Screen uniformity correction method based on LED module optical parameter difference

Abstract

The present application relates to a kind of screen uniformity correction method based on the difference of LED module optical parameter, the method is carried out LED screen shooting under different gray levels using acquisition equipment, obtain gray scale sequence;From each gray scale, the luminance value of each module is extracted and the gray scale-luminance variation curve of each module is fitted;For any module, the gray scale corresponding to the target value in the gray scale-luminance variation curve is obtained, and further the ink color correction ratio of the module is obtained, the luminance value of all pixel points in the module under the highest gray level is multiplied by the ink color correction ratio, to obtain the corrected luminance value of each pixel point under the highest gray level;The point-by-point correction coefficient matrix C of whole screen is calculated using the corrected luminance value of each pixel point;Whole screen point-by-point correction coefficient matrix C is uploaded to LED screen hardware control system, that is, the whole screen correction is completed.The present application eliminates the phenomenon of inconsistent luminance after correction caused by ink color, and improves the whole screen correction effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optoelectronics and information display technology, and relates to a pixel-level screen uniformity collection correction method for optical parameter difference of an LED module. BACKGROUND

[0002] With the development of new ultra-high density LED flat panel display technology, LED will become the preferred technology for future super large high-definition television display screens, has the advantages of wide color gamut, high luminous efficiency, fast response speed, wide working temperature range, etc., and is widely used in high-end display, flat panel display backlight and lighting fields, especially in the fields of cinema and medical teaching, and has important market prospects.

[0003] An important indicator of the quality of large LED display products is screen uniformity, mainly reflected in three aspects of brightness, chrominance and directional characteristics. The description of directionality is generally listed as an index of viewing range. For display products, the uniformity of brightness and chrominance is more concerned by observers. The raw material of LED display products is LED dies, which are semiconductor devices. Due to their own reasons, they have discreteness in brightness. In addition, the brightness of LED dies will decay after being used for a certain period of time, and the decay degree of each primary color is different, which will cause the display of a display screen with good uniformity to be uneven after working for a period of time.

[0004] The main reasons for the screen non-uniformity defects are as follows:

[0005] (a) Each primary color LED light-emitting tube has great discreteness in brightness. LED flat panel display screens are composed of thousands of LED light-emitting tubes with relatively large differences in brightness. Usually, even LED light-emitting tubes of the same brightness level have a 30% deviation in brightness, which is the most fundamental reason for the "pitting" and "mosaic" defects of LED flat panel displays.

[0006] (b) The chrominance coordinates of LED light-emitting tubes are distributed discretely. Usually, the dominant wavelengths of LED light-emitting tubes of the same level differ by within 5nm. However, even LED light-emitting tubes of the same wavelength level have a non-negligible color difference in reproducible color due to different spectral power distributions of their light emission.

[0007] (c) LED light-emitting tubes have different decay degrees over time. LED light-emitting tubes that are originally uniform in brightness will become non-uniform after being used for a period of time.

[0008] (d) Other factors, such as inconsistency of driving circuits, influence of environmental temperature, defects in circuit design, errors in structure processing, etc., can also cause non-uniformity.

[0009] With the development of display technology and the improvement of people's entertainment level, the brightness uniformity problem of LED display becomes a prominent problem affecting display quality, and becomes a focal point problem to be solved at present.

[0010] At present, the method to completely solve the uniformity problem of LED screen is to adopt brightness and color compensation technology, to realize the independent adjustment of the brightness and color of each light emitting primary color, to eliminate the brightness and color deviation during display, and to ensure the uniformity and consistency of the color and brightness of the whole screen. Through the adoption of full-screen "point-by-point" uniformization correction technology, the display quality is improved in quality. In the white field, the "mosaic" and "pitting" phenomenon of the display screen is eliminated, and high uniformity display effect is achieved.

[0011] One of the keys to solve this problem is first how to collect the three primary color brightness and chroma information of millions of pixels on the LED flat panel display screen back. With the rapid development of modern optical technology and image processing technology, this problem provides an opportunity for research. Suitable optical acquisition equipment can make the light color information of a large number of pixels on the LED flat panel display screen saved in an image, and the test can record the brightness and chroma information of a large number of even the whole screen pixels on the display device within a few seconds.

[0012] Another key problem is to design a suitable correction algorithm. From the obtained relative brightness information of the whole LED screen, a weight lookup table of each primary color of each LED flat panel display pixel is established. When each LED flat panel display pixel on the screen reproduces a certain color, the corresponding weight provided by the lookup table is multiplied first, so as to achieve the purpose of correction. Thus, all the pixels on the screen reproduce the same color when the same data is input, and the purpose of uniformization is achieved.

[0013] However, in the above uniformization process, a new technical challenge is encountered, that is, the different ink colors of the modules affect the light emission of the pixels inside the same module to a certain extent. When the ink color of the module is deep, the module also presents a relatively dark state after lighting. At this time, the camera is used for collection and correction, and the calculated coefficient is uploaded. The brightness of the module with deep ink color is still relatively dark, which affects the consistency after correction. SUMMARY

[0014] The technical problem to be solved by the present application is to provide a screen uniformity correction method based on the optical parameter difference of LED modules, which can eliminate the phenomenon of inconsistent brightness after correction caused by the difference in ink color of the modules, and improve the whole screen correction effect.

[0015] To solve the above technical problems, the screen uniformity correction method based on the optical parameter difference of the LED module of the present application is as follows: full-screen point-by-point correction is carried out at the highest gray level of the LED screen to obtain the luminance values of all pixel points; the target value is set to be 75%-85% of the average value of the luminance of all pixel points; the LED screen is photographed at different gray levels by using a collection device to obtain a sequence of gray scale images; the luminance value of each module is extracted from each gray scale image and the gray scale-luminance change curve of each module is fitted; for any module, the gray level Gt corresponding to the target value in the gray scale-luminance change curve is obtained, Gt / 2 n , and the ink color correction ratio of the module is Gt / 2

[0016] The luminance value of each module is the sum of the luminance values of all pixel points in the module on the gray scale image.

[0017] The gray scale-luminance change curve of each module is fitted by using a binary first-order equation y=ax 2 +bx+c; y represents the luminance value of the module, x represents the gray level, and a, b, and c are coefficients.

[0018] Further, full-screen point-by-point correction is carried out at the highest gray level when the LED screen displays red, green, and blue three primary colors respectively to obtain the luminance values of all pixel points when displaying red, green, and blue.

[0019] Further, the target values corresponding to the red, green, and blue three primary colors are respectively determined according to the luminance values of all pixel points when displaying red, green, and blue.

[0020] Further, the LED screen is photographed when displaying red, green, and blue three primary colors respectively at different gray levels by using a collection device to obtain a sequence of red gray scale images, a sequence of green gray scale images, and a sequence of blue gray scale images.

[0021] The luminance value of each module is extracted from each gray scale image of the sequence of red gray scale images, the sequence of green gray scale images, and the sequence of blue gray scale images and the gray scale-luminance change curve of each module corresponding to the red, green, and blue three primary colors is fitted; for any module, the gray levels GRt, GGt, and GBt corresponding to the target values of the red, green, and blue three primary colors are respectively obtained, GRt / 2 n , GGt / 2 n , and GBt / 2 n , which are the ink color correction ratios of the module corresponding to the red, green, and blue three primary colors.

[0022] Beneficial effect: in the past, the collection is carried out at a gray level, and it is generally considered that the brightness of the chip and the gray level change linearly. The correction coefficient obtained by collecting at a gray level is applicable to all gray levels. However, due to the influence of packaging process and ink color, the change is not linear, but often curved. And it presents an aggregation performance in the unit of module ink color. According to the characteristics of the module ink color, the brightness values of all modules at a few gray levels are quickly and accurately obtained by using the camera, and the gray-brightness change curve of each module is fitted. Then the ink color correction ratio is obtained, and the collected lamp point brightness is corrected again, which eliminates the inconsistency of the corrected brightness caused by the ink color and improves the whole screen correction effect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The flowchart of the present application.

[0024] Figure 2 The picture of the module ink color difference of the LED screen shot by the camera without power.

[0025] Figure 3a , Figure 3b The gray-brightness change curve of different ink color modules when the control system accuracy is 13bit (the gray value changes from 0 to 8191). DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in combination with the drawings and examples. It can be understood that the specific examples described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0027] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For ordinary skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature "under", "below" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0029] In the description of the present embodiment, the terms "on", "under", "left", "right" and the like orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only used to distinguish in the description and have no special meaning.

[0030] As shown in Figure 1 The LED module-based screen uniformity correction method of the present application specifically as follows:

[0031] (1) Set the gamma value of the LED screen control system to 1, and perform full-screen point-by-point correction at the highest gray level. Full-screen point-by-point correction is a commonly used technical means in the industry, which will not be described here. The brightness values of all pixel points of the full screen at the highest gray level are obtained during the correction process. In the point-by-point correction link, the target values required for calculating the red, green and blue three-primary color correction coefficient matrix are LRt, LGt and LBt, respectively. The target values are generally 75%-85% of the average brightness of the full-screen pixel points at the highest gray level. Here, only the red, green and blue brightness values of each pixel point and the target values are needed, and the point-by-point correction coefficient matrix does not need to be calculated.

[0032] (2) Use the acquisition device to take pictures of the LED screen displaying different gray levels of red, green and blue three-primary colors, respectively, to obtain a red gray scale sequence Pr1-Prm, a green gray scale sequence Pg1-Pgm and a blue gray scale sequence Pb1-Pbm; wherein m represents the number of gray levels output by the control system, generally 5-11. All pictures in the gray scale sequence are taken under the same aperture and focal length conditions of the camera, and each pixel point on the LED screen is in a lit state during shooting.

[0033] (3) Extract the luminance value corresponding to each module of the LED screen on each picture of the photographed red, green, and blue grayscale image sequences. The luminance value corresponding to each module is represented by the sum of the luminance values of all the pixel points inside the module on the picture. Denoted as Lji. i represents the shooting grayscale level, and j represents the module label, which is determined by the screen resolution and module specifications. Since each primary color grayscale image sequence contains m grayscale level pictures, m luminance values corresponding to each module can be obtained; let the luminance value corresponding to the i-th grayscale level Gi of each module be Li, and the grayscale-luminance variation curve of each module can be fitted. The grayscale-luminance variation curve is hereinafter referred to as GL curve, as shown in FIG. 1. Figure 3a 、 Figure 3b The x-axis coordinate in the GL curve represents the grayscale level, denoted as G, and the variation interval is 0-255. n Here, n is the control system accuracy (i.e., the bit number of grayscale data in the control system, generally 13-16). The y-axis coordinate represents the module luminance value, denoted as L. Here, the red, green, and blue luminance values of the module need to be collected, and one GL curve for each of the red, green, and blue colors of each module is fitted.

[0034] The curve fitting uses a binary linear equation, represented as y = ax 2 + bx + c. The coefficients a, b, and c are obtained according to multiple sets of input parameters x (grayscale level) and y (module luminance value). In this way, the fitted luminance under different input grayscale levels for each module can be obtained.

[0035] (4) According to the red, green, and blue target values used in the correction process, for any module, the grayscale levels corresponding to the red, green, and blue target values GRt, GGt, and GBt are obtained, respectively, and GRt / 2 n , GGt / 2 n , and GBt / 2 n are the ink color correction ratios of the red, green, and blue colors of the module, respectively. The ink color correction ratio is multiplied by the luminance value of each pixel point at the highest grayscale level to obtain the corrected luminance value of each pixel point, and then the final point-by-point correction coefficient matrix C is calculated using the corrected luminance value of each pixel point. The display screen correction coefficient matrix calculated by the point-by-point luminance value belongs to a commonly used technical means in the industry, which will not be described here.

[0036] (4) Upload the whole-screen point-by-point correction coefficient matrix C to the hardware control system, and the whole-screen correction is completed.

[0037] Example 1:

[0038] The resolution is 1920*1080, the point spacing is P0.9mm, and the module specifications are 160*120. The whole screen uses (1920 / 160)*(1080 / 120) = 12*9 = 108 modules. The correction method is as follows:

[0039] (1) Control system precision is 13 bit, control system gamma value is set to 1, and full-screen point-by-point correction is performed at the highest (software end is 255, hardware control system end is 8191) gray level. The full-screen point-by-point correction belongs to the commonly used technical means in the industry, which will not be described here. The brightness value of all pixel points in the full screen at the current gray level is obtained in the correction process. In the point-by-point correction link, the target value Lt is needed when calculating the red, green and blue three primary color correction coefficient matrix. The target value of the three primary colors is represented as LRt, LGt and LBt respectively. The selection of the target value is 80% of the average brightness value of the full-screen pixel points.

[0040]

[0041]

[0042] grayR, grayG, grayB are the red, green and blue brightness values of the pixel points obtained by the camera in the correction link. Here, only the red, green and blue brightness and the target value of each pixel point need to be obtained, without calculating the point-by-point correction coefficient matrix.

[0043] (2) Use the acquisition device to capture the red, green and blue three primary colors displayed on the full screen at the hardware output control end gray level = 2000, 3000, 4000, 5000, 6000, 7000, 8000, a total of 7 gray levels. The obtained red gray scale sequence is represented as Pr1-Pr7, the obtained green gray scale sequence is represented as Pg1-Pg7, and the obtained blue gray scale sequence is represented as Pb1-Pb7 (7 represents the number of gray levels output by the control system, here 7 gray levels are selected for shooting). All pictures in the gray scale sequence cannot be saturated, and are shot under the same aperture and focal length conditions. Each pixel point on the LED screen is in a lighted state.

[0044] (3) Extract the brightness value of each module on the screen from the obtained gray scale sequence. The module brightness value is represented by the sum of the brightness values of all pixel points inside the module in the captured picture. Denoted as Lji. i represents the captured gray level, and j represents the module label, which is determined by the screen resolution and module specification (1≤j≤108). Seven gray levels are captured, and seven brightness values of each module for each primary color are obtained. From the gray level Gi of each module and the brightness value Li at the gray level, the gray-brightness variation curve of each module is fitted. The gray-brightness variation curve is hereinafter referred to as GL curve, as shown in Figure 3a Figure 3b The x-axis coordinate in the curve represents the gray value used for collection, represented by G, and the variation interval is 0-2 n . Here n = 13. The y-axis coordinate represents the module brightness value, represented by L. Here, the brightness values of the red, green and blue three primary colors displayed by the module need to be collected, and one GL curve is fitted for each module for red, green and blue.​

[0045] Curve fitting uses a binary linear equation. Represented as y=ax 2 +bx+c. According to each module 7 group input parameters x and y to obtain the coefficient parameters a, b, c. So you can get each module different input gray level under the fitting brightness value.

[0046] (4) According to the target value Lt used in the correction process, the Gt value corresponding to the target value Lt in each module GL curve is obtained, Gt / 2 13 That is the module ink color correction ratio. All pixel points in each module use the same ink color correction ratio. Ink color correction ratio multiplied by the brightness value of each pixel point under the highest gray level, get each pixel point of the correction brightness value, through the point by point brightness value calculation display screen correction coefficient matrix belongs to the commonly used technical means in the industry, here no longer tedious. Get the final point by point correction coefficient matrix C.

[0047] (5) upload C to the hardware control system, that is, complete the whole screen correction.

[0048] Example 2:

[0049] Resolution is 1920*1080, point spacing is P1.27mm display screen, module specification 120*90. The whole screen uses (1920 / 120)*(1080 / 90)=16*12=192 modules. Its correction method is as follows:

[0050] (1) control system precision is 14bit, control system gamma value is set to 1, at the highest (software side is 255, hardware control system side 16383) gray level, carry out full screen point by point correction. Full screen point by point correction belongs to the commonly used technical means in the industry, here no longer tedious. In the correction process, the brightness value of all pixel points in the current gray level will be obtained. In the point by point correction link, the target value Lt is needed when calculating the red, green and blue correction coefficient matrix. Here the target value of three primary colors is represented as LRt, LGt and LBt. The selection of target value is 75% of the average value of full screen pixel gray.

[0051]

[0052] grayR, grayG, grayB are the red, green and blue brightness values of the pixel points obtained by the camera in the correction process. Here we only need to obtain the red, green and blue brightness values of each pixel point and the target value, without calculating the point by point correction coefficient matrix.

[0053] (2) Use the acquisition device to take pictures when the hardware output control terminal displays red, green and blue three primary colors in full screen at 5 gray levels, i.e. 1024, 4096, 8192, 14352 and 16383. The obtained red gray scale sequence is denoted as Pr1-Pr5, the obtained green gray scale sequence is denoted as Pg1-Pg5, and the obtained blue gray scale sequence is denoted as Pb1-Pb5 (5 represents the number of gray levels of the control system output, and 5 gray levels are selected for taking pictures here). All pictures in the gray scale sequence cannot be saturated, and each pixel point on the LED screen is in a lighted state under the same aperture and focal length conditions.

[0054] (3) Extract the brightness value of each module on the screen from the obtained gray scale sequence. The module brightness value is represented by the sum of the brightness values of all pixel points inside the module on the taken picture. Denoted as Lji. i represents the taken gray level, and j represents the module label, which is determined by the screen resolution and module specification (1≤j≤192). Five gray values of each module for each primary color are obtained by taking 5 gray levels. The gray level Gi of each module and the brightness L at the gray level are used to fit the gray-brightness variation curve of each module. The gray-brightness variation curve is referred to as GL curve here, as shown in Figure 3a 、 3b The x-axis coordinate in the curve represents the gray level used for collection, denoted as G, and the variation interval is 0-214. n Here, n=14. The y-axis coordinate represents the module brightness value, denoted as L. Here, the brightness value of the module when displaying red, green and blue three primary colors needs to be collected, and one GL curve for each module is fitted for red, green and blue respectively.

[0055] The curve fitting adopts a binary linear equation, denoted as y=ax 2 +bx+c. The coefficient parameters a, b and c are obtained according to 5 sets of input parameters x and y of each module. Thus, the fitting brightness of each module at different input gray levels can be obtained.

[0056] (4) According to the target value Lt used in the correction process, the Gt value corresponding to the target value Lt in the GL curve of each module is obtained, and Gt / 2 14 is the module ink color correction ratio. The same ink color correction ratio is used for all pixel points in each module. The ink color correction ratio is multiplied by the brightness value of each pixel point at the highest gray level in step (1) to obtain the corrected brightness value of each pixel point. The display screen correction coefficient matrix is calculated by point-by-point brightness value calculation, which belongs to the commonly used technical means in the industry, and will not be described here. The final point-by-point correction coefficient matrix C is obtained.

[0057] (5) Upload C to the hardware control system, and the whole screen correction is completed.

Claims

1. A method for screen uniformity correction based on LED module optical parameter difference, characterized in that The method is as follows: full-screen point-by-point correction is carried out at the highest gray level of the LED screen to obtain the luminance values of all pixel points; the target value is set as 75%-85% of the average value of the luminance of all pixel points; the LED screen is shot at different gray levels by using a collecting device to obtain a gray scale sequence; the luminance values of each module are extracted from each gray scale to fit a gray scale-luminance change curve of each module; for any module, the gray level Gt corresponding to the target value in the gray scale-luminance change curve is obtained, Gt / 2 n is the ink color correction ratio of the module, the ink color correction ratio is multiplied by the luminance values of all pixel points in the module at the highest gray level to obtain the corrected luminance values of each pixel point at the highest gray level; the whole-screen point-by-point correction coefficient matrix C is calculated by using the corrected luminance values of each pixel point; the whole-screen point-by-point correction coefficient matrix C is uploaded to the hardware control system of the LED screen, and the whole-screen correction is completed.

2. The method of claim 1, wherein the method is a method of correcting screen uniformity based on a difference in optical parameters of the LED modules. The brightness value of each module is the sum of the brightness values of all pixel points in the module on the gray scale diagram. 3.The method of claim 1, wherein the optical parameter difference of the LED module is determined by a difference between a first optical parameter of a first LED module and a second optical parameter of a second LED module. The gray-scale-brightness change curve of each module is fitted by a binary first-order equation y = ax 2 + bx + c; y represents the module brightness value, x represents the gray scale, and a, b, and c are coefficients. 4.The method of claim 1, wherein the optical parameter difference of the LED module is determined by a difference between a first optical parameter of a first LED module and a second optical parameter of a second LED module. At the highest gray level, the LED screen displays red, green and blue respectively, and the full-screen point-by-point correction is performed to obtain the brightness values of all pixel points when displaying red, green and blue.

5. The method of claim 4, wherein the optical parameter difference of the LED-based module is a difference in color temperature. The target values corresponding to the red, green and blue three primary colors are determined according to the brightness values of all pixel points when displaying red, green and blue. 6.The method of claim 5, wherein the optical parameter difference of the LED module is determined by a difference between a first optical parameter of a first LED module and a second optical parameter of a second LED module. The LED screen is photographed at different gray levels to obtain a red gray scale sequence, a green gray scale sequence and a blue gray scale sequence.

7. The method of claim 6, wherein the optical parameter difference of the LED module-based screen uniformity correction method is characterized by: The luminance value of each module is extracted from each gray scale of the red gray scale sequence, the green gray scale sequence and the blue gray scale sequence, and a gray scale-luminance change curve corresponding to the red, green and blue three primary colors is fitted for each module; for any module, the gray scale GRt, GGt and GBt corresponding to the target value of the red, green and blue three primary colors are respectively obtained, and GRt / 2 n , GGt / 2 n , GBt / 2 n are the ink color correction proportions of the module corresponding to the red, green and blue three primary colors.

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