CN107845360B

CN107845360B - Display image correction method

Info

Publication number: CN107845360B
Application number: CN201711109850.5A
Authority: CN
Inventors: 杨建军
Original assignee: Anhui Lidajia Intelligent Technology Co ltd
Current assignee: Anhui lidajia Intelligent Technology Co.,Ltd.
Priority date: 2017-11-11
Filing date: 2017-11-11
Publication date: 2021-05-07
Anticipated expiration: 2037-11-11
Also published as: CN107845360A

Abstract

The embodiment of the disclosure provides a method for image correction of a display, which includes sampling sub-pixels of each color, incrementing or decrementing counters associated with the sub-pixels according to comparison between sampling values of image correction parameters and a global average value, and determining whether to adjust driving voltages of the corresponding sub-pixels according to the counter counts of the sub-pixels and the sub-pixels around the sub-pixels after the sampling is finished. The method can judge the area of the color display unevenness on the display, and improve the unevenness by the targeted adjustment of the driving voltage.

Description

Display image correction method

Technical Field

The present disclosure relates to the field of image display technology, and more particularly, to a method of image correction for a display.

Background

Various types of display panels, such as LCDs, LEDs, OLEDs, etc., are commonly included in various devices, such as computers, tablets, mobile phones, etc., today. Such displays are typically flat, ultra-thin display devices consisting of a large number of individually driven color pixels placed in front of a light source or reflector to produce an image. A color pixel typically includes a plurality of sub-pixels greater than three, each of which may be configured to display one of green, red, or blue, with each of the colors including at least one sub-pixel. In use, the lifetime of a liquid crystal display is typically around 5 years. After long-time use, parameters such as brightness, contrast, saturation and the like may change in some pixels or sub-pixels of the liquid crystal display due to various reasons such as threshold voltage drift, water ingress, high temperature, aging and the like, and even a short circuit or an open circuit may be generated to form a dead pixel. In addition, the performance curves for each color sub-pixel are not the same, and it is possible that some color sub-pixels will experience performance changes earlier or more easily than others.

Regardless of the reason for the performance variation, there is a possibility that a noticeable shading or color unevenness may occur on the display. While the display still includes a significant number of pixels that are operating properly, the problem with only a portion of the pixels may also result in the user needing to change the display. Therefore, there is still a need for a method of compensating for sub-pixels with performance changes in a low-cost software modification without replacing hardware, so as to extend the lifetime of the display.

Disclosure of Invention

Embodiments of the present disclosure are directed to solving at least some of the above-mentioned problems and provide a display image correction method that continuously displays a reference image for a predetermined correction period, the predetermined correction period being divided into a plurality of sampling periods; determining a global average value of image correction parameters of all sub-pixels of each color of red, green and blue and an individual value of the image correction parameters of each sub-pixel of each color in each sampling period, wherein the image correction parameters are changed only according to the gray level change of the sub-pixels for each color; incrementing a count value of a modification counter associated with at least one sub-pixel by one when the individual value of the at least one sub-pixel is greater than a global average value by a predetermined first reference threshold or more, the initial count value of each sub-pixel being zero; decrementing a count value of a modifier counter associated with at least one sub-pixel by one when the individual value of the at least one sub-pixel is less than the global average first reference threshold or less; and after a plurality of sampling periods, adjusting the driving voltage of at least some sub-pixels with the non-zero count values according to the count values of the counters, wherein at least one adjacent pixel comprising the sub-pixels with the non-zero count values exists around the pixel where each sub-pixel in the at least some sub-pixels with the non-zero count values is located.

The method can be automatically executed during the time when the display is idle, such as a screen saver, determines the degraded sub-pixels affecting the uniformity of the display without affecting the use of the user, and improves the display effect without affecting the compatibility of hardware or driving software by compensating the driving voltage (or current) thereof. The method can improve the display unevenness of the display in a manner of automatically correcting the driving voltage under the condition of not influencing the use of users.

In some embodiments, the image modification parameter for each sub-pixel is defined as P ═ g + C₁g³Where P is the image correction parameter, g is the gray scale value, C₁Is a constant less than 1.

In some embodiments, the drive voltage is decreased for sub-pixels with a negative counter value and increased for sub-pixels with a positive counter value.

In some embodiments, adjusting the driving voltage comprises applying the driving voltageChange of

Where sgn () is a sign function, C2 is a positive constant, N is a counter value, and M is a normalization coefficient.

In some embodiments, when the count values of all the sub-pixels in the adjacent pixels around the pixel where the sub-pixel whose count value is not zero are zero, the count value of the sub-pixel whose count value is not zero is cleared.

In some embodiments, the neighboring pixels include 8 nearest neighbor pixels around the pixel where the sub-pixel whose count value is not zero is located.

In some embodiments, the neighboring pixels include 16 next-nearest neighbor pixels surrounding each of the 8 nearest neighbor pixels.

In some embodiments, each adjusted drive voltage change of the sub-pixel is stored and updated and stored in non-volatile memory.

In some embodiments, when the reference image is not displayed, each sub-pixel is driven according to the last stored drive voltage.

In some embodiments, the sampling frequency corresponding to the plurality of sampling periods is less than the refresh frequency of the displayed reference image and is proportional to the absolute value of the last stored maximum driving voltage change of the sub-pixel.

The above embodiments of the present disclosure help to provide an image correction method that is low in cost and does not affect normal use of a user. The method can judge the area with uneven color display on the display more efficiently according to the global standard, and improves the color uniformity of the display image of the display by correspondingly adjusting the driving voltage of the area with uneven color display.

Drawings

The present disclosure provides drawings to illustrate some non-limiting examples in accordance with the principles of the present disclosure, and not to be construed as limiting in any way.

Fig. 1 is a schematic diagram showing a sub-pixel structure within a pixel.

Fig. 2 is a flow chart of method steps according to an embodiment of the present disclosure.

Detailed Description

The terms first, second, third, upper, lower, left, right, and the like do not limit the particular positions of the elements, nor do they define any direction or order of limitations. The preferred embodiments disclosed herein are to facilitate understanding only by those skilled in the art and are not intended to limit the scope of the disclosure, which includes various equivalent or alternative embodiments under the principles of the disclosed embodiments and what those skilled in the art can readily infer from the disclosure.

As shown in fig. 1, each pixel of a prior art display generally includes at least one red subpixel 10, at least one blue subpixel 11, and at least one green subpixel 12. The three color sub-pixels as a whole form a color pixel. The arrangement of the red sub-pixel 10, the blue sub-pixel 11 and the green sub-pixel 12 may be RGB arrangement or Pentile arrangement. Because of the small size of the pixels, a user viewing the display at a distance would not be able to discern the sub-pixels within the pixel, but would only see one bright spot. The RGB sub-pixels within a pixel may each have different luminance or gray levels so that the user sees different colors. For example, a user will see black when the three color grayscale values are all 0, and will see white when the three color grayscale values are all maximum (e.g., 255). Since the number of pixels may be millions or even more, it is difficult to avoid variation of parameters such as brightness, contrast, saturation, etc. of some of the pixels and sub-pixels during production or use. This will appear as uneven areas with a clear contrast to other parts in the image as viewed by the human eye, thereby affecting the user experience. The drive circuit 13 is typically a matrix drive circuit and may for example comprise an array of TFTs for providing a drive voltage and a drive current for each pixel respectively.

As shown in fig. 2, the method for display image modification begins at step S201, in which a reference image is continuously displayed for a predetermined modification period, which is divided into a plurality of sampling periods. The inverse of the sampling period is the sampling frequency. The sampling frequency should be less than the refresh frequency of the display displaying the reference image, above which the sampling will be redundant. Displaying the reference image preferably includes sequentially displaying three colors of red, green, and blue while displaying the screen saver image. Further, it is also possible to simply display a color other than three colors of red, green, and blue, for example, white, when displaying the screen saver image.

In step S202, a global average value of the image correction parameters of all the sub-pixels of each of the three colors of red, green and blue and an individual value of the image correction parameter of each sub-pixel of each color are determined in each sampling period. The individual value of the image correction parameter for the sub-pixel is preferably P ═ g + C₁g³Where P is the image correction parameter, g is the sub-pixel gray scale value or the difference between the sub-pixel gray scale value and the common reference gray scale value, C₁Is a constant less than 1 and may be negative, but not zero. C₁Different for different color sub-pixels. The image correction parameters described above can provide relatively balanced correction accuracy and detection sensitivity. Other image modification parameters may be defined by those skilled in the art depending on the particular type of display and sub-pixel. For example, P ═ (G-G) + C may be defined₁(g-G)³Where G is the reference gray value of the color sub-pixel defined in the reference image, P-G + C may also be defined for a display that is used for a longer time₁ln (g) to better conform to the function relationship of the gray scale and the use times. And respectively reading the gray values of the three RBG sub-pixels for each sub-pixel, and calculating the image correction parameter for the gray value read by each sub-pixel. Suppose that a color is sampled N times (N)>1) The individual values of the image correction parameter for each sub-pixel calculated in the N samples are added and divided by N and the number of sub-pixels, thereby calculating a global average of the sub-pixel image correction parameters.

In step S203, a counter is associated with each sub-pixel, which is zero for the initial value of each color, and it is determined whether the sub-pixel is likely to cause display unevenness based on the final count value thereof. A first reference threshold for the image modification parameter is defined, for example, when the individual value differs from the global average by more than 20% of the global average, then determining that a change in the performance of the sub-pixel requires adjusting the counter value of the counter. Specifically, when the individual value of a sub-pixel is greater than the global average value by more than a first reference threshold, the count value of the correction counter associated with the sub-pixel is incremented by one. And conversely, when the individual value of a sub-pixel is smaller than the global average value by more than the first reference threshold, the count value of the correction counter associated with that sub-pixel is decremented by one. This may for example represent the case of sub-pixels being too bright or too dark, respectively.

In step S204, after the end of the sampling period, some, but not all, of the driving voltages of the sub-pixels with the final count values different from zero are adjusted according to the final count values of the counters. In addition to the non-zero count value, the sub-pixel to be adjusted also requires that the count value of the same-color sub-pixel in at least one of the 8 nearest neighboring pixels around the sub-pixel is non-zero. Optionally, it is required that there is also a non-zero count value for the same color sub-pixels of at least one of the 16 next-nearest-neighbor pixels surrounding each of the 8 nearest-neighbor pixels. If there is no similar sub-pixel performance variation in the surrounding 24 pixels, the sub-pixel may belong to a dead pixel caused by open circuit or short circuit, and cannot be corrected by adjusting the driving voltage, or the sub-pixel may have a count value that is not zero in one or two samples due to measurement error or accidental reasons. Because other sub-pixels in the vicinity are normal, only one abnormal sub-pixel generally does not cause the display seen by the user to be uneven. Therefore, the driving voltage or current of the sub-pixels is adjusted only when there is a problem with more than two sub-pixels in the display area composed of the 25 adjacent pixels. When the count values of all the sub-pixels in the adjacent pixels of the sub-pixels with the count values not being zero are zero, the count values of the sub-pixels with the count values not being zero are cleared so as to neglect the adjustment of the driving voltage. It is also possible to set a second reference threshold value which defines the number of sub-pixels with a count value of non-zero in each display area formed by 25 adjacent pixels, and to correct the driving voltages of these sub-pixels when the number of sub-pixels with a count value of non-zero exceeds the second reference threshold value, and to use the normal driving voltages for neglecting the correction when the number of sub-pixels with a count value of non-zero is lower than the second reference threshold value.

For a sub-pixel with a positive count value, which may indicate that its brightness is too high, it is necessary to lower its driving voltage to a level lower than the other sub-pixels so that its image correction parameter differs from the global average value by less than the first reference threshold. For a sub-pixel with a negative count value, it may indicate that the brightness is not sufficient, and it is necessary to increase its driving voltage higher than the other sub-pixels in reverse. Adjusting the drive voltage may, for example, change the drive voltage

Where sgn () is a sign function, C₂Is a positive constant, N is the counter value, and M is the normalization coefficient. The choice of M can be used to select a segment on the curve of av that fits a functional relationship between brightness and drive voltage. Preferably, M may be the maximum value of the counter value N in all sub-pixels. C₂Similarly, for different colors, the driving voltage adjustment fitted according to the above formula is more suitable for display unevenness due to threshold voltage shift. Adjusting the sub-pixel driving voltage is for example achieved by adjusting the voltage applied to the sub-pixel cell by the gate or drain of the thin film transistor of the TFT array in the driving circuit 13 corresponding to the row and column in which the sub-pixel is located. Similarly, the current flowing through the sub-pixel may also be adjusted.

Considering that display non-uniformity may not develop slowly after a long usage time, each adjusted change in the driving voltage of the sub-pixels may be stored in a non-volatile memory, and the data may be updated after each change in the driving voltage. When the reference image is not displayed, such as during the power-on and sleep periods of the display, the sub-pixels are directly driven according to the last stored driving voltage, so as to avoid image correction before the user uses the image correction. The variation trend of each driving voltage change can also be stored, and the larger the change of the driving voltage is, the more serious the display unevenness may be caused by aging and the like, and at this time, the sampling frequency in the image correction needs to be properly increased so as to obtain a more accurate adjustment result. The smaller the change of the driving voltage is, the performance of each sub-pixel in the display is basically kept stable, and at the moment, the sampling frequency in the image correction can be properly reduced to save the computing resources and the power consumption. The sampling frequency can thus be chosen to be proportional to the absolute value of the stored drive voltage change.

The foregoing is illustrative of only exemplary embodiments within the principles and scope of the invention, and other equivalent embodiments, which will occur to those skilled in the art upon reading the disclosure herein, are intended to be within the scope of the invention.

Claims

1. A display image correction method is characterized by comprising the following steps:

continuously displaying the reference image in a predetermined correction period, the predetermined correction period being divided into a plurality of sampling periods;

determining a global average value of image correction parameters of all sub-pixels of each color of red, green and blue and individual values of the image correction parameters of each sub-pixel of each color in each sampling period, wherein the image correction parameters are only changed according to gray scale changes of the sub-pixels for each color;

incrementing a count value of a modification counter associated with at least one sub-pixel by one when the individual value of the at least one sub-pixel is greater than the global average by more than a predetermined first reference threshold, the initial count value of each sub-pixel being zero;

decrementing a count value of a modification counter associated with at least one sub-pixel by one when the individual value of the at least one sub-pixel is less than the global average by more than the first reference threshold; and

and after the plurality of sampling periods, adjusting the driving voltage of at least some sub-pixels with the non-zero count values according to the count values of the counter, wherein at least one adjacent pixel comprising the sub-pixels with the non-zero count values exists around the pixel where each sub-pixel in the at least some sub-pixels with the non-zero count values is located.

2. The method of claim 1, wherein the image modification parameters for each sub-pixel are defined as:

P＝g+C₁g³where P is the image correction parameter, g is the gray scale value, C₁Is a constant less than 1 but not 0.

3. A method as claimed in claim 2, characterized in that the drive voltage is decreased for sub-pixels whose counter value is negative and increased for sub-pixels whose counter value is positive.

4. The method of claim 3, wherein adjusting the drive voltage comprises varying the drive voltage

Where sgn () is a sign function, C₂Is a positive constant, N is the counter value, and M is the normalization coefficient.

5. The method of claim 1, wherein the count value of the sub-pixel having the count value different from zero is cleared when the count values of all sub-pixels in the adjacent pixels around the pixel where the sub-pixel having the count value different from zero is zero.

6. The method of claim 1, wherein the neighboring pixels comprise 8 nearest neighbors around the pixel where the sub-pixel whose count value is not zero is located.

7. The method of claim 6, wherein the neighboring pixels comprise 16 next-nearest-neighbor pixels surrounding each of the 8 nearest-neighbor pixels.

8. The method of claim 7, further comprising storing and updating the drive voltage change for each adjusted subpixel and storing in a non-volatile memory.

9. The method of claim 8, wherein each sub-pixel is driven according to a last stored drive voltage when the reference image is not displayed.

10. The method of claim 9, wherein the sampling frequency corresponding to the plurality of sampling periods is less than a refresh frequency of displaying the reference image and is proportional to an absolute value of a last stored change in the maximum driving voltage of the sub-pixel.