JP2017097148A - Display device and luminance unevenness control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide "a display device and a luminance unevenness control method" capable of suppressing luminance unevenness different with devices irrelevantly to secular change and details of a video to be displayed without performing complicated control.SOLUTION: A display device comprises an error diffusion part 30 which performs dither processing by performing, for each pixel of image data consisting of n bits input by an image data input part 10, logical operation on low-order x-bit (1≤x<n) data of the image data and random number data consisting of x bits generated by a random number data generation part 20, and thus places the image data in a random state in which luminance differences from peripheral pixels are generated in places over the entire region, thereby making luminance unevenness of a specific region inconspicuous.SELECTED DRAWING: Figure 2

Description

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

  In general, in a display device such as a liquid crystal display or a plasma display, “brightness unevenness” in which the luminance of image data is partially uneven 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 significantly occurs due to a slight local pressure. In addition, in the case of an in-vehicle display, there is an environment unique to the in-vehicle environment such as contraction / expansion of the liquid crystal or the case due to room temperature, vibration, local pressure applied to the liquid crystal panel through touch operation on the touch panel, and uneven brightness tends to occur. It is an environment.

  Conventionally, in order to suppress such luminance unevenness, a method has been used in which an image display state is photographed with a camera for each product in a production line, and the luminance values of other pixels are corrected so as to match bright pixels. . However, this method has a problem that adjustment is required for each product and the tact time becomes long. In addition, since a change with time occurs in how the pressure is applied to the liquid crystal panel, there is a problem that luminance unevenness cannot be suppressed by luminance correction performed before factory shipment.

  In addition to the above, a technique that can suppress the occurrence of luminance unevenness has been proposed (see, for example, Patent Documents 1 to 3). In the liquid crystal display device described in Patent Document 1, it is identified that the specific part of the input video signal is a black image, and the part of the video signal identified as black is corrected information stored in advance in the storage unit. Correct based on The correction information stored in the storage unit is information created in advance during manufacturing inspection of the liquid crystal display device.

  In the liquid crystal display device described in Patent Document 2, the black unevenness information of the 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, the correction information for increasing the transmittance at the position where the luminance of the image to be displayed is determined to be low is generated, and based on the correction information, the transmittance of the display unit is generated. Is performed to increase the light intensity, and correction is performed 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 minimum luminance corresponding to black in the entire display screen of the liquid crystal panel, the driving voltage of the liquid crystal panel based on the image data is set to the entire display screen of the liquid crystal panel. Is corrected so that the luminance is uniformly increased by a predetermined amount. In this way, since the black display is performed in a state where the brightness of the entire display screen is higher than the brightness at the minimum brightness, it is possible to suppress the luminance unevenness particularly conspicuous when black display is performed on the entire display screen. it can.

  In order to solve the problem that a pseudo pattern which is a regular repetitive pattern is displayed when a video signal of the same level is continuously input to the video signal input terminal, it is generated in a noise generation circuit. A technique is known in which generation of a pseudo pattern is suppressed by adding noise composed of a pseudo random pulse signal to a video signal (see, for example, Patent Document 4). Also, this Patent Document 4 discloses that a noise signal is multiplied by a coefficient corresponding to the level of the input video signal to suppress a phenomenon that noise becomes conspicuous when the level of the input video signal is low. ing.

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

  However, in the liquid crystal display device described in Patent Document 1, since correction is performed based on correction information created in advance at the time of manufacturing inspection, adjustment is required for each product, and the tact time is increased. There arises a problem that luminance unevenness cannot be suppressed due to a problem or a change with time after shipment from the factory.

  On the other hand, in the liquid crystal display device described in Patent Document 2, correction information is generated based on black unevenness information detected when full-screen black display is performed on the display unit. No problem arises. However, since this is a correction method for locally increasing the transmittance of the display unit and reducing the light emission amount of the light source unit with respect to the position where the luminance of the image to be displayed is determined to be low, There is a problem in 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 luminance is uniformly corrected by a predetermined amount on the entire display screen of the liquid crystal panel, the correction position is specified and complicated control over the hardware is performed. Not necessary. However, in the case of Patent Document 3, since the correction can be applied only when the image data represents the minimum luminance corresponding to black in the entire display screen of the liquid crystal panel, there is a problem that the video that can suppress the luminance unevenness is limited. there were.

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

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

  In order to solve the above-described problems, in the present invention, for each pixel of input n-bit image data, lower x bits (1 ≦ x <n) of the image data and x bits are included. Dither processing is performed by performing a logical operation on the random number data.

  According to the present invention configured as described above, a luminance difference from the surrounding pixels is generated not only in a specific area of the input image data but also in the surrounding area, not in a state where the luminance difference from the surrounding area occurs in the entire area of the image data. Since it is in a random state, the luminance unevenness in the 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 is not changed regardless of the change in the state of the display device and the content of the displayed video. Different luminance unevenness can be suppressed for each unit. Further, since dither processing using random number data may be performed on the entire area of the image data, it is not necessary to specify a correction position by analyzing luminance or to perform complicated control on hardware.

It is a functional block diagram which shows the principal part structural example of the display apparatus by this embodiment. It is a figure which shows the specific structural example of the random number data generation part by this embodiment, and an error diffusion part. It is a figure which shows the operation example by the display apparatus of this embodiment. It is a figure which shows the structural example of the display apparatus which concerns on the modification of this embodiment. It is a figure which shows the structural example of the display apparatus which concerns on the modification of this embodiment. It is a figure which shows the structural example of the display apparatus which concerns on the modification of this 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 exemplary configuration of a main part of the display device according to the present embodiment. The display device of this embodiment is a liquid crystal display device as an example. As shown in FIG. 1, the display device of this embodiment includes an image data input unit 10, a random number data generation unit 20, and an error diffusion unit 30 as functional configurations.

  The image data input unit 10 inputs image data to be displayed on the display device from an image generation device (not shown). In the present embodiment, RGB data including R (red), G (green), and B (blue) data is input for each pixel. The image data input here is a digital signal in which R, G, and B are each composed of 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 generation unit 20 is a digital signal consisting of 1 bit.

  The error diffusion unit 30 performs dither processing by performing an operation on 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 performs logical operation on the least significant bit (LSB) data of image data and random data consisting of 1 bit for each pixel of image data (R, G, and B data). Dither processing is performed by calculation. The logical operation may be an exclusive logical sum, logical sum, or logical product.

  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. Further, 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 R, G, and B data.

  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 generator 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 that is smaller than the maximum value of the random number generated by the random number generation unit 21. In the present embodiment, the threshold setting unit 22 sets a predetermined fixed threshold.

  The comparison unit 23 compares whether or not the random number generated by the random number generation unit 21 is greater than the threshold set by the threshold setting unit 22, and generates random data consisting of 1 bit according to the comparison result. That is, the comparison unit 23 generates a value of “1” as 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 “0” when it is not larger.

  The XOR operation units 3G, 34G, and 34B respectively store 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 by the image data input unit 10. And an exclusive OR operation.

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

  FIG. 3 is a diagram illustrating an operation example by the display device of the present embodiment. FIG. 3A shows the image data input by the image data input unit 10. In this image data, luminance unevenness occurs in some areas 301. That is, there is a luminance difference with the surrounding area 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 dither processing for each pixel, the luminance of the region 301 where luminance unevenness has occurred and the other region 302 have random luminance values for each pixel. It becomes like this. That is, in a whole region of the image data, a random state in which a luminance difference with surrounding pixels occurs in some places is obtained. As a result, the luminance unevenness in the specific area 301 is less noticeable. Although the error with the surrounding pixels is diffused throughout the entire image data, it is an error of about 4% at the maximum, so it has almost no effect on the appearance.

  As described above, in the present embodiment, dither processing using random number data may be performed on the entire area of the image data. Therefore, in order to suppress luminance unevenness, a correction position (luminance unevenness occurs due to luminance analysis). It is not necessary to specify the 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 with correction data obtained in advance before shipment from the factory, so that it does not depend on a change in the state of the display device and depends on the content of the displayed video. In addition, it is possible to suppress uneven luminance unevenness 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, the threshold level set by the threshold setting unit 22 may be variably controlled to variably control the diffusion level representing the degree to which the value of the image data is changed by an operation using random number data. 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 the display device when 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 unit 20 includes a threshold setting unit 22 </ b> A instead of the threshold setting unit 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 the pixels are black is input by the image data input unit 10, the black unevenness degree detection unit 41 checks the luminance of all the pixels in the image data, The difference between the maximum brightness and the minimum brightness is detected as the degree of black unevenness.

  Here, the pixel having the maximum luminance among all the pixels is in the region 301 where the luminance unevenness occurs. On the other hand, the pixel having the minimum luminance among all the pixels is in the region 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 region 301 where the brightness unevenness is generated and the minimum brightness in the other region 302 as the black unevenness degree.

  The threshold setting unit 22A variably controls the diffusion level by variably controlling the threshold set by the threshold setting unit 22 according to the black unevenness detected by the black unevenness detection unit 41. Specifically, when the XOR operation unit 34 is used as a logical operation, the larger the degree of black unevenness, the smaller the threshold value and the greater the diffusion level (the more likely the luminance value changes). In addition, when calculating the logical sum as the logical operation, the threshold value is variably controlled so that the degree of black unevenness is large. On the other hand, when calculating a logical product as a logical operation, the threshold value is variably controlled so as to increase the degree of black unevenness.

  In the configuration example of FIG. 4, for example, the threshold setting unit 22 </ b> A uses a fixed value after setting the threshold once. Alternatively, the threshold value once set may be fixedly used for a predetermined period, and then the threshold value may be reset when the blackness degree detection unit 41 detects the blackness degree again. 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 the pixels of the image data. FIG. 5 is a diagram illustrating a configuration example of the display device when the diffusion level is variably controlled according to the maximum luminance of all the pixels of the image data. In the configuration example illustrated in FIG. 5, the display device further includes a maximum luminance detection unit 51. The random number data generation unit 20 includes a threshold setting unit 22B instead of the threshold setting unit 22.

  The maximum brightness detection unit 51 detects the maximum brightness of all the 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 detecting unit 51.

  Specifically, when the XOR operation unit 34 is used as a logical operation, the threshold value setting unit 22B increases the threshold value and decreases the diffusion level (the luminance value is less likely to change) as the maximum luminance is larger. To do. This is because when the brightness of the image data is high, the brightness unevenness is hardly conspicuous from the beginning. In addition, when calculating a logical sum as a logical operation, the threshold value is variably controlled so that the maximum luminance increases. On the other hand, when the logical product is calculated as a logical operation, the threshold value is variably controlled so that the maximum luminance increases.

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

  As yet another example, the diffusion level may be variably controlled according to the luminance state of the backlight. For example, when the display device is an in-vehicle display, by performing PWM control to increase the backlight brightness during the daytime when the display device is bright, and to lower the backlight brightness at night time when the display device is dark, The device which improves visibility is made.

  FIG. 6 is a diagram illustrating a configuration example of the display device in the case where the diffusion level is variably controlled according to the state of how the backlight luminance is set by the PWM control. In the configuration example illustrated in FIG. 6, the display device further includes a backlight luminance detection unit 61. The random number data generation unit 20 includes a threshold setting unit 22C instead of the threshold setting unit 22.

  The backlight luminance detecting unit 61 detects the luminance state of the backlight. For example, the backlight luminance detection unit 61 detects whether the luminance of the backlight is set high or low by PWM control. Alternatively, the backlight luminance detection unit 61 may actually detect the luminance of the backlight and determine whether or not the detected luminance is greater than a predetermined threshold value.

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

  Specifically, when the XOR operation unit 34 is used as a logical operation, the threshold value setting unit 22C increases the threshold value and decreases the diffusion level (changes in luminance value) when the backlight brightness is set high. Be less likely to occur). Conversely, when the backlight luminance is set low, the threshold setting unit 22C decreases the threshold value so that the diffusion level increases (the luminance value easily changes).

  Note that when calculating the logical sum as a logical operation, the threshold value is increased when the backlight brightness is set high, and the threshold value is decreased when the backlight brightness is set low. To do. On the other hand, when calculating the logical product as a logical operation, the threshold value is reduced when the backlight brightness is set high, and the threshold value is increased when the backlight brightness is set low. To do.

  Moreover, although the said embodiment demonstrated the example which performs the dither process by random number data uniformly with respect to the whole region of image data, this invention is not limited to this. For example, the diffusion level may be changed between a pixel at a predetermined position among all the pixels of the image data input by the image data input unit 10 and other pixels. Specifically, in the entire area of the display panel, the location where pressure is likely to be applied due to the housing structure etc. (corner portion, support structure portion, etc.) is known in advance, or the location is frequently touched on the touch panel. Is known in advance, the threshold value set by the threshold value setting unit 22 is made different between that part and the other part. In other words, brightness unevenness can be made less noticeable by increasing the diffusion level of the specific part as compared with other parts.

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

  Moreover, although the said embodiment demonstrated the example in case image data is RGB data, this 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 actualization in carrying out the present invention, and the technical scope of the present invention should not be construed 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 calculating part 41 Black unevenness degree detection part 51 Maximum brightness | luminance detection part 61 Backlight brightness | luminance Detection unit

Claims (8)

an image data input unit for inputting image data consisting of n bits;
a random number data generator for generating random number data consisting of x bits (1 ≦ x <n);
For each pixel of the image data input by the image data input unit, a low-order x-bit data of the image data and the random number data generated by the random number data generation unit are logically operated to obtain a dither. A display device comprising: an error diffusion unit that performs processing.   The error diffusion unit performs the dither processing by performing a logical operation on the least significant bit data of the image data and the random number data including 1 bit for each pixel of the image data. The display device according to claim 1. The random number data generator is
A random number generator for generating random numbers;
A threshold setting unit for setting a threshold;
A comparison unit for comparing whether the random number generated by the random number generation unit is greater than a threshold set by the threshold setting unit and generating the random data consisting of the 1 bit according to the comparison result; ,
3. The diffusion level representing the degree to which the value of the image data is changed by a logical operation using the random number data is variably controlled by variably controlling the threshold set by the threshold setting unit. The display device described. A black unevenness degree detection unit for detecting, as black unevenness degree, the maximum luminance difference when all the pixels of the image data input by the image data input part are black data;
4. The diffusion level is variably controlled by variably controlling a threshold set by the threshold setting unit in accordance with the black mura degree detected by the black mura degree detecting unit. Display device. A maximum brightness detection unit for detecting the maximum brightness of all pixels of the image data input by the image data input unit;
The display according to claim 3, wherein the diffusion level is variably controlled by variably controlling a threshold set by the threshold setting unit according to the maximum luminance detected by the maximum luminance detecting unit. apparatus. A backlight luminance detecting unit for detecting a backlight luminance state;
The diffusion level is variably controlled by variably controlling a threshold set by the threshold setting unit in accordance with a state of luminance of the backlight detected by the backlight luminance detecting unit. 3. The display device according to 3.   The diffusion level can be varied by variably controlling the threshold value set by the threshold value setting unit for all the pixels of the image data input by the image data input unit and the pixels at a predetermined position and other pixels. The display device according to claim 3, wherein the display device is controlled. A first step in which an image data input unit of the display device inputs image data consisting of n bits;
A second step in which the random number data generation unit of the display device generates random number data consisting of x bits (1 ≦ x <n);
The error diffusion unit of the display device includes, for each pixel of the image data input by the image data input unit, data of lower x bits of the image data and the random number data generated by the random number data generation unit. And a third step of performing a dither process by performing a logical operation on the brightness unevenness control method.