that a mutated pixel is detected. For example, the present invention is applied to a configuration in which a cell of a liquid crystal display panel can be selected for each pixel as in the first embodiment. be able to. If a displacement scan line is detected instead of a mutated pixel, n:
It can be applied to m-interlace driving. As described above, the fourth embodiment can be applied to all of the multi-field driving methods (including the conventional method) in which selected and unselected pixels (scanning lines) are generated. (Fifth Embodiment) The liquid crystal display device of the fifth embodiment is different from the liquid crystal display device of FIG. 1 described in the first embodiment in that n: m is changed for each group including a plurality of subfields. Features.

For example, as shown in FIG. 10, in a first group G1 consisting of X subfields, one out of every three
(3: 1) scanning lines, and in the second group G2 composed of the next Y subfields, two out of five (5: 2) scanning lines are driven, and the next Z scanning lines are driven. In the third group G3 composed of subfields, one out of five (5: 1) scanning lines is driven. Here, X, Y, and Z are multiples of 3, 5, and 5 corresponding to n of n: m, respectively.

The number of subfields in one group may be different or the same. In each of the n: m interlaced driving, as described in the second embodiment, the scanning lines may have irregular intervals.
Alternatively, it may be changed regularly like a conventional multi-field driving method. Further, although an example for each scanning line is shown here, it may be performed for each pixel.

According to the present embodiment, when an image signal which is liable to generate flicker is input when driving at a certain pixel or scanning line interval, this interval is switched for each subfield group. The flicker occurrence pattern differs for each group, making it difficult to visually recognize the flicker. Switching this interval may cause surface flicker due to a change in screen luminance. However, this surface flicker may cause a problem by lowering the visual frequency and time to below the invisible time frequency and contrast. Can be prevented.

In order to compensate for this surface flicker, the average brightness of the screen in the previous subfield at the time of switching is detected, and the brightness of the screen during the next subfield is fed back. It is also possible to prevent it from occurring. FIG. 11 shows a configuration of a main part of a liquid crystal display device for realizing this.

The liquid crystal display of this embodiment includes a liquid crystal display panel 82, a signal line driver 86, a scanning line selection signal generating circuit 88, and a gate line driving circuit 92. A subfield group division processing unit 94 for grouping subfields is connected to a signal line driver 86 via an image signal generation circuit 84. Further, a screen luminance detection circuit 96 is connected to the panel 82 to compensate for surface flicker. The screen luminance detection circuit 96 detects the voltage applied to the pixels of the previous subfield during the blanking period, and feeds the information to the image signal of the next field through the surface flicker prevention processing unit 98.

In the above description of the fifth embodiment, the subfields are grouped irrespective of the frame image unit. However, the grouping of the subfields may be combined with the unit of the frame image, and each group may be composed of one frame or plural frames. The number of frames in each group may be the same or different. In this way, when an image signal that is likely to cause flicker is input when driven at a certain pixel or scanning line interval, the interval is switched for each frame group, so that the flicker occurrence pattern is visually recognized. It is hard to be done.

As described above, the present invention has been described with reference to the illustrated embodiments. However, the present invention is not limited to each embodiment, and various modifications can be made without departing from the scope of the invention. is there.

[0056]

According to the present invention, the interval between pixels or scanning lines is made different for each subfield, and this is changed irregularly along the time axis, whereby the luminance change of the pixels or scanning lines can be visually recognized. It becomes difficult. Further, the aliasing distortion is hardly visually recognized, and the deterioration of the image quality can be greatly improved.

Further, according to the present invention, the value of m / n, that is, the density of pixels or scanning lines in a subfield is changed depending on the image signal, so that even if the driving frequency is lowered, it is possible to respond to the image. Required image quality can be maintained.

According to the present invention, by changing the value of m / n for each group divided along the time axis, the flicker occurrence pattern differs for each group, making it difficult to visually recognize the flicker.

Further, according to the present invention, by selectively additionally writing a displacement pixel or a scanning line, for example, an afterimage caused by a luminance difference can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing subfields according to a driving method according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing subfields according to a driving method according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a drive signal voltage and a timing chart in a drive method according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a comparison between a driving method according to a second embodiment of the present invention and a conventional multi-field driving method with respect to a horizontal stripe flow phenomenon.

FIG. 7 is a diagram showing a display image when an image signal is switched in a moving image.

FIG. 8 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing subfields according to a driving method according to a fifth embodiment of the present invention.

FIG. 11 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a fifth embodiment of the present invention.

[Explanation of symbols]

12, 32, 62, 82: liquid crystal display panel, 14: subfield division processing section, 16, 36, 66, 86 ... signal line driver, 18, 38, 68, 88 ... pixel or scanning line selection signal generation circuit, 22 , 42, 72, 92... Gate line drive circuits, 34, 54a, 54b, 54c... N: m interlace processing circuits, 40.
.. A moving image / still image detection circuit, 56 a multi-field driving method selection processing unit, 58 a switch, 64 a displacement pixel detection circuit, 74, 84 a pixel signal generation circuit, 94 a subfield group division processing unit, 96 a screen Luminance detection circuit, 9
8. Surface flicker prevention processing unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 550 G09G 3/36

Claims (4)

(57) [Claims] 1. A display device for displaying an image by A pixels or scanning lines each provided with a switch element for selection, wherein n frame images are sequentially displayed along a time axis. The subfield is divided into subfields, and the subfield is A ÷ n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less;
m is basically composed of the following positive integer) number of pixels or scanning lines n, further, by Rukoto with different spacing of the pixels or scanning lines selected in each of the sub-fields, the time interval A driving method characterized by irregularly changing along an axis. 2. A display device for displaying an image by A pixels or scanning lines each provided with a switch element for selection, wherein n frame images are sequentially displayed along a time axis. The subfield is divided into subfields, and the subfield is A ÷ n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less;
A driving method, which basically comprises (m is a positive integer equal to or less than n) pixels or scanning lines, and further changes the value of n and the value of m / n depending on an image signal. 3. A display device for displaying an image by A pixels or scanning lines each provided with a selection switch element, wherein n frame images are sequentially displayed along a time axis. The subfield is divided into subfields, and the subfield is A ÷ n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less;
m is a positive integer equal to or less than n) pixels or scan lines, and the subfields are grouped along the time axis, and the value of m / n is different for each group. A driving method characterized in that: The interval wherein selected the pixels or scanning lines in each of the subfields differ That raise the Rukoto, claim 2 or 3, wherein the changing irregularly along the interval the time axis The driving method described in the above.