CN117116207A

CN117116207A - Gray scale compensation method and system

Info

Publication number: CN117116207A
Application number: CN202310488041.9A
Authority: CN
Inventors: 张耀仁; 苏懿
Original assignee: Honor Device Co Ltd
Current assignee: Honor Device Co Ltd
Priority date: 2023-04-28
Filing date: 2023-04-28
Publication date: 2023-11-24
Anticipated expiration: 2043-04-28

Abstract

The application provides a gray level compensation method and a gray level compensation system. The display screen displays a first image with a first display brightness; the image acquisition device obtains first image data; the computing device analyzes the first image data to obtain first brightness data, and determines first gray-scale compensation data according to the first brightness data. The display screen displays a second image with a second display brightness; the image acquisition device obtains second image data; the computing device analyzes the second image data to obtain second brightness data, and determines second gray-scale compensation data according to the second brightness data; the computing device generates a first gray scale compensation table according to the first gray scale compensation data and the second gray scale compensation data, and compensates the gray scales of all display brightness to target gray scales according to the first gray scale compensation table. The application can integrate the gray-scale compensation data with different display brightness to generate a group of gray-scale compensation tables, and carry out gray-scale compensation on the display screen under all display brightness, thereby improving the Mura compensation effect under different display brightness.

Description

Gray scale compensation method and system

Technical Field

The present application relates to the field of display technologies, and in particular, to a gray level compensation method and system.

Background

The speckles (Mura) are phenomena that cause various marks due to uneven brightness of the display screen. Specifically, when the user views the display screen, the user visually responds to the perceived light source with different frequencies, and further perceives a phenomenon that the color of the display screen is different. The spot removing (Demura) method can externally compensate for the Mura by sensing the electrical or optical characteristics of the pixels through an external driving circuit or device so that the gray scale of the Mura area is consistent with that of the standard area.

In general, in a Demura optical compensation process, gray-scale compensation is generally performed by determining a gray-scale compensation curve for other DBV in a mapping manner according to a gray-scale compensation curve for the maximum display brightness (Display Brightness Value, DBV).

However, since the dimming mode of the high DBV section and the dimming mode of the low DBV section are different, the Mura pattern of the high DBV section and the Mura pattern of the low DBV section are not identical, and the gray level compensation curve at the time of low DBV is determined in a mapping manner, and thus the Mura compensation effect at the time of low DBV is not good.

Disclosure of Invention

The application provides a gray level compensation method and a gray level compensation system, which can solve the problem of poor Mura compensation effect when a DBV is low.

In a first aspect, the present application provides a gray level compensation method, including: the display screen displays a first image with a first display brightness, wherein the first display brightness comprises display brightness in a Direct Current (DC) dimming mode; the image acquisition device shoots a display screen to obtain first image data, wherein the first image data comprises image data of a first image under at least one group of preset gray scales; the computing equipment analyzes the first image data to obtain first brightness data, wherein the first brightness data comprises the corresponding relation between the gray scale of the first image under the first display brightness and the screen brightness; the computing device determines first gray-scale compensation data according to the first brightness data; the display screen displays a second image with at least one second display brightness, wherein the second display brightness comprises the display brightness in a Pulse Width Modulation (PWM) dimming mode; the image acquisition device shoots the display screen to obtain second image data, wherein the second image data comprises at least one group of image data of the second image under preset gray scale corresponding to each second display brightness; the computing equipment analyzes the second image data to obtain second brightness data, wherein the second brightness data comprises the corresponding relation between the gray scale of the second image at each second display brightness and the screen brightness; the computing device determines second gray-scale compensation data according to the second brightness data; the computing equipment generates a first gray-scale compensation table according to the first gray-scale compensation data and the second gray-scale compensation data; the computing device compensates the gray scale under all display brightness to the target gray scale according to the first gray scale compensation table.

The gray level compensation method can be used for fusing gray level compensation data with different display brightness to generate a group of gray level compensation tables, carrying out gray level compensation on the display screen under all DBVs, improving the Mura compensation effect under different DBVs and having better hardware supporting capability.

In one implementation, the first luminance data includes a first gamma curve and the first gray-scale compensation data includes a first gray-scale compensation curve; the computing device determining first gray-scale compensation data from the first luminance data, comprising: the computing equipment derives a first gray level compensation curve according to the first gamma curve and a preset standard gamma curve, the first gray level compensation curve comprises a corresponding relation between each gray level and the first compensation gray level, and the first compensation gray level is used for compensating the corresponding gray level to the target gray level. By adopting the implementation mode, a specific acquisition mode of the first gray-scale compensation data is provided.

In one implementation, a computing device determines first gray-scale compensation data from first luminance data, comprising: the computing equipment carries out polynomial fitting on preset gray scales in a first gray scale interval and corresponding first compensation gray scales to obtain a first part of a first gray scale compensation curve, wherein the first gray scale interval is larger than a first gray scale threshold value; the computing equipment carries out curve fitting on at least two preset gray scales and corresponding first compensation gray scales in a second gray scale interval based on a display lookup table LUT to obtain a second part of a first gray scale compensation curve, wherein the second gray scale interval is smaller than or equal to a first gray scale threshold value and larger than or equal to a second gray scale threshold value; the computing equipment maps the gray scales in a third gray scale interval according to the second part of the first gray scale compensation curve to obtain a third part of the first gray scale compensation curve, wherein the third gray scale interval is smaller than a second gray scale threshold value; the computing device generates a first gray-scale compensation curve from the first portion of the first gray-scale compensation curve, the second portion of the first gray-scale compensation curve, and the third portion of the first gray-scale compensation curve. By adopting the implementation mode, the middle and high gray scales of the first gray scale interval, the low gray scale of the second gray scale interval and the lower gray scale of the third gray scale interval are respectively adopted to be fit with the gray scales of the interval, and the obtained first gray scale compensation curve is more accurate in compensation of the low gray scale.

In one implementation, after determining the first gray-scale compensation data according to the first luminance data, the computing device further includes: the computing equipment generates a group of second gray scale compensation tables according to the first gray scale compensation data, each gray scale corresponds to one second gray scale compensation table, and the second gray scale compensation table comprises first compensation gray scales corresponding to each gray scale under the first display brightness; the computing device burns the second gray-scale compensation table to the storage device. By adopting the implementation mode, after the first gray-scale compensation data are determined, the second gray-scale compensation table is burnt into the storage device to perform the first gray-scale compensation, and the compensation effect is also achieved under the condition that only one group of first brightness data exists.

In one implementation, the second luminance data includes a second gamma curve, and the second gray-scale compensation curve includes a second gray-scale compensation curve; the computing device determining second gray-scale compensation data from the second luminance data, comprising: the computing equipment derives a second gray level compensation curve according to the second gamma curve and a preset standard gamma curve, the second gray level compensation curve comprises a corresponding relation between each gray level and the second compensation gray level, and the second compensation gray level is used for compensating the corresponding gray level to the target gray level. By adopting the implementation mode, a specific acquisition mode of the second gray-scale compensation data is provided.

In one implementation, the computing device determines second gray-scale compensation data from the second luminance data, including: the computing equipment carries out polynomial fitting on preset gray scales in a fourth gray scale interval and corresponding second compensation gray scales to obtain a first part of a second gray scale compensation curve, wherein the fourth gray scale interval is larger than a first gray scale threshold value; the computing equipment carries out curve fitting on at least two preset gray scales and corresponding second compensation gray scales in a fifth gray scale interval based on a display lookup table LUT to obtain a second part of a second gray scale compensation curve, wherein the fifth gray scale interval is smaller than or equal to the first gray scale threshold value and larger than or equal to the second gray scale threshold value; the computing equipment maps gray scales in a sixth gray scale interval according to a second part of the second gray scale compensation curve to obtain a third part of the second gray scale compensation curve, wherein the sixth gray scale interval is smaller than a second gray scale threshold value; the computing device generates a second gray-scale compensation curve from the first portion of the second gray-scale compensation curve, the second portion of the second gray-scale compensation curve, and the third portion of the second gray-scale compensation curve. By adopting the implementation mode, the middle and high gray scales of the fourth gray scale interval, the low gray scale of the fifth gray scale interval and the lower gray scale of the sixth gray scale interval are respectively fitted in a fitting mode suitable for the gray scales of the interval, and the obtained second gray scale compensation curve is more accurate in compensation of the low gray scale.

In one implementation, a computing device generates a first gray-scale compensation table from first gray-scale compensation data and second gray-scale compensation data, comprising: the computing device generates a group of third gray scale compensation tables according to the second gray scale compensation data, each gray scale corresponds to one third gray scale compensation table, and the third gray scale compensation table comprises second compensation gray scales corresponding to each gray scale under the second display brightness. By adopting the implementation mode, the third gray level compensation table can be obtained to carry out gray level compensation under the second display brightness.

In one implementation, a computing device generates a first gray-scale compensation table from first gray-scale compensation data and second gray-scale compensation data, comprising: the computing device reads the second gray-scale compensation table from the storage device; the computing device fuses the third gray scale compensation table to the second gray scale compensation table to generate the first gray scale compensation table, the fusing including weighting, fitting and/or linear interpolation of the first compensation gray scale and the second compensation gray scale corresponding to each gray scale. By adopting the implementation mode, a group of first gray-scale compensation tables can be generated by a plurality of groups of gray-scale compensation tables corresponding to different display brightness, the first gray-scale compensation tables are effective in hardware, and the performance requirement of hardware of which part only supports one group of gray-scale compensation tables is met.

In one implementation, a computing device generates a first gray-scale compensation table from first gray-scale compensation data and second gray-scale compensation data, comprising: the computing device reads the second gray-scale compensation table from the storage device; the computing equipment analyzes the second gray-scale compensation table to obtain a first gray-scale compensation curve; the computing equipment acquires a first gray-scale compensation coefficient corresponding to the first gray-scale compensation curve; the first gray-scale compensation coefficient comprises a polynomial coefficient of a curve equation corresponding to the first gray-scale compensation curve; the computing equipment analyzes the second gray-scale compensation data to obtain a second gray-scale compensation curve; the computing equipment acquires a second gray-scale compensation coefficient corresponding to the second gray-scale compensation curve; the second gray-scale compensation coefficient comprises a polynomial coefficient of a curve equation corresponding to the second gray-scale compensation curve; the computing equipment fuses the first gray-scale compensation coefficient and the second gray-scale compensation coefficient to obtain a third gray-scale compensation coefficient; the fusion comprises the steps of weighting and/or linearly interpolating the first gray-scale compensation coefficient and the second gray-scale compensation coefficient; the computing equipment determines a third gray-scale compensation curve corresponding to the third gray-scale compensation coefficient as third gray-scale compensation data; the computing device generates a first gray-scale compensation table according to the third gray-scale compensation data. By adopting the implementation mode, the gray-scale compensation coefficients corresponding to different display brightness can be fused, more gray-scale compensation tables do not need to be generated, and the system memory is reduced.

In one implementation, the computing device compensates gray scales at all display brightness to a target gray scale according to a first gray scale compensation table, including: the computing device obtains first target display brightness of the display screen, wherein the first target display brightness comprises display brightness in a DC dimming mode; the computing equipment determines a first target gray scale corresponding to each screen brightness in a first gamma curve and a second target gray scale corresponding to each screen brightness in a second gamma curve; the computing device determines a first weight based on a correspondence of the first target display brightness and the first display brightness, and determines a second weight based on a correspondence of the first target display brightness and the second display brightness; the computing equipment determines a first fusion gray scale according to the product of the first target gray scale and the first weight and the sum of the product of the second target gray scale and the second weight; the computing equipment determines a first target gamma curve according to each first fusion gray level and the screen brightness corresponding to the first fusion gray level, wherein the first target gamma curve is a gamma curve corresponding to the first target display brightness; the computing equipment determines a first target gray-scale compensation curve according to the first target gamma curve; the computing equipment determines first target gray-scale compensation data according to a first target gray-scale compensation curve; the computing device fuses the first target gray-scale compensation data to a first gray-scale compensation table; and the computing equipment compensates the gray scale under all display brightness to the target gray scale according to the fused first gray scale compensation table. According to the implementation mode, in the process of software debugging of the Mura, the display brightness in the DC dimming mode is obtained based on the principle that the Mura forms of the same screen brightness are consistent, target compensation data in multiple groups of display brightness are obtained, and the target compensation data are fused into a group of first gray level compensation tables, so that the performance requirements of hardware are met.

In one implementation, the computing device compensates gray scales at all display brightness to a target gray scale according to a first gray scale compensation table, including: the computing equipment acquires second target display brightness of the display screen, wherein the second target display brightness comprises display brightness in a PWM dimming mode; the computing equipment determines first target screen brightness corresponding to each gray scale in a first gamma curve and second target screen brightness corresponding to each gray scale in a second gamma curve; the computing device determines a first weight based on a correspondence of the second target display brightness and the first display brightness, and determines a second weight based on a correspondence of the second target display brightness and the second display brightness; the computing equipment determines first fusion screen brightness according to the product of the first target screen brightness and the first weight and the sum of the product of the second target screen brightness and the second weight; the computing equipment generates a second target gamma curve according to each gray level and the brightness of the first fusion screen corresponding to each gray level, wherein the second target gamma curve is a gamma curve corresponding to the second target display brightness; the computing equipment determines a second target gray-scale compensation curve according to the second target gamma curve; the computing equipment determines second target gray-scale compensation data according to a second target gray-scale compensation curve; the computing device fuses the second target gray-scale compensation data to the first gray-scale compensation table; and the computing equipment compensates the gray scale under all display brightness to the target gray scale according to the fused first gray scale compensation table. According to the implementation mode, in the process of software debugging of Mura, target compensation data under multiple groups of display brightness are obtained based on the principle of compensating the same gray scale for the display brightness under the PWM dimming mode, and the target compensation data are fused into a group of first gray scale compensation tables to meet the performance requirements of hardware.

In a second aspect, the present application also provides a gray scale compensation system, including: the image generation device is used for displaying a first image by the display screen at a first display brightness, wherein the first display brightness comprises display brightness in a Direct Current (DC) dimming mode; the image acquisition device is used for shooting the display screen to obtain first image data, and the first image data comprises image data of a first image under at least one group of preset gray scales; the computing equipment is used for analyzing the first image data to obtain first brightness data, wherein the first brightness data comprises the corresponding relation between the gray scale of the first image under the first display brightness and the screen brightness; the computing device is further used for determining first gray-scale compensation data according to the first brightness data; the image generating device is also used for displaying a second image by the display screen with at least one second display brightness, wherein the second display brightness comprises the display brightness in a Pulse Width Modulation (PWM) dimming mode; the image acquisition device is also used for shooting the display screen to obtain second image data, and the second image data comprises at least one group of image data of the second image under preset gray scale corresponding to each second display brightness; the computing equipment is also used for analyzing the second image data to obtain second brightness data, wherein the second brightness data comprises the corresponding relation between the gray scale of the second image under each second display brightness and the screen brightness; the computing device is further used for determining second gray-scale compensation data according to the second brightness data; the computing device is further used for generating a first gray-scale compensation table according to the first gray-scale compensation data and the second gray-scale compensation data; the computing device is further used for compensating the gray scale under all display brightness to the target gray scale according to the first gray scale compensation table.

The gray level compensation system can be used for fusing gray level compensation data of different screen brightness to generate a group of gray level compensation tables, performing gray level compensation under all DBVs on the display screen, and improving Mura compensation effects under different DBVs.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a schematic diagram of a Mura morphology;

FIG. 2 is a schematic diagram of a Demura method optical compensation scenario;

FIG. 3 is a schematic diagram of a gamma curve;

FIG. 4 is a schematic diagram of a gray scale compensation curve;

FIG. 5A is a Mura pattern with a DBV of 1608 and a corresponding screen brightness of 0.29nit and a corresponding gray scale of 32 levels;

FIG. 5B is a Mura pattern with a DBV of 3515 and a corresponding screen brightness of 0.29nit and a corresponding gray scale of 16 levels;

FIG. 6A is a Mura pattern with a DBV of 266 and a corresponding screen brightness of 0.064nit and a corresponding gray scale of 32 levels;

FIG. 6B is a Mura pattern with a DBV of 681 and a corresponding screen brightness of 0.064nit and a corresponding gray scale of 16 levels;

FIG. 7A is a Mura morphology with DBV of 1 and corresponding gray scale of 32 levels;

FIG. 7B is a Mura pattern with a DBV of 266 and a corresponding gray level of 32;

FIG. 8 is a schematic diagram of a gray scale compensation system according to an embodiment of the present application;

FIG. 9 is a first flowchart of a gray level compensation method according to an embodiment of the present application;

FIG. 10 is a schematic diagram of a DBV interval according to an embodiment of the present application;

FIG. 11 is a schematic diagram of a gamma curve provided by an embodiment of the present application;

FIG. 12 is a schematic diagram of a gray scale compensation curve according to an embodiment of the present application;

FIG. 13 is a second flowchart of a gray level compensation method according to an embodiment of the present application;

FIG. 14 is a schematic view of various portions of a first gray level compensation curve according to an embodiment of the present application;

FIG. 15 is a third flowchart of a gray level compensation method according to an embodiment of the present application;

FIG. 16 is a diagram showing the second gray scale compensation scheme according to the embodiment of the present application;

FIG. 17 is a fourth flowchart of a gray level compensation method according to an embodiment of the present application;

FIG. 18 is a fifth flowchart of a gray level compensation method according to an embodiment of the present application;

fig. 19 is a sixth flowchart of a gray level compensation method according to an embodiment of the present application.

Detailed Description

The technical solutions of the embodiments of the present application will be clearly described below with reference to the drawings in the embodiments of the present application.

In the description of the present application, "/" means "or" unless otherwise indicated, for example, A/B may mean A or B. "and/or" herein is merely an association relationship describing an association object, and means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. Furthermore, "at least one" means one or more, and "a plurality" means two or more. The terms "first," "second," and the like do not limit the number and order of execution, and the terms "first," "second," and the like do not necessarily differ.

In the present application, the words "exemplary" or "such as" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "such as" is intended to present related concepts in a concrete fashion.

The terminology used in the description of the embodiments of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application, as will be described in detail with reference to the accompanying drawings.

The speckles (Mura) are phenomena that cause various marks due to uneven brightness of the display screen. Specifically, when the user views the display screen, the user visually responds to the perceived light source with different frequencies, and further perceives a phenomenon that the color of the display screen is different.

The screen brightness (luminence) is a physical quantity of the luminous intensity of the surface of the luminous object, and the unit is nit (nit). Screen brightness is an important indicator for measuring the screen luminous intensity of a display screen.

Gray scale refers to the level of the electromagnetic wave radiation intensity of the ground object, which is represented by the shade of the black-and-white image, and generally, the screen brightness change between the brightest and darkest is divided into 0-255 levels, so as to control the screen brightness of the signal input.

The screen brightness is adjusted by the display brightness (Display Brightness Value, DBV), and thus, the screen brightness may have a one-to-one correspondence with the DBV.

Illustratively, the adjustment interval of the DBV is set to [0, 3515], which can be used to adjust the screen brightness interval of [0nit,500nit ]. When the light is strong, the user can adjust the DBV to 3515 so that the user can adjust the screen brightness of the display screen to 500nit, and the display content can be seen clearly. When the light is weak, the user can adjust the DBV to 50 so as to enable the user to adjust the screen brightness of the display screen to 20nit, and the phenomenon that eyes of the user are pricked due to overlarge difference between the ambient light and the screen brightness of the display screen is avoided.

Here, the correspondence between the specific values of the DBV and the screen brightness shown in the embodiment of the present application is only for exemplary illustration, and does not constitute a specific limitation on the actual correspondence between the DBV and the screen brightness.

The ideal state of the display screen is that the gray scale has consistency under a certain DBV. However, gray scale inconsistencies are caused by the presence of Mura. For example, the display screen displays a pure color image completely consistent under each area, and when the screen brightness corresponding to the DBV is 500nit, the gray scale corresponding to each pixel should be 128 levels, however, the gray scale actually corresponding to some pixels in the Mura area may be 32 levels or 64 levels, which has a problem that the screen brightness of the display screen is not uniform.

FIG. 1 is a schematic representation of the Mura morphology.

As shown in fig. 1, taking an Organic Light-Emitting Diode (OLED) screen as an example, among low-temperature polysilicon thin film transistors (Low Temperature Poly-Silicon ThinFilm Transistor, LTPS TFTs) fabricated on a large-area glass substrate due to limitations of crystallization process, TFTs at different positions generally have non-uniformity in electrical parameters such as threshold voltage, mobility, etc., which are converted into current and brightness differences of the OLED screen and are perceived by human eyes, i.e., mura phenomenon.

For example, the area a is a local area of the display screen, in an ideal state, the whole area a should keep consistent with the gray level of the standard area A1, in fact, the gray level of the area A2 in the area a is obviously higher than the gray level of the area A1, the gray level of the area A3 is obviously lower than the gray level of the area A1, and the uneven brightness phenomenon of the area A2 and the area A3 is Mura. Specifically, the A2 region and the A3 region each include a plurality of irregular plaques as shown in the A4 region. The plaque is the morphology of Mura. The A2 region and the A3 region are Mura regions formed by a plurality of plaque shapes. The Mura area is different from the A1 standard area in gray scale. The Mura may be identified by switching to a black frame in the darkroom, and other low gray scale frames, and then observing different process defects from different observation angles, such as lateral stripes, forty-five degree stripes, or irregular patches. Fig. 1 illustrates a plaque-like process defect.

The spot removing (Demura) method can externally compensate for the Mura by sensing the electrical or optical characteristics of the pixels through an external driving circuit or device so that the gray scale of the Mura area is consistent with that of the standard area. External compensation includes electrical compensation and optical compensation. Among them, optical compensation is a common compensation method.

Fig. 2 is a schematic diagram of a Demura method optical compensation scenario.

As shown in fig. 2, the Demura method may be implemented using an image generator, a complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor, CMOS) camera or a charge coupled device (Charge Coupled Device, CCD) camera, a computing device, and a device stage.

For example, the optical compensation procedure of the Demura method may include:

step S1, a display screen to be detected is placed on a device carrying platform, and an external pin of the display screen is connected with an image generator, so that the image generator inputs standard image signals to the display screen, and an image to be detected under a certain DBV is displayed on the display screen. The image to be measured may be a grayscale image or an RGB color mode (Red Green Blue Color Mode) image.

And S2, acquiring image data of the image to be detected under a plurality of gray scales by using a CMOS camera or a CCD camera, and transmitting the image data to the computing equipment.

Step S3, the computing equipment receives the image data, obtains gray-scale compensation data of the image data through a Demura compensation algorithm, and burns the compensation data into a Flash memory (Flash ROM) to eliminate Mura of the display screen.

FIG. 3 is a schematic diagram of a Gamma curve.

As shown in fig. 3, a standard gamma curve K1 and an actual gamma curve K2 are shown.

The gamma value can be determined by the correspondence of gray scale to screen brightness. Since the Mura phenomenon is accompanied by a change in the range of gamma values, the demux compensation algorithm involves a back-pushing process of the gamma curve to determine the gray level that the Mura region needs to compensate for.

In the specific implementation process of step S3, the computing device can analyze the screen brightness of the image to be tested under a certain DBV and a plurality of gray scales corresponding to the DBV according to the image data. Because the camera does not capture image data at all gray scales based on time cost considerations, the computing device needs to fit a gray scale-screen brightness curve for each pixel by an algorithm according to the screen brightness at several gray scales to obtain the screen brightness at other gray scales. The gray-screen brightness curve is the actual gamma curve K2. The calculation device may be adapted to fit the actual gamma curve K2 by using an algorithm commonly used in the art, which will not be described in detail in the present application.

The standard gamma curve K1 is usually preset in the computing device, and after the actual gamma curve K2 is determined, since the actual gamma curve K2 deviates from the standard gamma curve K1, a gray-scale compensation curve needs to be constructed by a Demura compensation algorithm. The Demura compensation algorithm is a common algorithm in the art, and this will not be described in detail in the present application.

FIG. 4 is a schematic diagram of a gray level compensation curve.

As shown in fig. 4, the computing device reversely derives the gray scale corresponding to the fitted gray scale-screen brightness curve according to the standard screen brightness corresponding to the gray scale in the standard gamma curve K1, so as to obtain the compensation gray scale corresponding to each gray scale, and generate the gray scale compensation curve D1. The compensation gray scale may be used to compensate each gray scale to a target gray scale, so that the compensated gray scale reaches the brightness in the standard gamma curve K1.

Under ideal conditions, image acquisition is required for each DBV, and the Demura method in the process is required to be executed, so that all DBVs can achieve the optimal gray level compensation effect. However, since the actual application scenario of the display screen involves a larger DBV interval, and the medium-and-large-sized OLED display screen has a large number of pixels, if image acquisition is performed for each DBV, a large amount of time is consumed, and the computing device faces higher memory resource overhead and is unfavorable for processing of subsequent algorithms. Therefore, in general, the Demura method collects only image data of one maximum DBV, and performs 0-255 full gray level compensation by the image data of the DBV.

In this way, the computing device can construct a gray-scale compensation curve for the image data of the maximum DBV, and obtain gray-scale compensation curves corresponding to other DBVs through the gray-scale compensation curve mapping. For example, the gray-scale compensation curve for the DBV 3515 can be mapped to the gray-scale compensation curve for the DBV 1608.

The gray level compensation curve is constructed by the image data when the maximum DBV is selected, and the brighter the image to be detected is, the more gray levels can be displayed as the screen brightness corresponding to the DBV is larger. Therefore, mura at the maximum screen brightness corresponding to the maximum DBV has a certain significances.

However, the gray level compensation method is a mapping compensation based on the default maximum DBV matching with the Mura pattern of the low DBV. In fact, the maximum DBV and the low DBV generally correspond to different dimming modes, and Mura modes of the two dimming modes are not consistent, and the low DBV is mapped and compensated by the gray level compensation curve obtained by the maximum DBV, which results in poor compensation effect at the time of low DBV.

The DBV is determined by the voltage difference between the two ends of the light emitting diode of the display screen, and the adjustment of the DBV is actually to adjust the voltage difference between the two ends of the light emitting diode of the display screen. Typically, there are two DBV dimming modes.

The first DBV dimming mode is a Direct Current (DC) dimming mode. The DC dimming mode is to change the DBV of the display screen by increasing or decreasing the circuit power. The larger the DBV is, the larger the circuit power is, and the brighter the corresponding screen brightness is; the smaller the DBV, the less circuit power and the darker the corresponding screen brightness. In the DC dimming mode, mura can be very severe at low power, resulting in a muster screen, and thus, the DC mode is generally suitable for high DBV intervals.

The second DBV dimming mode is a pulse width modulation (Pulse Width Modulation, PWM) dimming mode. The PWM dimming mode is to control the display screen to flicker and alternate on a certain frequency, and the effect of continuous display is achieved by utilizing the visual residual effect of human eyes. The larger the DBV is, the faster the flicker alternation frequency of the display screen is, and the brighter the corresponding screen brightness is; the smaller the DBV, the slower the frequency of display screen flicker alternation, and the darker the corresponding screen brightness. Since the low-frequency PWM dimming has a good display effect, the PWM dimming mode is generally applied to a low DBV range.

The morphology of the high DBV interval and the low DBV interval Mura is different.

Fig. 5A is a Mura pattern with a DBV 1608 and a corresponding screen brightness of 0.29nit and a corresponding gray scale of 32 levels.

Fig. 5B is a Mura pattern with a DBV of 3515 and a corresponding screen brightness of 0.29nit and a corresponding gray scale of 16 levels.

As shown in fig. 5A and 5B, the high DBV interval corresponding to the DC dimming mode is exemplified as [1291, 3515 ]. In the high DBV section, when the same screen brightness is achieved, the Mura forms corresponding to different DBVs are consistent. Therefore, the method is suitable for a Demura method in which mapping compensation is performed on a gray-scale compensation curve obtained by the maximum DBV.

Fig. 6A is a Mura pattern with a DBV of 266 and a corresponding screen brightness of 0.064nit and a corresponding gray level of 32.

Fig. 6B is a Mura pattern with a DBV of 681 and a corresponding screen brightness of 0.064nit and a corresponding gray scale of 16 levels.

As shown in fig. 6A and 6B, the low DBV interval corresponding to the PMW dimming mode is exemplified as [0, 1291 ]. In the low DBV section, the Mura forms corresponding to different DBVs are not consistent when the same screen brightness is achieved.

Fig. 7A shows Mura morphology when DBV is 1 and the corresponding gray level is 32 levels.

Fig. 7B shows Mura morphology with a DBV of 266 and a corresponding gray level of 32.

As shown in fig. 7A and 7B, the low DBV interval corresponding to the PMW dimming mode is exemplified as [0, 1291 ]. In the low DBV section, the Mura forms corresponding to different DBVs are not consistent at the same gray level.

That is, in the high DBV section, the morphology of Mura is predictable, but in the low DBV section, the morphology of Mura is not obvious and is difficult to predict, both at the same screen brightness and at the same gray level, so that the Demura method of mapping compensation by the gray level compensation curve obtained by the maximum DBV is not suitable for the low DBV section, and the demra method has poor compensation effect for the low DBV section, and the Mura of the display screen cannot be eliminated at the low DBV.

In summary, in the prior art, for gray level compensation of a low DBV, image acquisition and analysis are not performed for the low DBV based on consideration of time cost, but gray level compensation is performed for Mura of the low DBV by a mapping method, however, since Mura forms of a high DBV section and a low DBV section are inconsistent, a compensation effect of a degra method for the low DBV section is not good in general, and Mura of a display screen cannot be eliminated under the low DBV.

In order to solve the above problems, an embodiment of the present application provides a gray level compensation method.

Fig. 8 is a schematic diagram of a gray scale compensation system according to an embodiment of the present application. The gray level compensation method provided by the embodiment of the application can be realized based on the gray level compensation system.

As shown in fig. 8, the gray-scale compensation system 100 includes:

the image generating device 10, the image generating device 10 is used for connecting with an external pin of the display screen 200, and inputting a standard image signal to the display screen 200, so that the display screen 200 displays an image under the DBV.

The image acquisition device 11, the image acquisition device 11 is used for shooting the display screen to obtain image data.

The computing device 12 is used for receiving the image data sent by the image acquisition device and analyzing the image data to obtain gray-scale compensation data.

The storage device 13 is used for receiving the gray-scale compensation data stored by the computing device 12, reading the gray-scale compensation data by using a display driver corresponding to the display screen, and eliminating Mura of the display screen.

The computing device in embodiments of the present application may be, for example, a personal computer, a server, a tablet (portable android device, PAD), a personal digital assistant (personal digital assistant, PDA), a handheld computing device, an industrial computing device, or the like.

Fig. 9 is a first flowchart of a gray level compensation method according to an embodiment of the present application.

As shown in fig. 9, the gray-scale compensation method includes steps S11 to S20.

In step S11, the display screen displays a first image with a first DBV, which includes a DBV in a direct current DC dimming mode.

In some embodiments, the display screen may be connected to the image generator, receive a standard image signal input from the image generator, and display the first image at the first DBV. The first image may be a grayscale image or an RGB color mode image.

Fig. 10 is a schematic diagram of a DBV interval according to an embodiment of the present application.

As shown in fig. 10, a node T1 for dividing a high DBV section corresponding to the DC mode and a low DBV section corresponding to the PWM is preset in the DBV section of the display screen. Illustratively, the DBV interval is [0, 3515], the preset node T1 is at 1291 for DBV, thus the low DBV interval is [0, 1291], and the high DBV interval is [1291, 3515]. Taking the screen brightness interval corresponding to the DBV interval as [0nit,500nit ] as an example, when the first DBV is 3515, the corresponding screen brightness is 500nit.

Accordingly, the display screen displays the first image at the first DBV of 3515, which corresponds to displaying the first image at 500nit.

It should be noted here that the values of the screen brightness are only for illustrative purposes, and the selection of the screen brightness is based on the own performance of the display screen. In the embodiment of the present application, the dimming mode is only exemplified by a mixed dimming mode of a DC dimming mode and a PWM dimming mode, and in particular, other dimming modes may be adopted, which is not limited by the embodiment of the present application.

Step S12, the image acquisition device shoots the display screen to obtain first image data, wherein the first image data comprises image data of a first image under at least one group of preset gray scales.

In some embodiments, the image capture device may be a CMOS camera or a CCD camera. The choice of camera resolution depends on the resolution of the detected panel, the size, the shooting distance and the accuracy of the Demura compensation. Since the setting of the camera itself is critical for accurate acquisition of data, the camera needs to be debugged before image acquisition to remove the unevenness caused by the camera. For example, to make usual corrections. After debugging, the image acquisition device shoots the display screen under a plurality of preset gray scales. For example, the preset gray scale may include: 16-level gray scale, 32-level gray scale, 64-level gray scale, and 128-level gray scale.

After the image acquisition device acquires the first image data, the first image data is sent to the computing equipment.

In step S13, the computing device parses the first image data to obtain first luminance data, where the first luminance data includes a correspondence between a gray scale of the first image at the first display luminance and a screen luminance.

FIG. 11 is a schematic diagram of a gamma curve according to an embodiment of the present application.

As shown in fig. 11, the computing device analyzes the first image data, and can obtain the screen brightness corresponding to each pixel of the first image under the preset gray scale. For example, the computing device may obtain a screen luminance of 50nit for the first pixel when the preset gray level is 16, a screen luminance of 70nit for the preset gray level is 32, a screen luminance of 100nit for the preset gray level is 64, and may obtain a screen luminance of 55nit for the second pixel when the preset gray level is 16, a screen luminance of 75nit for the preset gray level is 32, and a screen luminance of 110nit for the preset gray level is 64. After the computing device obtains the screen brightness corresponding to each pixel under the preset gray scale, the computing device can obtain a first gamma curve Q1 based on the fitting of the corresponding relation between the preset gray scale and the screen brightness, so that the computing device can obtain the corresponding relation between all the gray scales and the screen brightness in a fitting mode, and the corresponding relation between all the gray scales and the screen brightness is stored as first brightness data. That is, the first gamma curve Q1 corresponding to each pixel is included in the first luminance data. The embodiment of the application is exemplified by a gamma curve corresponding to only one pixel.

Specifically, the numerical analysis has various curve fitting modes, such as polynomial fitting, exponential fitting, gaussian fitting and the like, wherein the polynomial fitting programming is simple to realize and has clear meaning. The fitting modes in the embodiments of the present application are all exemplified by polynomial fitting. In the practical application process, other curve fitting modes can be adopted, and the application is not repeated.

In step S14, the computing device determines first gray-scale compensation data according to the first luminance data.

Fig. 12 is a schematic diagram of a gray-scale compensation curve according to an embodiment of the present application.

As shown in fig. 12, in some embodiments, the computing device may iteratively solve the first gamma curve Q1 according to Python language, so as to obtain a first gray-scale compensation curve F1.

As further shown in fig. 11 and fig. 12, in some embodiments, the computing device derives a first gray-scale compensation curve F1 according to the first gamma curve Q1 and a preset standard gamma curve R1. The first gray level compensation curve F1 includes a corresponding relationship between each gray level and a first compensation gray level, where the first compensation gray level is used for compensating the corresponding gray level to the target gray level.

The first gray-scale compensation curve F1 may be represented by a polynomial. The computing device may derive the first gray-scale compensation curve F1 from the first gamma curve Q1 through various program algorithms, which is not limited in the embodiment of the present application, and the embodiment of the present application will not be repeated.

For example, the first gray-scale compensation curve F1 may be y ₁ ＝a ₁ x ³ +b ₁ x ² +c ₁ x+d ₁ 。

Wherein x represents gray scale, y ₁ Representing a first compensation gray scale, a ₁ 、b ₁ 、c ₁ 、d ₁ The polynomial coefficients of the first gray-scale compensation curve F1. The first gray level compensation curve F1 may be obtained based on a conventional Demura compensation algorithm.

Fig. 13 is a second flowchart of a gray level compensation method according to an embodiment of the present application.

As shown in fig. 13, step S14 includes steps S141 to S144.

Fig. 14 is a schematic diagram of each portion of a first gray level compensation curve according to an embodiment of the present application.

S141, the computing device performs polynomial fitting on the preset gray scale in the first gray scale interval and the corresponding first compensation gray scale to obtain a first part F11 of the first gray scale compensation curve F1, wherein the first gray scale interval is larger than a first gray scale threshold value.

The first gray level threshold is, for example, 32 gray levels.

The gray scales above 32 levels are middle and high gray scales, the difference between different batches of screens is small, and the first part F11 of the first gray scale curve F1 obtained by polynomial fitting in the first gray scale interval has a good Mura compensation effect.

S142, the computing device performs curve fitting on at least two preset gray scales and corresponding first compensation gray scales in a second gray scale interval based on a Look-Up Table (LUT) to obtain a second part F12 of the first gray scale compensation curve F1, wherein the second gray scale interval is smaller than or equal to the first gray scale threshold value and larger than or equal to the second gray scale threshold value.

The second gray level threshold is, for example, 12 gray levels.

The gray scales of 12-32 levels are low gray scales, and at least two preset gray scales and corresponding first compensation gray scales are stored in the LUT in the second gray scale interval, so that the fitted curve is closer to the actual value of the first compensation gray scales.

S143, the computing device maps the gray scale in the third gray scale interval according to the second portion F12 of the first gray scale compensation curve F1 to obtain a third portion F13 of the first gray scale compensation curve F1, wherein the third gray scale interval is smaller than the second gray scale threshold.

The gray levels below 12 levels are lower gray levels, and the image acquisition device cannot acquire the gray level of the third gray level interval under the performance limitation, so that the third portion F13 of the first gray level compensation curve F1 can predict according to the second portion F12 of the first gray level compensation curve F1, and Mura compensation in the third gray level interval is more accurate.

S144, the computing device generates a first gray-scale compensation curve F1 according to the first portion F11 of the first gray-scale compensation curve F1, the second portion F12 of the first gray-scale compensation curve F1 and the third portion F13 of the first gray-scale compensation curve.

The computing device can determine the first gray-scale compensation curve F1 as first gray-scale compensation data. The first gray-scale compensation data may be discrete data points in a plurality of gray-scale compensation tables, or may exist in a polynomial form in the program. The embodiment of the application only uses a gray level compensation curve corresponding to one pixel for illustration.

The steps S11 to S14 may be completed before the display screen leaves the factory, or may be performed at any other time period. The steps can be independently operated when only one group of first gray-scale compensation data exists, so that the general compensation effect is achieved.

In step S15, the display screen displays a second image with at least one second DBV, the second DBV including a DBV in a pulse width modulation PWM dimming mode.

As further shown in fig. 10, the second DBV may be a DBV in the low DBV interval [0, 1291 ]. Taking the screen brightness interval corresponding to the DBV interval as [0nit,500nit ] as an example, when the second DBV is 100, the corresponding screen brightness is 10nit, and when the second DBV is 200, the corresponding screen brightness is 50nit.

Therefore, the display screen displays the second image with the second DBV being 100, which corresponds to displaying the second image at 100 nit.

The display screen may display the second image in a plurality of sets of low DBV in the low DBV interval. In this way, multiple groups of second image data can be obtained for analysis subsequently, so that the Mura compensation effect of the low DBV is improved conveniently.

In step S16, the image capturing device captures a display screen to obtain second image data, where the second image data includes image data of the second image under at least one set of preset gray levels corresponding to each second DBV.

In the second image data acquisition process, the second image data under the same preset gray level as the first image data can be acquired, and the second image data can be acquired at a lower preset gray level, so that the second image data is convenient to be used for gray level compensation in a low DBV interval. For example, the preset gray scale may include: 12-level gray scale, 16-level gray scale, 18-level gray scale, 20-level gray scale, and the like.

The image acquisition device generally cannot acquire data below 12 levels of gray levels, and the preset gray level is selected from gray levels larger than 12 levels.

And after the image acquisition device acquires the second image data, the second image data is sent to the computing equipment.

In step S17, the computing device parses the second image data to obtain second luminance data, where the second luminance data includes a correspondence between a gray level of the second image under each second DBV and a screen luminance.

Further, as shown in fig. 11, taking the second image data corresponding to the two second DBVs as an example, the computing device analyzes the first second image data, so as to obtain a second gamma curve H1 corresponding to the first second DBV, and the computing device analyzes the second image data, so as to obtain a second gamma curve H2 corresponding to the second DBV.

Because the DBVs are different, the first DBV is larger than the first second DBV, and the first second DBV is larger than the second DBV, the screen brightness corresponding to each gray level in the first gamma curve Q1 is larger than the screen brightness corresponding to each gray level in the second gamma curve H1; the screen brightness corresponding to each gray level in the second gamma curve H1 is greater than the screen brightness corresponding to each gray level in the second gamma curve H2.

For example, the first gamma curve Q1 has a screen brightness of 500nit corresponding to a gray level of 255, the second gamma curve H1 has a screen brightness of 300nit corresponding to a gray level of 255, and the second gamma curve H2 has a screen brightness of 100nit corresponding to a gray level of 255.

Thus, each DBV corresponds to a different screen brightness interval, i.e., a first DBV corresponds to [0nit,500nit ], and a first second DBV corresponds to [0nit,300nit ]; the second DBV corresponds to [0nit,100nit ].

After the computing device obtains the gamma curves of the plurality of different screen brightness intervals, the computing device can be used for subsequently determining the corresponding relations between other DBVs and the gamma curves.

In step S18, the computing device determines second gray-scale compensation data according to the second luminance data.

As further shown in fig. 12, in some embodiments, the computing device derives a first second gray-scale compensation curve E1 according to the second gamma curve H1 and a preset standard gamma curve R1. The computing device derives according to the second gamma curve H2 and a preset standard gamma curve R1, and obtains a second gray-scale compensation curve E2. The second gray level compensation curve comprises a corresponding relation between each gray level and a second compensation gray level, and the second compensation gray level is used for compensating the corresponding gray level to the target gray level.

For example, the first and second gray-scale compensation curves E1 may be y ₂ ＝a ₂ x ³ +b ₂ x ² +c ₂ x+d ₂ . The second gray level compensation curve E2 can be y ₃ ＝a ₃ x ³ +b ₃ x ² +c ₃ x+d ₃ 。

Wherein x represents gray scale, y2 represents first second compensation gray scale, y3 represents second compensation gray scale, a ₂ 、b ₂ 、c ₂ 、d ₂ Polynomial coefficient, a, of the second gray-scale compensation curve E1 ₃ 、b ₃ 、c ₃ 、d ₃ The polynomial coefficient of the second gray-scale compensation curve E2. The second gray level compensation curve may be obtained based on a conventional Demura compensation algorithm.

Fig. 15 is a third flowchart of a gray level compensation method according to an embodiment of the present application.

As shown in fig. 15, step S18 includes steps S181 to S184.

S181, the computing equipment carries out polynomial fitting on preset gray scales in a fourth gray scale interval and corresponding second compensation gray scales to obtain a first part of a second gray scale compensation curve, wherein the fourth gray scale interval is larger than a first gray scale threshold value;

s182, the computing equipment performs curve fitting on at least two preset gray scales and corresponding second compensation gray scales in a fifth gray scale interval based on a display lookup table LUT to obtain a second part of a second gray scale compensation curve, wherein the fifth gray scale interval is smaller than or equal to the first gray scale threshold value and larger than or equal to the second gray scale threshold value;

S183, the computing equipment maps the gray scale in a sixth gray scale interval according to the second part of the second gray scale compensation curve to obtain a third part of the second gray scale compensation curve, wherein the sixth gray scale interval is smaller than a second gray scale threshold value;

s184, the computing device generates a second gray-scale compensation curve according to the first portion of the second gray-scale compensation curve, the second portion of the second gray-scale compensation curve, and the third portion of the second gray-scale compensation curve.

The arrangement of the first portion, the second portion, and the third portion corresponding to the first second gray-scale compensation curve E1 may refer to a specific arrangement of the first gray-scale compensation curve F1, and the second gray-scale compensation curve E2 is similar, which is not described in detail in the embodiments of the present application.

In step S19, the computing device generates a first gray-scale compensation table according to the first gray-scale compensation data and the second gray-scale compensation data.

In some embodiments, step S14 is followed by step S21-step S22.

In step S21, the computing device generates a set of second gray-scale compensation tables according to the first gray-scale compensation data, where each gray-scale corresponds to one second gray-scale compensation table, and the second gray-scale compensation table includes a first compensation gray-scale corresponding to each gray-scale under the first DBV.

FIG. 16 is a schematic diagram of a second gray level compensation scheme according to an embodiment of the present application.

As shown in fig. 16, the second gray-scale compensation table is arranged in n×m levels corresponding to the pixels of the first image. Each second gray level compensation table is a first compensation gray level corresponding to each gray level under the first DBV. Taking a second gray level compensation table for a screen with 500nit and 32 gray levels corresponding to the first DBV as an example, the first compensation gray level in the first pixel is 4, the first compensation gray level in the second pixel is 5, and the first compensation gray level in the third pixel is 3.

The second gray level compensation table records first compensation gray levels corresponding to preset gray levels in a discrete point mode, and other gray levels can generate corresponding first compensation gray levels in an interpolation, fitting or other modes in a specific application process.

In step S22, the computing device burns the second gray-scale compensation table to the storage device. By way of example, the storage device may be a Flash ROM.

In this way, the computing device may perform the first gray-scale compensation according to the second gray-scale compensation table.

In some embodiments, step S19 further comprises step S191-step S193.

In step S191, the computing device generates a set of third gray-scale compensation tables according to the second gray-scale compensation data, where each gray-scale corresponds to a third gray-scale compensation table, and the third gray-scale compensation table includes a second compensation gray-scale corresponding to each gray-scale under the second DBV.

Taking a third gray level compensation table for example when the screen brightness corresponding to the second DBV is 2nit and 32 gray levels, the second compensation gray level in the first pixel is 5, the second compensation gray level in the second pixel is 2, and the second compensation gray level in the third pixel is 1.

The third gray level compensation table records second compensation gray levels corresponding to preset gray levels in a discrete point mode, and other gray levels can generate corresponding second compensation gray levels in an interpolation, fitting or other modes in a specific application process.

In step S192, the computing device reads the second gray-scale compensation table from the storage device.

Step S192 is not limited to be performed after step S191, and in a specific implementation, the reading may be performed in any period of time before step S193, which is not limited in the embodiment of the present application.

In step S193, the computing device fuses the third gray-scale compensation table to the second gray-scale compensation table to generate the first gray-scale compensation table, the fusing including weighting, fitting, and/or linearly interpolating the first compensation gray-scale and the second compensation gray-scale corresponding to each gray-scale.

In some embodiments, if the preset gray level in the third gray level compensation table and the corresponding second compensation gray level have no repetition interval with the preset gray level in the second gray level compensation table and the corresponding first compensation gray level, the computing device may directly fuse the third gray level compensation table into the display luminance axis of the second gray level compensation table in a fitting manner to perform gray level compensation under two DBVs.

The hardware equipment can only record a group of gray level compensation tables, the computing equipment fuses two compensation gray levels corresponding to each gray level of each pixel under at least two DBVs into one compensation gray level and records the compensation gray level into the first gray level compensation table, and the accuracy of the compensation gray level corresponding to the low DBV is improved while the hardware capability is met.

Fig. 17 is a fourth flowchart of a gray level compensation method according to an embodiment of the present application.

As shown in fig. 17, step S19 includes steps S1911 to S1918.

In step S1911, the computing device reads the second gray-scale compensation table from the storage device.

This step can be referred to as step S192.

In step S1912, the computing device parses the second gray-scale compensation table to obtain the first gray-scale compensation curve.

The second gray-scale compensation table is actually a plurality of compensation tables having discrete points, and the first gray-scale compensation curve cannot be directly obtained from the second gray-scale compensation table, so that the discrete points need to be analyzed to obtain the first gray-scale compensation curve.

In step S1913, the computing device obtains a first gray-scale compensation coefficient corresponding to the first gray-scale compensation curve, where the first gray-scale compensation coefficient includes a polynomial coefficient of a curve equation corresponding to the first gray-scale compensation curve.

For example, the first gray-scale compensation curve F1 may be y ₁ ＝a ₁ x ³ +b ₁ x ² +c ₁ x+d ₁ The first gray-scale compensation coefficient is a ₁ 、b ₁ 、c ₁ D ₁ 。

In step S1914, the computing device parses the second gray-scale compensation data to obtain a second gray-scale compensation curve.

The second gray-scale compensation data can exist in a program form, and the second gray-scale compensation curve can be obtained by analyzing the second gray-scale compensation data.

In step S1915, the computing device obtains a second gray-scale compensation coefficient corresponding to the second gray-scale compensation curve, where the second gray-scale compensation coefficient includes a polynomial coefficient of a curve equation corresponding to the second gray-scale compensation curve.

Exemplary, a first and a second gray-scale compensation curve E1 may be y ₂ ＝a ₂ x ³ +b ₂ x ² +c ₂ x+d ₂ . The second gray level compensation curve E2 can be y ₃ ＝a ₃ x ³ +b ₃ x ² +c ₃ x+d ₃ The first and second gray-scale compensation coefficients are a ₂ 、b ₂ 、c ₂ D ₂ A second gray-scale compensation coefficient is a ₃ 、b ₃ 、c ₃ D ₃ 。

In step S1916, the computing device fuses the first gray-scale compensation coefficient and the second gray-scale compensation coefficient to obtain a third gray-scale compensation coefficient, where the fusing includes weighting, fitting, and/or linearly interpolating the first gray-scale compensation coefficient and the second gray-scale compensation coefficient.

For example, respectively will a ₁ 、a ₂ 、a ₃ Weighting to obtain a ₀ Will b ₁ 、b ₂ 、b ₃ Weighting to obtain b ₀ C, adding ₁ 、c ₂ 、c ₃ Weighting to obtain c ₀ And d ₁ 、d ₂ 、d ₃ Weighting to obtain d ₀ I.e. the third gray-scale compensation coefficient is a ₀ 、b ₀ 、c ₀ 、d ₀ 。

In step S1917, the computing device determines a third gray-scale compensation curve corresponding to the third gray-scale compensation coefficient as the third gray-scale compensation data.

For example, the computing device may determine a third gray scale curve as y based on the third gray scale compensation coefficient ₀ ＝a ₀ x ³ +b ₀ x ² +c ₀ x+d ₀ 。

In step S1918, the computing device generates a first gray-scale compensation table according to the third gray-scale compensation data.

The computing device can determine the compensation gray scale corresponding to each gray scale according to the third gray scale data, and a first gray scale compensation table under each gray scale is obtained.

In step S20, the computing device compensates the gray scales under all DBV to the target gray scale according to the first gray scale compensation table.

Fig. 18 is a fifth flowchart of a gray level compensation method according to an embodiment of the present application.

As shown in fig. 18, step S19 includes steps S201 to S209.

In step S201, the computing device obtains a first target DBV of the display screen. The first target DBV includes a DBV in a DC dimming mode.

The first gray-scale compensation table can be configured in hardware, and is further adjusted during software operation to realize gray-scale compensation under all DBVs.

In step S202, the computing device determines a first target gray level corresponding to each of the screen brightnesses in the first gamma curve and a second target gray level corresponding to each of the screen brightnesses in the second gamma curve.

And under the DC dimming mode, the corresponding Mura forms are consistent when the brightness of the screen is the same, and the gamma curves corresponding to other DBVs are obtained between the first gamma curve and the second gamma curve in at least one mode of interpolation, weighting and fitting based on the principle. For example, when the screen brightness is 100nit, the first target gray level corresponding to the first gamma curve is 32 levels, and the second target gray level corresponding to the second gamma curve is 64 levels.

In step S203, the computing device determines a first weight based on the correspondence between the first target DBV and the first DBV, and determines a second weight based on the correspondence between the first target DBV and the second DBV.

The first target DBV is 1500, the first DBV is 1600, and the second DBV is 100, for example. Thus, the first weight may be determined based on the proportional relationship of the first target DBV to the first DBV, i.eThe second weight can be determined from the proportional relation of the target DBV to the second DBV, i.e. +.>/>

The embodiment of the application only carries out the exemplary explanation on the determination mode of the first weight and the second weight, the first weight and the second weight are not limited to the uniformly distributed proportional relation, and the first weight and the second weight can be determined in other modes. For example, if the first target display luminance approaches the first display luminance, a greater first weight is determined based on the empirical value. Thus, the Mura morphology of the first target display luminance compensation is more similar to the Mura morphology at the first display luminance. For example, if the voltage distribution manner of the DBV is not uniform, the first weight and the second weight may also be determined according to the distribution relationship of the voltage values. The first weight and the second weight in the application can be adjusted according to actual conditions.

In step S204, the computing device determines a first fusion gray level according to the product of the first target gray level and the first weight and the sum of the products of the second target gray level and the second weight.

For example, the first target gray level is 32 levels, and the first weight isThe second target gray scale is 64 levels, and the second weight isThe first fused gray level is equal to +.>A stage.

In step S205, the computing device determines a first target gamma curve according to each first fusion gray level and the screen brightness corresponding to the first fusion gray level. The first target gamma curve is a gamma curve corresponding to the first target DBV.

For example, the first blended gray level is 40 levels, the corresponding screen brightness is 100nit, the second blended gray level is 64 levels, and the corresponding screen brightness is 120nit.

The first target gamma curve can be obtained by fitting based on the first fusion gray scale and the corresponding screen brightness, and the specific fitting mode of the first target gamma curve can refer to the first gamma curve, which is not described in detail in the embodiment of the present application.

In step S206, the computing device determines a first target gray-scale compensation curve according to the first target gamma curve.

The specific implementation manner of step S206 may refer to step S14, which is not described in detail in the present disclosure.

In step S207, the computing device determines first target gray-scale compensation data according to the first target gray-scale compensation curve.

In step S208, the computing device fuses the first target gray-scale compensation data to the first gray-scale compensation table.

In some embodiments, the computing device generates a fourth gray-scale compensation table from the first target compensation data, and the specific fusion mode of the fourth gray-scale compensation table and the first gray-scale compensation table may refer to the fusion mode of the third gray-scale compensation table to the second gray-scale compensation table, and after the fourth gray-scale compensation table is fused to the first gray-scale compensation table, the fused first gray-scale compensation table may be obtained.

In some embodiments, the computing device obtains a first target compensation coefficient of the first target compensation data, and a compensation coefficient corresponding to the first gray-scale compensation table, generates a first target fusion compensation coefficient based on the two compensation coefficients, and generates a fused first gray-scale compensation table according to the first target fusion compensation coefficient. The specific fusion manner may be referred to the above embodiments, and the disclosure is not repeated herein.

In step S209, the computing device compensates the gray scales under all DBV to the target gray scale according to the fused first gray scale compensation table.

As shown in fig. 19, step S20 includes steps S211 to S219.

In step S211, the computing device acquires a second target DBV of the display screen. The second target DBV includes a DBV in a PWM dimming mode.

In step S212, the DBV computing device determines a first target screen luminance corresponding to each gray level in the first gamma curve and a second target screen luminance corresponding to each gray level in the second gamma curve, respectively.

In the PWM dimming mode, the Mura is irregular, so that the gamma curves corresponding to other DBVs are obtained between the first gamma curve and the second gamma curve in at least one of interpolation, weighting and fitting based on the principle of compensating the same gray scale.

For example, when the gray scale is 16 levels, the first target screen brightness in the first gamma curve is 20nit and the second target screen brightness in the second gamma curve is 15nit.

In step S213, the computing device determines a first weight based on the correspondence between the second target DBV and the first DBV, and determines a second weight based on the correspondence between the second target DBV and the second DBV.

The determining manner of the first weight and the second weight may refer to step S203.

In addition, in the PWM dimming mode, the current of the display screen is unchanged, and the duty ratio affects the brightness, so that gray-scale compensation needs to be performed based on the same gray-scale compensation principle. Thus, at low DBV, a second greater weight may be determined to bias the gray level compensation curve corresponding to the second target DBV more toward the second gray level compensation curve.

The second weight is determined asThe first weight is +.>

In step S214, the computing device determines a first fused screen luminance according to the product of the first target screen luminance and the first weight and the sum of the product of the second target screen luminance and the second weight.

For example, when the first target screen brightness is 20nit, the first weight isWhen the second target screen brightness is 15nit, the second weight is +.>The first blended screen brightness was 16nit.

In step S215, the computing device generates a second target gamma curve according to each gray level and the first fusion screen brightness corresponding to each gray level. The second target gamma curve is a gamma curve corresponding to the second DBV.

In step S216, the computing device determines a second target gray-scale compensation curve according to the second target gamma curve.

The specific implementation manner of step S216 may refer to step S14, which is not described in detail in the present disclosure.

In step S217, the computing device determines second target gray-scale compensation data according to the second target gray-scale compensation curve.

In step S218, the computing device fuses the second target gray-scale compensation data to the first gray-scale compensation table.

The specific way of fusing the second target compensation data to the first gray-scale compensation table may refer to the fusing way of the first target gray-scale compensation data.

In step S218, the computing device compensates the gray scales under all DBV to the target gray scale according to the fused first gray scale compensation table.

The steps S15-S20 can be completed in an equipment factory after the display screen leaves the factory, so that the Demura method refers to the Mura form of other DBVs, and the Mura compensation of the low DBVs can be more accurate.

Wherein the application shows an embodiment of performing step S15-step S17 after step S11-step S14 is implemented. In some embodiments, steps S15 to S17 may be performed simultaneously with steps S11 to S14, and after the first gray-scale compensation data and the second gray-scale compensation data are obtained, the first gray-scale compensation data and the second gray-scale compensation data are fused, which is not limited by the time period and the place where each step is implemented.

The gray level compensation method provided by the embodiment of the application can be used for fusing the gray level compensation data of different DBVs, so that the gray level compensation data of low DBVs are supplemented on the basis of the gray level compensation data of high DBVs in the process of carrying out gray level compensation through hardware, only a single group of gray level compensation tables are generated, the gray level compensation on the hardware is completed, and the performance requirement of the hardware is met. Further, in the process of gray level compensation through software, gray level compensation is performed according to the obtained gray level compensation data under different DBVs under a DC dimming mode and a PWM dimming mode based on different principles, more accurate gray level compensation data of other DBVs can be obtained, different fusion modes are selected for fusion of the data, a group of gray level compensation tables are generated, gray level compensation under all DBVs can be performed on a display screen, and Mura compensation effects under different DBVs are improved.

It will be appreciated that in order to achieve the above-described functionality, a computing device, image acquisition apparatus, etc., includes corresponding hardware structures and/or software modules that perform the respective functions. Those skilled in the art will readily appreciate that the present application can be implemented in hardware or a combination of hardware and computer software, as a gray level compensation method step of each of the examples described in connection with the disclosed embodiments of the application. Whether a function is implemented as hardware or electronic device software driven hardware depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

The application also provides a gray level compensation system, which comprises: an image generating device for displaying a first image with a first DBV including a DBV in a direct current DC dimming mode on a display screen; the image acquisition device is used for shooting the display screen to obtain first image data, and the first image data comprises image data of a first image under at least one group of preset gray scales; the computing equipment is used for analyzing the first image data to obtain first brightness data, wherein the first brightness data comprises the corresponding relation between the gray scale of the first image under the first DBV and the brightness of the screen; the computing device is further used for determining first gray-scale compensation data according to the first brightness data; the image generating device is further used for displaying a second image on the display screen through at least one second DBV, and the second DBV comprises a DBV in a Pulse Width Modulation (PWM) dimming mode; the image acquisition device is also used for shooting the display screen to obtain second image data, and the second image data comprises image data of the second image under at least one group of preset gray scales corresponding to each second DBV; the computing equipment is also used for analyzing the second image data to obtain second brightness data, wherein the second brightness data comprises the corresponding relation between the gray scale of the second image under each second DBV and the brightness of the screen; the computing device is further used for determining second gray-scale compensation data according to the second brightness data; the computing device is further used for generating a first gray-scale compensation table according to the first gray-scale compensation data and the second gray-scale compensation data; the computing device is further used for compensating the gray scales under all DBVs to target gray scales according to the first gray scale compensation table.

The embodiment of the application also provides a chip system which comprises at least one processor and at least one interface circuit. The processors and interface circuits may be interconnected by wires. For example, the interface circuit may be used to receive signals from other devices (e.g., a memory of an electronic apparatus). For another example, the interface circuit may be used to send signals to other devices. The interface circuit may, for example, read instructions stored in the memory and send the instructions to the processor. The instructions, when executed by a processor, may cause a computing device to perform the various steps of the embodiments described above. Of course, the system-on-chip may also include other discrete devices, which are not particularly limited in accordance with embodiments of the present application.

Embodiments of the present application also provide a computer-readable storage medium comprising computer instructions which, when run on a computing device as described above, cause the computing device to perform the functions or steps performed in the method embodiments described above.

Embodiments of the present application also provide a computer program product which, when run on a computer, causes the computer to perform the functions or steps performed in the method embodiments described above.

It will be apparent to those skilled in the art from this description that, for convenience and brevity of description, only the above-described division of the functional modules is illustrated, and in practical application, the above-described functional allocation may be performed by different functional modules according to needs, i.e. the internal structure of the apparatus is divided into different functional modules to perform all or part of the functions described above.

In the several embodiments provided by the present application, it should be understood that the disclosed apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are merely illustrative, e.g., the division of the modules or units is merely a logical functional division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another apparatus, or some features may be omitted, or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices or units, which may be in electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and the parts displayed as units may be one physical unit or a plurality of physical units, may be located in one place, or may be distributed in a plurality of different places. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in the embodiments of the present application may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.

The integrated units, if implemented in the form of software functional units and sold or used as stand-alone products, may be stored in a readable storage medium. Based on such understanding, the technical solution of the embodiments of the present application may be essentially or a part contributing to the prior art or all or part of the technical solution may be embodied in the form of a software product stored in a storage medium, including several instructions for causing a device (may be a single-chip microcomputer, a chip or the like) or a processor (processor) to perform all or part of the steps of the method described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read Only Memory (ROM), a random access memory (random access memory, RAM), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

The foregoing is merely illustrative of specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions within the technical scope of the present application should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A gray scale compensation method, comprising:

the display screen displays a first image with a first display brightness, wherein the first display brightness comprises display brightness in a Direct Current (DC) dimming mode;

the image acquisition device shoots the display screen to obtain first image data, wherein the first image data comprises image data of the first image under at least one group of preset gray scales;

the computing equipment analyzes the first image data to obtain first brightness data, wherein the first brightness data comprises the corresponding relation between gray scale of the first image under the first display brightness and screen brightness;

the computing device determines first gray-scale compensation data according to the first brightness data;

the display screen displays a second image with at least one second display brightness, wherein the second display brightness comprises display brightness in a Pulse Width Modulation (PWM) dimming mode;

The image acquisition device shoots the display screen to obtain second image data, wherein the second image data comprises at least one group of image data of the second image under the preset gray scale corresponding to each second display brightness;

the computing equipment analyzes the second image data to obtain second brightness data, wherein the second brightness data comprises the corresponding relation between the gray scale of the second image under each second display brightness and the screen brightness;

the computing device determines second gray-scale compensation data according to the second brightness data;

the computing device generates a first gray scale compensation table according to the first gray scale compensation data and the second gray scale compensation data;

the computing device compensates the gray scale under all display brightness to the target gray scale according to the first gray scale compensation table.

2. The gray scale compensation method of claim 1, wherein the first luminance data comprises a first gamma curve, and wherein the first gray scale compensation data comprises a first gray scale compensation curve; the computing device determining first gray-scale compensation data from the first luminance data, comprising:

the computing equipment derives the first gray level compensation curve according to the first gamma curve and a preset standard gamma curve, the first gray level compensation curve comprises a corresponding relation between each gray level and a first compensation gray level, and the first compensation gray level is used for compensating the corresponding gray level to a target gray level.

3. The gray scale compensation method of claim 2 wherein the computing device determining first gray scale compensation data from the first luminance data comprises:

the computing equipment carries out polynomial fitting on the preset gray scale in a first gray scale interval and the corresponding first compensation gray scale to obtain a first part of the first gray scale compensation curve, wherein the first gray scale interval is larger than a first gray scale threshold value;

the computing equipment performs curve fitting on at least two preset gray scales and the corresponding first compensation gray scales in a second gray scale interval based on a display lookup table LUT to obtain a second part of the first gray scale compensation curve, wherein the second gray scale interval is smaller than or equal to the first gray scale threshold value and larger than or equal to a second gray scale threshold value;

the computing equipment maps gray scales in a third gray scale interval according to the second part of the first gray scale compensation curve to obtain a third part of the first gray scale compensation curve, wherein the third gray scale interval is smaller than the second gray scale threshold;

the computing device generates the first gray-scale compensation curve from a first portion of the first gray-scale compensation curve, a second portion of the first gray-scale compensation curve, and a third portion of the first gray-scale compensation curve.

4. The gray scale compensation method of claim 3 wherein after determining first gray scale compensation data from said first luminance data, said computing device further comprises:

the computing equipment generates a group of second gray scale compensation tables according to the first gray scale compensation data, each gray scale corresponds to one second gray scale compensation table, and the second gray scale compensation table comprises the first compensation gray scale corresponding to each gray scale under the first display brightness;

the computing device burns the second gray-scale compensation table to a storage device.

5. The gray scale compensation method of claim 4, wherein the second luminance data comprises a second gamma curve, and wherein the second gray scale compensation curve comprises a second gray scale compensation curve; the computing device determining second gray scale compensation data from the second luminance data, comprising:

the computing equipment derives a second gray level compensation curve according to the second gamma curve and a preset standard gamma curve, the second gray level compensation curve comprises a corresponding relation between each gray level and a second compensation gray level, and the second compensation gray level is used for compensating the corresponding gray level to the target gray level.

6. The gray scale compensation method of claim 5 wherein said computing device determining second gray scale compensation data from said second luminance data comprises:

the computing equipment carries out polynomial fitting on the preset gray scale in a fourth gray scale interval and the corresponding second compensation gray scale to obtain a first part of the second gray scale compensation curve, wherein the fourth gray scale interval is larger than a first gray scale threshold value;

the computing equipment performs curve fitting on at least two preset gray scales and the corresponding second compensation gray scales in a fifth gray scale interval based on a display lookup table LUT to obtain a second part of the second gray scale compensation curve, wherein the fifth gray scale interval is smaller than or equal to the first gray scale threshold value and larger than or equal to a second gray scale threshold value;

the computing equipment maps gray scales in a sixth gray scale interval according to the second part of the second gray scale compensation curve to obtain a third part of the second gray scale compensation curve, wherein the sixth gray scale interval is smaller than the second gray scale threshold value;

the computing device generates the second gray-scale compensation curve from the first portion of the second gray-scale compensation curve, the second portion of the second gray-scale compensation curve, and the third portion of the second gray-scale compensation curve.

7. The gray scale compensation method of claim 6, wherein the computing device generates a first gray scale compensation table from the first gray scale compensation data and the second gray scale compensation data, comprising:

the computing device generates a group of third gray scale compensation tables according to the second gray scale compensation data, each gray scale corresponds to one third gray scale compensation table, and the third gray scale compensation table comprises the second compensation gray scale corresponding to each gray scale under the second display brightness.

8. The gray scale compensation method of claim 7, wherein the computing device generates a first gray scale compensation table from the first gray scale compensation data and the second gray scale compensation data, comprising:

the computing device reads the second gray-scale compensation table from the storage device;

the computing device fuses the third gray-scale compensation table to the second gray-scale compensation table to generate the first gray-scale compensation table, and the fusing comprises weighting, fitting and/or linearly interpolating the first compensation gray-scale and the second compensation gray-scale corresponding to each gray-scale.

9. The gray scale compensation method of claim 6, wherein the computing device generates a first gray scale compensation table from the first gray scale compensation data and the second gray scale compensation data, comprising:

the computing equipment analyzes the second gray-scale compensation table to obtain the first gray-scale compensation curve;

the computing equipment acquires a first gray-scale compensation coefficient corresponding to the first gray-scale compensation curve, wherein the first gray-scale compensation coefficient comprises a polynomial coefficient of a curve equation corresponding to the first gray-scale compensation curve;

the computing equipment analyzes the second gray-scale compensation data to obtain a second gray-scale compensation curve;

the computing equipment acquires a second gray-scale compensation coefficient corresponding to the second gray-scale compensation curve, wherein the second gray-scale compensation coefficient comprises a polynomial coefficient of a curve equation corresponding to the second gray-scale compensation curve;

the computing device fuses the first gray-scale compensation coefficient and the second gray-scale compensation coefficient to obtain a third gray-scale compensation coefficient, and the fusing comprises weighting and/or linearly interpolating the first gray-scale compensation coefficient and the second gray-scale compensation coefficient;

the computing equipment determines a third gray-scale compensation curve corresponding to the third gray-scale compensation coefficient as third gray-scale compensation data;

The computing device generates the first gray scale compensation table from the third gray scale compensation data.

10. The gray scale compensation method according to claim 8 or 9, wherein the computing device compensates gray scales at all display brightness to a target gray scale according to the first gray scale compensation table, comprising:

the computing device obtains a first target display brightness of the display screen, the first target display brightness comprising display brightness in a DC dimming mode;

the computing device determines a first target gray level corresponding to each screen brightness in the first gamma curve and a second target gray level corresponding to each screen brightness in the second gamma curve;

the computing device determines a first weight based on a correspondence of the first target display brightness and the first display brightness, and determines a second weight based on a correspondence of the first target display brightness and the second display brightness;

the computing device determines a first fused gray scale according to the product of the first target gray scale and the first weight and the sum of the product of the second target gray scale and the second weight;

the computing equipment determines a first target gamma curve according to each first fusion gray level and the screen brightness corresponding to the first fusion gray level, wherein the first target gamma curve is a gamma curve corresponding to the first target display brightness;

The computing equipment determines a first target gray-scale compensation curve according to the first target gamma curve;

the computing equipment determines first target gray-scale compensation data according to the first target gray-scale compensation curve;

the computing device fuses the first target gray-scale compensation data to the first gray-scale compensation table;

and the computing equipment compensates the gray scale under all display brightness to the target gray scale according to the fused first gray scale compensation table.

11. The gray scale compensation method according to claim 8 or 9, wherein the computing device compensates gray scales at all display brightness to a target gray scale according to the first gray scale compensation table, comprising:

the computing device obtains second target display brightness of the display screen, wherein the second target display brightness comprises display brightness in a PWM dimming mode;

the computing device determines the first target screen brightness corresponding to each gray scale in the first gamma curve and the second target screen brightness corresponding to each gray scale in the second gamma curve;

the computing device determines a first weight based on a correspondence of the second target display brightness and the first display brightness, and determines a second weight based on a correspondence of the second target display brightness and the second display brightness;

The computing device determining a first fused screen brightness from a sum of a product of the first target screen brightness and the first weight and a product of the second target screen brightness and the second weight;

the computing equipment generates a second target gamma curve according to each gray level and the first fusion screen brightness corresponding to each gray level, wherein the second target gamma curve is a gamma curve corresponding to the second target display brightness;

the computing equipment determines a second target gray-scale compensation curve according to the second target gamma curve;

the computing device determines second target gray-scale compensation data from the second target gray-scale compensation curve;

the computing device fuses the second target gray-scale compensation data to the first gray-scale compensation table;

12. A gray scale compensation system, comprising:

the image generation device is used for displaying a first image by the display screen at a first display brightness, wherein the first display brightness comprises display brightness in a Direct Current (DC) dimming mode;

The image acquisition device is used for shooting the display screen to obtain first image data, wherein the first image data comprises image data of the first image under at least one group of preset gray scales;

the computing equipment is used for analyzing the first image data to obtain first brightness data, wherein the first brightness data comprises the corresponding relation between the gray scale of the first image under the first display brightness and the screen brightness;

the computing device is further configured to determine first gray-scale compensation data according to the first luminance data;

the image generating device is further configured to display a second image on the display screen with at least one second display brightness, where the second display brightness includes a display brightness in a PWM dimming mode;

the image acquisition device is further used for shooting the display screen to obtain second image data, and the second image data comprise at least one group of image data of the second image under the preset gray scale corresponding to each second display brightness;

the computing device is further configured to parse the second image data to obtain second luminance data, where the second luminance data includes a corresponding relationship between a gray scale of the second image at each second display luminance and a screen luminance;

The computing device is further configured to determine second gray-scale compensation data according to the second luminance data;

the computing device is further configured to generate a first gray-scale compensation table according to the first gray-scale compensation data and the second gray-scale compensation data;

the computing device is further configured to compensate gray scales under all display brightness to a target gray scale according to the first gray scale compensation table.