JP6628575B2 - Display device and brightness unevenness control method - Google Patents

Description

  The present invention relates to a display device and a luminance unevenness control method, and more particularly to a technique for suppressing the occurrence of luminance unevenness in which luminance is partially nonuniform in image data.

  In general, in a display device such as a liquid crystal display or a plasma display, “luminance unevenness” in which the luminance of image data partially becomes nonuniform may occur due to various factors. For example, luminance unevenness occurs due to pressure locally applied to the liquid crystal panel. In particular, in the case of an IPS (In Plane Switching) type liquid crystal display, it is known that luminance unevenness is significantly generated due to a slight local pressure. In addition, in the case of an in-vehicle display, there is an in-vehicle-specific environment such as contraction and expansion of a liquid crystal or a housing due to room temperature, vibration, local pressure applied to a liquid crystal panel through a touch operation on a touch panel, and luminance unevenness is likely to occur. Environment.

  Conventionally, in order to suppress such luminance unevenness, a method has been adopted in which a display state of an image is photographed by a camera for each product on a manufacturing line, and the luminance value of another pixel is corrected so as to match a bright pixel. . However, in this method, there is a problem that adjustment is necessary for each product, and the tact time becomes long. In addition, there is also a problem that the unevenness in luminance cannot be suppressed by the luminance correction performed before shipment from the factory, because the temporal change occurs in how the pressure is applied to the liquid crystal panel.

  In addition, in addition to the above, there have been proposed techniques capable of suppressing the occurrence of uneven brightness (for example, see Patent Documents 1 to 3). In the liquid crystal display device described in Patent Literature 1, a specific portion of an input video signal is identified as a black image, and the portion of the video signal identified as black is stored in a storage unit in advance of correction information. Is corrected based on The correction information stored in the storage unit is information created in advance at the time of manufacturing inspection of the liquid crystal display device.

  In the liquid crystal display device described in Patent Document 2, black unevenness information of full screen black display displayed on the display unit is stored in the storage unit. Further, based on the black unevenness information stored in the storage unit, correction information for increasing the transmittance at a position where the brightness of the image to be displayed is determined to be low is generated, and the transmittance of the display unit is determined based on the correction information. And a correction to reduce the light emission amount of the light source unit based on the correction information.

  In the liquid crystal display device described in Patent Document 3, when the image data represents the lowest luminance corresponding to black on the entire display screen of the liquid crystal panel, the driving voltage of the liquid crystal panel based on the image data is changed to the entire display screen of the liquid crystal panel. Is corrected so that the brightness increases uniformly by a predetermined amount. With this configuration, the black display is performed in a state where the brightness of the entire display screen is higher than the brightness at the lowest luminance. Therefore, it is possible to suppress luminance unevenness that is particularly conspicuous when the black display is performed on the entire display screen. it can.

  When a video signal of the same level is continuously input to the video signal input terminal, in order to solve a problem that a pseudo pattern which is a regular repetitive pattern is displayed, the noise generation circuit generates the pseudo pattern. 2. Description of the Related Art There is known a technique in which noise composed of a pseudo random pulse signal is added to a video signal to suppress generation of a pseudo pattern (for example, see Patent Document 4). Japanese Patent Application Laid-Open No. H11-163,086 discloses that a noise signal is multiplied by a coefficient corresponding to the level of an input video signal to suppress a phenomenon in which noise is conspicuous when the level of the input video signal is low. ing.

JP 2011-203588 A WO2011 / 121630 JP 2012-226198 A JP-A-8-146906

  However, in the liquid crystal display device described in Patent Literature 1, since correction is performed based on correction information created in advance during manufacturing inspection, adjustment is required for each product, and the tact time becomes longer. This causes a problem that the luminance unevenness cannot be suppressed due to a change with time after shipment from the factory.

  On the other hand, in the liquid crystal display device described in Patent Literature 2, correction information is generated based on black unevenness information detected when full screen black display is performed on the display unit. Problems do not arise. However, since the correction is performed such that the transmittance of the display unit is increased and the light emission amount of the light source unit is reduced locally at a position where the brightness of the image to be displayed is determined to be low, the brightness is analyzed. There is a problem that it is necessary to specify a correction position and to perform complicated control on hardware.

  On the other hand, in the liquid crystal display device described in Patent Document 3, since the correction is performed so that the luminance increases uniformly by a predetermined amount over the entire display screen of the liquid crystal panel, identification of a correction position and complicated control of hardware are not performed. Not necessary. However, in the case of Patent Literature 3, since the correction can be applied only when the image data represents the minimum luminance corresponding to black on the entire display screen of the liquid crystal panel, there is a problem that an image in which luminance unevenness can be suppressed is limited. there were.

  Note that the technique described in Patent Document 4 is for suppressing the occurrence of a pseudo pattern, and is not for suppressing the occurrence of luminance unevenness.

  The present invention has been made in order to solve the above-described problem, and does not depend on the change over time of the state of the display device, and does not perform complicated control regardless of the content of the displayed image. It is another object of the present invention to suppress luminance unevenness that differs for each display device.

To solve the problems described above, in the present invention, for each pixel of the image data of n bits input, the uppermost lower Kuraibi Tsu DOO data of the image data, the random number data consisting of 1 bit Dither processing is performed by performing a logical operation. In addition, it is also possible to set a threshold and generate a random number, compare whether the generated random number is larger than the set threshold, generate random number data according to the comparison result, and variably control the set threshold. Thus, the diffusion level indicating the degree to which the value of the image data is changed by the logical operation using the random number data is variably controlled.

  According to the present invention configured as described above, the brightness difference from the surrounding area occurs only in the specific area of the input image data, but the brightness difference from the surrounding pixels occurs throughout the image data. Since it is in a random state, luminance unevenness in a specific area is less noticeable. According to the present invention, since the image data is not corrected by the correction data obtained in advance, the display device does not depend on the temporal change of the state of the display device, nor does it depend on the content of the displayed image. It is possible to suppress luminance unevenness that differs for each unit. Further, since the dither processing using the random number data may be performed on the entire area of the image data, it is not necessary to specify the correction position by analyzing the luminance and perform complicated control on the hardware.

FIG. 3 is a functional block diagram illustrating a configuration example of a main part of the display device according to the present embodiment. FIG. 3 is a diagram illustrating a specific configuration example of a random number data generation unit and an error diffusion unit according to the embodiment. It is a figure showing an example of operation by a display of this embodiment. FIG. 14 is a diagram illustrating a configuration example of a display device according to a modified example of the embodiment. FIG. 14 is a diagram illustrating a configuration example of a display device according to a modified example of the embodiment. FIG. 14 is a diagram illustrating a configuration example of a display device according to a modified example of the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram illustrating an example of a main configuration of the display device according to the present embodiment. The display device of the present embodiment is, for example, a liquid crystal display device. As shown in FIG. 1, the display device of the present embodiment includes an image data input unit 10, a random number data generation unit 20, and an error diffusion unit 30 as its functional configuration.

  The image data input unit 10 inputs image data to be displayed on a display device from an image generation device (not shown). In the present embodiment, it is assumed that RGB data including R (red), G (green), and B (blue) data is input for each pixel. The input image data is a digital signal in which each of R, G, and B includes n bits (n is an arbitrary value of 2 or more).

  The random number data generation unit 20 generates random number data whose value changes for each pixel of the image data. The random number data generated by the random number data generator 20 is a digital signal composed of one bit.

  The error diffusion unit 30 performs a dither process by performing an operation using the random number data generated by the random number data generation unit 20 for each pixel of the image data input by the image data input unit 10. Specifically, the error diffusion unit 30 logically combines the data of the least significant bit (LSB) of the image data and the random number data of 1 bit for each pixel of the image data (R, G, and B data). The dither processing is performed by the calculation. The logical operation may be any of exclusive OR, OR, and AND.

  FIG. 2 is a diagram illustrating a specific configuration example of the random number data generation unit 20 and the error diffusion unit 30 according to the present embodiment. As shown in FIG. 2, the random number data generation unit 20 includes a random number generation unit 21, a threshold setting unit 22, and a comparison unit 23. The error diffusion unit 30 includes an XOR operation unit 34. The XOR operation unit 34 includes three XOR operation units 34G, 34G, and 34B corresponding to the respective data of RGB.

  The random number generator 21 generates a random number whose value changes for each pixel of the image data. The random number generated by the random number generation unit 21 is data indicating a random value represented by a digital signal of m bits (m is an arbitrary value of 2 or more).

  The threshold setting unit 22 sets a predetermined threshold consisting of m bits or less. Here, the threshold value setting unit 22 sets a threshold value smaller than the maximum value of the random numbers generated by the random number generation unit 21. In the present embodiment, the threshold setting unit 22 sets a predetermined fixed threshold.

  The comparing unit 23 compares whether the random number generated by the random number generating unit 21 is larger than the threshold value set by the threshold value setting unit 22, and generates 1-bit random number data according to the comparison result. That is, the comparison unit 23 generates a value “1” as the random number data when the random number generated by the random number generation unit 21 is larger than the threshold set by the threshold setting unit 22, and generates a value “0” otherwise.

  The XOR operation units 3G, 34G, and 34B are configured to output the least significant bit data and the 1-bit random number data output from the comparison unit 23 for each of the R data, G data, and B data input from the image data input unit 10. And exclusive OR operation.

In general, the operation of replacing RGB data with luminance data is expressed as follows.
Y = 0.229R + 0.587G + 0.114B
As described above, by operating the least significant bit data for each of the R, G, and B data by a logical operation, it is possible to change the luminance by about 4% at the maximum for each pixel.

  FIG. 3 is a diagram illustrating an operation example of the display device of the present embodiment. FIG. 3A shows image data input by the image data input unit 10. In this image data, luminance unevenness occurs in a part of the region 301. In other words, this is a state where a luminance difference from the surrounding area occurs only in the specific area 301 of the input image data.

  On the other hand, FIG. 3B shows a state after performing dither processing with random number data for each pixel on the input image. As shown in FIG. 3B, by performing the dither processing for each pixel, both the region 301 where the luminance unevenness has occurred and the other region 302 have a random luminance value for each pixel. Become like That is, in the whole area of the image data, a random state occurs in which the luminance difference from the surrounding pixels is generated in some places. As a result, the non-uniformity in luminance of the specific region 301 is less noticeable. Although the error from the surrounding pixels is diffused to the whole area of the image data, the error is about 4% at the maximum, so that it has almost no effect on the appearance.

  As described above, in the present embodiment, the dither processing using the random number data may be performed for the entire area of the image data. Therefore, in order to suppress the luminance unevenness, the correction position based on the luminance analysis (when the luminance unevenness is generated). It is not necessary to specify an area 301) and to perform complicated control on hardware such as a display panel and a backlight. Further, in the present embodiment, the image data is not corrected by the correction data obtained before shipment from the factory, so that the state of the display device does not change over time, and the image data does not depend on the content of the displayed image. In addition, it is possible to suppress luminance unevenness that differs for each display device.

  In the above embodiment, the example in which the threshold setting unit 22 sets a fixed threshold has been described, but the present invention is not limited to this. For example, by variably controlling the threshold value set by the threshold value setting unit 22, the diffusion level indicating the degree to which the value of the image data is changed by the operation using the random number data may be variably controlled. For example, it is possible to variably control the diffusion level according to the degree of black unevenness.

  FIG. 4 is a diagram illustrating a configuration example of a display device in a case where the diffusion level is variably controlled according to the degree of black unevenness. In the configuration example shown in FIG. 4, the display device further includes a black unevenness degree detection unit 41. Further, the random number data generation section 20 includes a threshold value setting section 22A instead of the threshold value setting section 22.

  The black unevenness degree detection unit 41 detects the maximum luminance difference when all the pixels of the image data input by the image data input unit 10 are black data as the black unevenness degree. For example, as shown in FIG. 3A, when image data in which all pixels are black is input by the image data input unit 10, the black unevenness degree detection unit 41 checks the brightness of all pixels in the image data, The difference between the maximum luminance and the minimum luminance is detected as the degree of black unevenness.

  Here, the pixel having the maximum luminance among all the pixels is in the area 301 where the luminance unevenness occurs. On the other hand, the pixel having the minimum luminance among all the pixels is in the area 302 where the luminance unevenness does not occur. As a result, the black unevenness degree detection unit 41 detects the difference between the maximum brightness in the area 301 where the uneven brightness occurs and the minimum brightness in the other areas 302 as the black unevenness degree.

  The threshold value setting unit 22A variably controls the diffusion level by variably controlling the threshold value set by the threshold value setting unit 22 according to the black unevenness degree detected by the black unevenness degree detection unit 41. Specifically, when the XOR operation unit 34 is used as a logical operation, as the degree of black unevenness increases, the threshold value is reduced to increase the diffusion level (the luminance value tends to change). In addition, also in the case of calculating the logical sum as the logical operation, the variable control is performed so that the larger the degree of black unevenness, the smaller the threshold value becomes. On the other hand, when calculating a logical product as a logical operation, the variable control is performed so that the threshold value increases as the degree of black unevenness increases.

  In the configuration example of FIG. 4, for example, once the threshold is set, the threshold setting unit 22A uses the value in a fixed manner. Alternatively, the set threshold value may be fixedly used for a predetermined period, and then, when the black unevenness degree detection unit 41 detects the black unevenness degree again, the threshold value may be reset. Alternatively, the threshold value may be reset every time the black unevenness degree detection unit 41 detects the black unevenness degree.

  As another example, the diffusion level may be variably controlled according to the maximum luminance of all pixels of the image data. FIG. 5 is a diagram illustrating a configuration example of a display device when the diffusion level is variably controlled according to the maximum luminance of all pixels of the image data. In the configuration example illustrated in FIG. 5, the display device further includes a maximum luminance detection unit 51. Further, the random number data generation section 20 includes a threshold value setting section 22B instead of the threshold value setting section 22.

  The maximum luminance detecting unit 51 detects the maximum luminance of all pixels of the image data input by the image data input unit 20. The threshold setting unit 22B variably controls the diffusion level by variably controlling the threshold set by the threshold setting unit 22 in accordance with the maximum luminance detected by the maximum luminance detection unit 51.

  Specifically, when the XOR operation unit 34 is used as the logical operation, the threshold value setting unit 22B increases the threshold value and decreases the diffusion level (the change of the luminance value is less likely to occur) as the maximum luminance increases. I do. This is because when the luminance of the image data is large, the luminance unevenness is originally inconspicuous. In addition, also when calculating a logical sum as a logical operation, the variable control is performed such that the threshold value increases as the maximum luminance increases. On the other hand, when calculating a logical product as a logical operation, variable control is performed so that the threshold value decreases as the maximum luminance increases.

  In the configuration example of FIG. 5, for example, after once setting the threshold, the threshold setting unit 22B uses the value in a fixed manner. Alternatively, the set threshold value may be fixedly used for a predetermined period, and then, when the maximum luminance is detected again by the maximum luminance detection unit 51, the threshold value may be reset. Alternatively, the threshold value may be reset each time the maximum luminance is detected by the maximum luminance detection unit 51.

  As still another example, the diffusion level may be variably controlled according to the state of the luminance of the backlight. For example, when the display device is a vehicle-mounted display, by performing PWM control to increase the brightness of the backlight during the daytime when the periphery of the display device is bright and to decrease the brightness of the backlight at nighttime when the periphery of the display device is dark, A device has been devised to improve visibility.

  FIG. 6 is a diagram illustrating a configuration example of a display device in a case where the diffusion level is variably controlled in accordance with the state of how the luminance of the backlight is set by the PWM control. In the configuration example shown in FIG. 6, the display device further includes a backlight luminance detecting unit 61. Further, the random number data generation section 20 includes a threshold value setting section 22C instead of the threshold value setting section 22.

  The backlight luminance detecting section 61 detects the state of the luminance of the backlight. For example, the backlight luminance detecting unit 61 detects whether the luminance of the backlight is set high or low by the PWM control. Alternatively, the backlight luminance detection unit 61 may actually detect the luminance of the backlight and determine whether the detected luminance is larger than a predetermined threshold.

  The threshold setting unit 22C sets the threshold according to the state of the backlight brightness detected by the backlight brightness detection unit 61 (whether the brightness of the backlight is set high or low). By variably controlling the threshold value set by the unit 22, the diffusion level is variably controlled.

  Specifically, when the XOR operation unit 34 is used as the logical operation, the threshold value setting unit 22C increases the threshold value and decreases the diffusion level when the backlight luminance is set high (change in luminance value). Is less likely to occur). Conversely, when the brightness of the backlight is set to be low, the threshold value setting unit 22C sets the threshold value to be small so that the diffusion level becomes large (the luminance value tends to change).

  In addition, when calculating the logical sum as a logical operation, the variable control is performed such that the threshold value is large when the backlight luminance is set high and the threshold value is small when the backlight luminance is set low. I do. On the other hand, when calculating a logical product as a logical operation, the threshold value is reduced when the backlight luminance is set high, and the threshold value is increased when the backlight luminance is set low. I do.

  Further, in the above-described embodiment, an example has been described in which dither processing is uniformly performed using random number data over the entire area of image data, but the present invention is not limited to this. For example, the diffusion level may be changed between a pixel at a predetermined position and all the other pixels of the image data input by the image data input unit 10. Specifically, of the entire area of the display panel, a place where pressure is likely to be applied from the structure of the housing or the like (a corner portion, a support structure portion, or the like) is known in advance, or a place where the touch panel is frequently touched. Is known in advance, the threshold set by the threshold setting unit 22 is made different between that location and other locations. That is, by increasing the diffusion level of the above-described specific portion as compared with the other portions, it is possible to make luminance unevenness less noticeable.

  In the above embodiment, an example has been described in which only the least significant bit of image data is operated with random number data, but the present invention is not limited to this. For example, when the number of bits of the image data is large, the lower few bits may be operated with random number data. In short, it suffices that the change in the luminance is kept within about several percent or less, and the above embodiment merely shows the operation of only the least significant bit as an example.

  Further, in the above embodiment, the example in which the image data is the RGB data has been described, but the present invention is not limited to this. For example, the image data may be YCbCr data or CMYK data.

  In addition, each of the above-described embodiments is merely an example of a specific embodiment for carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

DESCRIPTION OF SYMBOLS 10 Image data input part 20 Random number data generation part 21 Random number generation part 22, 22A, 22B, 22C Threshold setting part 23 Comparison part 30 Error diffusion part 34 XOR operation part 41 Black unevenness degree detection part 51 Maximum luminance detection part 61 Backlight luminance Detection unit

Claims (6)

an image data input unit for inputting image data composed of n bits;
A random number data generating unit for generating random number data comprising one bit or al,
For each pixel of the image data input by the image data input unit, a dither operation is performed by logically operating the least significant bit data of the image data and the random number data generated by the random number data generation unit. An error diffusion unit for performing processing,
The error diffusion unit,
For each pixel of the image data, the dither process is performed by performing a logical operation on the least significant bit data of the image data and the random number data of 1 bit,
The random number data generation unit includes:
A random number generating unit that generates a random number, a threshold setting unit that sets a threshold value, and whether the random number generated by the random number generating unit is larger than a threshold value set by the threshold setting unit is compared. And a comparator for generating the one-bit random number data in response to the threshold value set by the threshold value setting part, thereby changing the value of the image data by a logical operation using the random number data. A display device, which variably controls a diffusion level indicating a degree to be performed. The image processing apparatus further includes a black unevenness degree detection unit that detects a maximum luminance difference when all pixels of the image data input by the image data input unit are black data as a black unevenness degree,
The diffusion level is variably controlled by variably controlling a threshold value set by the threshold value setting unit in accordance with the black unevenness degree detected by the black unevenness degree detection unit. Display device. The image processing apparatus further includes a maximum luminance detecting unit that detects a maximum luminance of all pixels of the image data input by the image data input unit,
The display according to claim 1, wherein the diffusion level is variably controlled by variably controlling a threshold value set by the threshold value setting unit in accordance with the maximum luminance detected by the maximum luminance detection unit. apparatus. Further comprising a backlight luminance detection unit for detecting the state of the luminance of the backlight,
The spread level is variably controlled by variably controlling a threshold value set by the threshold value setting unit according to a state of the luminance of the backlight detected by the backlight luminance detection unit. 2. The display device according to 1.   The diffusion level can be varied by variably controlling a threshold value set by the threshold value setting unit with a pixel at a predetermined position among all pixels of the image data input by the image data input unit and other pixels. The display device according to claim 1, wherein the display device is controlled. A first step in which an image data input unit of the display device inputs image data composed of n bits;
A second step in which the random number data generation unit of the display device generates random number data of 1 bit;
The error diffusion unit of the display device, for each pixel of the image data input by the image data input unit, the least significant bit data of the image data and the random number data generated by the random number data generation unit And a third step of performing dither processing by performing a logical operation on
In the second step, the random number data generator includes:
A threshold is set and a random number is generated, and it is compared whether the generated random number is greater than a set threshold. A brightness unevenness control method, comprising: variably controlling a diffusion level indicating a degree of changing a value of the image data by a logical operation using the random number data.