Screen gamut correction method

Abstract

Disclosed is a screen color gamut correction method, comprising: obtaining screen color gamut initial values of a plurality of pixel points; converting the screen color gamut initial value of each pixel point to a CIE color gamut to obtain CIE initial coordinate values and converting a target color gamut value of each pixel point to the CIE color gamut to obtain CIE target coordinate values; when the color difference between the CIE initial coordinate values and the CIE target coordinate values exceeds a preset range, iteratively correcting the CIE initial coordinate values; when the color difference between the corrected CIE coordinate values and the CIE target coordinate values meets the preset range, transmitting the corrected CIE coordinate values to the CIE initial coordinate values of the next pixel point. The screen color gamut correction method provided in the application improves the consistency of brightness and color in the screen production process through the method of single-point iterative calculation of target values and value transmission acceleration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of display screen color gamut processing, in particular to a screen color gamut correction method. BACKGROUND

[0002] In the display industry, due to the difference in manufacturing process, color gamut coverage range and other factors, the production consistency is poor, and it is usually necessary to correct the color gamut of the screen. LUT is the full name of Look-Up-Table, that is, lookup table. It is essentially a random access memory, and a signal is input as an address for lookup table, and the content corresponding to the address is found as output. In the display, the pixel value of the original color gamut can be converted into the pixel value of the specified color gamut by using the lookup table, so as to complete the color conversion work. The 3D-LUT can map the color values of the RGB three channels, and describe the accurate behavior of all color points in the three-dimensional color space. It is a high-efficiency color mapping method, and can be used for color gamut calibration of various displays.

[0003] In order to calculate the lookup table, the prior art divides the screen color space into small color spaces according to the measurement points. In the smaller color space, the conversion matrix between the screen color gamut and the target color gamut is calculated by measuring the RGBW color coordinates of the screen. Then, in the continuous iteration, the lookup table that meets the error range is obtained. However, more accurate lookup table usually depends on more measurement points, but the measurement points divide the entire color gamut into more fine color gamut spaces and perform iteration at the same time, which makes the iteration time longer, the accuracy lower and even causes the non-convergence. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a screen color gamut correction method, which improves the consistency of brightness and color in the screen production process by a method of single-point iteration calculation of target value and coordinate value transmission.

[0005] According to an aspect of the present application, a screen color gamut correction method is provided, comprising: obtaining screen color gamut initial values of a plurality of pixel points; converting the screen color gamut initial value of each pixel point to CIE color gamut to obtain CIE initial coordinate values and converting the target color gamut value of each pixel point to CIE color gamut to obtain CIE target coordinate values; when the color difference between the CIE initial coordinate values and the CIE target coordinate values exceeds a preset range, iteratively correcting the CIE initial coordinate values; when the color difference between the corrected CIE coordinate values and the CIE target coordinate values meets the preset range, transmitting the corrected CIE coordinate values to the CIE initial coordinate values of the next pixel point.

[0006] Optionally, the step of iteratively correcting the CIE initial coordinate value comprises: calculating the difference between the CIE initial coordinate value and the CIE target coordinate value on three coordinate axes, determining the iterative correction direction; determining the iterative coefficient on the same coordinate axis according to the signs of the two adjacent difference values on the same coordinate axis; and correcting the CIE initial coordinate value according to the iterative direction and the iterative coefficient.

[0007] Optionally, the method further comprises: judging whether the color difference between the corrected CIE coordinate value and the CIE target coordinate value meets the preset range; and if not, continuing to iteratively correct the CIE coordinate value.

[0008] Optionally, the difference value is the difference between the CIE target coordinate value and the CIE initial coordinate value or the corrected CIE coordinate value on the same coordinate axis.

[0009] Optionally, when any difference value is greater than 0, the iterative correction is performed in the direction of increasing the coordinate value corresponding to the difference value; when any difference value is less than 0, the iterative correction is performed in the direction of decreasing the coordinate value corresponding to the difference value; and when any difference value is equal to 0, the iterative correction of the coordinate value corresponding to the difference value is stopped.

[0010] Optionally, on the same coordinate axis, if the two adjacent difference values are of the same sign, a value greater than 1 is used as the iterative coefficient; and if the two adjacent difference values are not of the same sign, a value less than 1 is used as the iterative coefficient.

[0011] Optionally, in the step of correcting the CIE initial coordinate value according to the iterative direction and the iterative coefficient, at least one of the three coordinate axes in the CIE initial coordinate value is corrected.

[0012] Optionally, the CIE coordinate value in the iterative correction process is obtained by using a color analyzer.

[0013] Optionally, when the color difference between the corrected CIE coordinate value and the CIE target coordinate value meets the preset range, or when the corrected CIE coordinate value reaches the screen gamut boundary and cannot be further adjusted, the iterative correction of the CIE initial coordinate value is completed.

[0014] Optionally, the method further comprises: storing the corrected CIE coordinate value.

[0015] The screen gamut correction method provided by the application firstly determines the target gamut and the initial value of the screen gamut corresponding to a plurality of pixel points, and then calculates the CIE initial coordinate value point by point in the CIE gamut by using a correction algorithm and iterates until the CIE target coordinate value. In this way, the iterative convergence can be accelerated and the error can be reduced, and meanwhile, for the CIE coordinate value which has been iterated at a single point and has a small error, the coordinate value after the iterative correction is transmitted to the CIE initial coordinate value which has not been iterated in proportion, so that the calculation speed can be effectively improved and the calculation time can be saved.

[0016] Further, the screen gamut correction method provided by the present application can improve the consistency of brightness and color in the production process of the screen.

[0017] Further, the screen gamut correction method provided by the present application can improve the consistency of brightness and color in the production process of the screen. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and other objects, features and advantages of the present application will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 A flow chart of the screen gamut correction method according to an embodiment of the present application is shown;

[0020] Figure 2 A flow chart of the iterative correction of the screen gamut correction method according to an embodiment of the present application is shown;

[0021] Figure 3 A schematic diagram of a 3D-LUT node according to an embodiment of the present application is shown;

[0022] Figure 4 A schematic diagram of the transfer of coordinate values according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0023] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the depicted embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0024] For the convenience of understanding the screen gamut correction method provided by the embodiments of the present application, the application scenario of the calibration method provided by the embodiments of the present application is first described below. The calibration method is applied to the screen gamut calibration process, and can be specifically applied to an image processing chip related to image post-processing and image display. The screen gamut calibration refers to making the color performance of a display device close to a standard color under a certain color gamut standard through technical means. For example, under the sRGB color gamut, through gamut calibration, the display red gray scale (255, 0, 0) has a △E less than 2.0 with the sRGB standard red CIE XYZ (0.42146, 0.21267, 0.01922), and there is almost no difference in the sense of sight.

[0025] Brief introduction of related art:

[0026] Color accuracy, also known as color reproduction accuracy, is used to represent the color reproduction capability of a screen, that is, the degree to which the display screen can display each color on the screen. The index of color reproduction accuracy is usually represented by color deviation ΔE. ΔE reflects the difference between the color displayed by the display screen (represented by color coordinates) and the standard color (represented by color coordinates). The smaller the value, the higher the color accuracy of the display screen. The larger the value, the more distorted the color. It can accurately reflect the accuracy of the color performance of the display screen.

[0027] Color coordinates, that is, the coordinates of a color. Through color coordinates, a point in the color space can be determined, which can accurately represent the color.

[0028] Color space is a color model established by people, which represents a certain color by one-dimensional, two-dimensional, three-dimensional or even four-dimensional coordinates. The color range defined by such a coordinate system is the color space.

[0029] Color difference or color accuracy is the difference between the color performance of a color device under a specified color gamut and the standard color. Generally, the smaller the difference, the more accurate the color performance.

[0030] The color coordinates in the present application are, for example, the color coordinates in the CIE 1931 color space. In the study of color perception, CIE 1931 XYZ color space (also known as CIE 1931 color space) is one of the first color spaces defined mathematically. It was created by the International Commission on Illumination (CIE) in 1931. CIE XYZ color space is derived from a series of experiments conducted by W. David Wright (Wright 1928) and John Guild (Guild 1931) in the late 1920s.

[0031] The specific embodiments of the present application are described in further detail below with reference to the accompanying drawings and examples.

[0032] Figure 1 A flow chart of a screen gamut correction method according to an embodiment of the present application is shown; Figure 2 A flow chart of an iterative correction of a screen gamut correction method according to an embodiment of the present application is shown; Figure 3 A 3D-LUT node schematic diagram according to an embodiment of the present application is shown; Figure 4 A coordinate value transfer schematic diagram according to an embodiment of the present application is shown.

[0033] Reference is made to Figure 1 and Figure 2 , the screen gamut correction method of the embodiments of the present application comprises:

[0034] Step S110: Obtain screen gamut initial values and target gamut values of a plurality of pixel points.

[0035] The initial value of the screen gamut of the pixel points comprises a plurality of gray scales, and the screen gamut can also be referred to as an original gamut. For example, the gray scale can be a red gray scale (255, 0, 0), and the number of gray scales can be 5, 10, 20, etc. The screen gamut initial value can be obtained by measurement, for example, a colorimeter can be used to measure the screen gamut initial value of the screen to be calibrated, and then the obtained screen gamut initial value is stored for subsequent use.

[0036] The target gamut value refers to a standard color under a target gamut. The correction process of the screen gamut is to adjust the screen gamut initial value under the standard of the target gamut, so that the color displayed approaches the standard color under the target gamut.

[0037] The plurality of pixel points are selected from 2 n nodes in the LUT table in equal proportions to form a 3D-LUT table of m*m*m, as shown in Figure 3 In the subsequent correction process, the screen gamut is corrected by traversing the m*m*m nodes, so as to obtain ideal color display.

[0038] In this embodiment, the target gamut includes sRGB gamut, P3 gamut, etc.

[0039] Step S120: Convert the screen gamut initial value and the target gamut value of each pixel point to CIE gamut to obtain CIE initial coordinate values and CIE target coordinate values.

[0040] In this step, the obtained screen color gamut initial value and target color gamut value are both converted into coordinate values in the CIE color gamut to obtain corresponding CIE initial coordinate values and CIE target coordinate values. In this embodiment, the screen color gamut initial value is obtained by measurement with a color analyzer.

[0041] Specifically, the screen color gamut initial value and the target color gamut target value can be converted into the CIE initial coordinate values and the CIE target coordinate values through a conversion matrix. The conversion matrix is established as follows:

[0042] (1)

[0043] In the conversion matrix, (o r , o g , o b ) is the screen color gamut initial value, (t r , t g , t b ) is the value of the screen color gamut initial value in the target color gamut, X tr -Z ob is the coordinate of the screen color gamut initial value and the target value of the target color gamut in the CIE color gamut. The above formula (1) gives the matrix formula for mutual conversion of the initial value in the screen color gamut and the target color gamut.

[0044] In this step, the screen color gamut initial value and the target color gamut target value can also be converted into the CIE color gamut through the conversion matrix, and then the iterative correction of the CIE initial coordinate value can be completed in the CIE color gamut.

[0045] In this embodiment, the CIE color gamut is used as the intermediate color gamut, and the iterative correction of the screen initial value is completed in the CIE color gamut. In other embodiments, other color gamuts can also be used as intermediate color gamuts for iterative correction. Different intermediate color gamuts have different conversion formulas when converting the screen color gamut initial value and the target value into coordinate values in the intermediate color gamut.

[0046] In this embodiment, the intermediate color gamut CIE color gamut is specifically, for example, the CIE1931 XYZ color gamut.

[0047] Step S130: Calculate the color difference according to the CIE initial coordinate values and the CIE target coordinate values.

[0048] In this step, when the color difference between the CIE initial coordinate values and the CIE target coordinate values is less than a preset threshold value, the color displayed by the screen color gamut and the target color of the target color gamut have almost no visual difference. Therefore, by calculating the color difference between the CIE initial coordinate values and the CIE target coordinate values, it is determined whether the CIE initial coordinate values need to be calibrated.

[0049] In this embodiment, the color difference between the CIE initial coordinate value and the CIE target coordinate value is ΔE 00 The calculation formula of ΔE 00 is as follows:

[0050] (2)

[0051] In formula (2), L represents the lightness value, C represents the saturation value, and H represents the hue angle value, i.e., the color phase value; ΔL' represents the lightness difference, ΔC' represents the chroma difference, and ΔH' represents the color phase difference.

[0052] K L , K C , and K H are constant parameters, representing parameter factors (correction coefficients related to experimental conditions); under the standard observation condition given by CIE, K L = K C = K H = 1, and when the condition does not conform, the values of the three parameters are determined according to the color difference evaluation condition.

[0053] S L , S C , and S H are weight functions, respectively representing the difference degree in the lightness, saturation, and hue angle directions, defining the length of the elliptical semicircle, and allowing respective adjustments in different regions in the CIE color domain to correct the uniformity of the color space.

[0054] R T is a rotation function, used to correct the deflection of the major axis direction of the tolerance ellipse of the blue region of the color space.

[0055] In this embodiment, the CIE initial coordinate value and the CIE target coordinate value are both expressed in the XYZ coordinate form, and in the calculation of the color difference, conversion to the CIELAB coordinate is required, so as to obtain the lightness value L, the saturation value C, and the hue angle value H. Specifically, the conversion formula is as follows:

[0056] (3)

[0057] (4)

[0059] (5)

[0060] (6)

[0061] (7)

[0062] (8) C = H + S

[0063] Wherein, L, a*, b* represent coordinate parameters in CIELAB color space respectively.

[0064] Step S140: judging whether the color difference is less than the preset threshold value or not.

[0065] In this step, if the color difference is less than the preset threshold value, step S180 is executed; if the color difference is not less than the preset threshold value, step S150 is executed.

[0066] In this embodiment, the preset threshold value is for example 2, according to the color difference formula, the color difference is a number greater than or equal to 0, thus 0≤ΔE 00 <2 is the preset range of the color difference. When the color difference does not meet the preset range, the CIE initial coordinate value is iteratively corrected.

[0067] Step S150: correcting the CIE coordinate value.

[0068] In this embodiment, since the color difference is greater than 2, the CIE coordinate value is corrected. Since the CIE initial coordinate value may need to be continuously corrected after one iteration correction does not meet the preset range, the iteration correction is continuously performed based on the corrected CIE coordinate value. Thus, the CIE coordinate value in this step can represent the CIE initial coordinate value after at least one iteration correction, and the CIE coordinate value includes the CIE initial coordinate value. Hereinafter, the CIE coordinate value is used instead of the CIE initial coordinate value, and the specific correction method is for example as follows.

[0069] Step S151: calculating the difference between the CIE coordinate value and the CIE target coordinate value on three coordinate axes, and determining the iteration correction direction.

[0070] In this step, since the CIE coordinate value is composed of (X, Y, Z), which respectively represent the components of the CIE coordinate value on R, G, B, for example, the X-axis coordinate represents the R component, the Y-axis coordinate represents the G component, and the Z-axis coordinate represents the B component. When calculating the difference between the CIE coordinate value and the CIE target coordinate value in the CIE coordinate, the difference on the three coordinate axes needs to be calculated respectively. Specifically, the difference includes three values ΔX, ΔY, ΔZ, according to the size relationship between ΔX, ΔY, ΔZ and 0, the iteration direction in the correction iteration process can be determined.

[0071] In this embodiment, ΔX = CIE target coordinate value X - CIE coordinate value X. When ΔX > 0, the CIE coordinate value can be iterated in the direction of increasing X value, i.e. increasing R component; when ΔX < 0, the CIE coordinate value can be iterated in the direction of decreasing X value, i.e. decreasing R component; when ΔX = 0, it indicates that the CIE coordinate value X is already the same as the CIE target coordinate value X, and the iteration of X value ends. ΔY = CIE target coordinate value Y - CIE coordinate value Y. When ΔY > 0, the CIE coordinate value can be iterated in the direction of increasing Y value, i.e. increasing G component; when ΔY < 0, the CIE coordinate value can be iterated in the direction of decreasing Y value, i.e. decreasing G component; when ΔY = 0, it indicates that the CIE coordinate value Y is already the same as the CIE target coordinate value Y, and the iteration of Y value ends. ΔZ = CIE target coordinate value Z - CIE coordinate value Z. When ΔZ > 0, the CIE coordinate value can be iterated in the direction of increasing Z value, i.e. increasing B component; when ΔZ < 0, the CIE coordinate value can be iterated in the direction of decreasing Z value, i.e. decreasing B component; when ΔZ = 0, it indicates that the CIE coordinate value Z is already the same as the CIE target coordinate value Z, and the iteration of Z value ends.

[0072] Step S152: determining the iteration coefficient on the same coordinate axis according to the signs of the adjacent two difference values.

[0073] In this step, the iteration coefficient is determined according to the signs of the adjacent two difference values, including ΔX, ΔY and ΔZ. Specifically, if the adjacent two ΔX are both positive or negative, it indicates that the step in the iteration process is too small, and a number greater than 1 needs to be used as the iteration coefficient; if the adjacent two ΔX are one positive and one negative, it indicates that the step in the iteration process is too large, and a number less than 1 needs to be used as the iteration coefficient. Similarly, the iteration coefficients on the Y axis and the Z axis are determined according to the signs of the adjacent two ΔY and the adjacent two ΔZ respectively.

[0074] Step S153: correcting the CIE coordinate value according to the iteration direction and the iteration coefficient.

[0075] In this step, the X, Y and Z coordinates of the CIE coordinate value are iteratively corrected. In the iteration process, if the difference of a certain component is too large while the differences of the remaining components are small, only the component with large difference can be updated. For example, ΔX is large but ΔY and ΔZ are small, at this time, only the R value of the pixel point is adjusted by using ΔX and the R coefficient, and other values can remain unchanged. In other embodiments, ΔX (or ΔY or ΔZ) has a corresponding calculation formula with the R coefficient, the G coefficient and the B coefficient, and then ΔX (or ΔY or ΔZ) can be adjusted according to the formula.

[0076] This method increases the flexibility of adjustment, and makes the current node iterate faster into the error range.

[0077] Step S160: Calculate the error value according to the corrected CIE coordinate value and the CIE target coordinate value.

[0078] In this embodiment, the CIE coordinate value is corrected, that is, the RGB driving signal is updated to change the color gamut display of the screen, that is, each correction corresponds to real-time update of the RGB driving signal.

[0079] In this step, after completing the correction process once, the corrected CIE coordinate value corresponding to the current pixel point is obtained through the color analyzer, and whether further correction is needed is judged by calculating whether the color difference between the corrected CIE coordinate value and the CIE target coordinate value meets the preset range.

[0080] Step S170: Transfer the corrected CIE coordinate value to the CIE initial coordinate value of the next pixel point.

[0081] In this step, since the color difference between the CIE coordinate value and the CIE target coordinate value is less than 2, the calibration of the initial value is completed, and the calibration of the next initial value is performed.

[0082] When calibrating the next initial value, the step of coordinate value transfer is also included. Specifically, coordinate value transfer means that after completing the calibration of an initial value, the calibration of the next initial value is performed, and during this process, the CIE coordinate value corresponding to the calibrated initial value can be transferred to the next initial value in proportion to reduce the iterative calibration process of the next initial value.

[0083] Specifically, an example of coordinate value transfer is: Figure 4 Assuming that point A in the 3D-LUT is the value that has completed the iterative calibration, and point B is the initial value to be calibrated next, according to the relationship between points A and B in the 3D-LUT, it can be understood that the G value and the R value of point B should be the same as those of point A, and only the B value of point A needs to be transferred in proportion, so that the iterative calibration process of the initial value of point B can be accelerated. Similarly, the G value and the B value of point C are the same as those of point A, and only the R value needs to be transferred in proportion; the B value and the R value of point D are the same as those of point A, and only the G value needs to be transferred in proportion. Others can be transferred in proportion according to the positional relationship between the pixel point to be corrected and the pixel point not to be corrected in the 3D-LUT.

[0084] The screen gamut correction method provided by the application firstly determines a target gamut and initial values of screen gamuts corresponding to a plurality of pixel points, then calculates CIE initial coordinate values point by point in a CIE gamut by using a correction algorithm and iterates until CIE target coordinate values. In this way, not only can the iteration convergence be accelerated and the error be reduced, but also, for CIE coordinate values that have been iterated at a single point and have a small error, the iterated and corrected coordinate values are proportionally transmitted to the uniterated CIE initial coordinate values, so that the calculation speed can be effectively improved and the calculation time can be saved.

[0085] Further, the screen gamut correction method provided by the application is that, in the single-point iteration process, XYZ three-channel coordinate values of the CIE initial coordinate values are updated respectively, and if a gap of a certain component is too large while gaps of the rest components are within an error range, only the component with the large gap is updated. In this way, not only is the flexibility of adjustment increased, but also the current node can be iterated to the error range more quickly.

[0086] Further, the screen gamut correction method provided by the application can also improve the consistency of brightness and color in the screen production process.

[0087] According to the embodiments of the application described above, these embodiments do not describe all the details and do not limit the application to the specific embodiments described. Obviously, according to the above description, many modifications and changes can be made. The present description selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well utilize the application and make modifications and uses on the basis of the application. The application is limited only by the claims and their entire scope and equivalents.

Claims

1. A method of screen gamut correction, characterized by, The method comprises the following steps: acquiring initial values of a screen gamut of a plurality of pixels; converting the initial values of the screen gamut of each pixel to CIE color gamut to obtain initial CIE coordinate values and converting target gamut values of each pixel to CIE color gamut to obtain target CIE coordinate values; when a color difference between the initial CIE coordinate values and the target CIE coordinate values exceeds a preset range, iteratively correcting the initial CIE coordinate values; when a color difference between the corrected CIE coordinate values and the target CIE coordinate values meets the preset range, transmitting the corrected CIE coordinate values to initial CIE coordinate values of a next pixel, wherein the step of iteratively correcting the initial CIE coordinate values comprises: calculating differences between the initial CIE coordinate values and the target CIE coordinate values on three coordinate axes to determine an iterative correction direction; determining an iterative coefficient on a same coordinate axis according to signs of two adjacent differences on the same coordinate axis; correcting the initial CIE coordinate values according to the iterative direction and the iterative coefficient.

2. The screen gamut correction method of claim 1, wherein, The method further comprises: judging whether the color difference between the corrected CIE coordinate values and the target CIE coordinate values meets the preset range; if not, iteratively correcting the CIE coordinate values.

3. The screen gamut correction method of claim 2, wherein, The differences are differences between the target CIE coordinate values and the initial CIE coordinate values or the corrected CIE coordinate values on the same coordinate axis.

4. The screen gamut correction method of claim 3, wherein, When any difference is greater than 0, iteratively increasing the coordinate value corresponding to the difference; when any difference is less than 0, iteratively decreasing the coordinate value corresponding to the difference; when any difference is equal to 0, stopping iteration of the coordinate value corresponding to the difference.

5. The screen gamut correction method of claim 4, wherein, On the same coordinate axis, if two adjacent differences are of the same sign, a value greater than 1 is used as the iterative coefficient; if two adjacent differences on the same coordinate axis are not of the same sign, a value less than 1 is used as the iterative coefficient.

6. The screen gamut correction method of claim 1, wherein, In the step of correcting the initial CIE coordinate values according to the iterative direction and the iterative coefficient, at least one of the three coordinate axes in the initial CIE coordinate values is corrected.

7. The screen gamut correction method of claim 2, wherein, A color analyzer is used to acquire the CIE coordinate values in the iterative correction process.

8. The screen gamut correction method of claim 1, wherein, When the color difference between the corrected CIE coordinate values and the target CIE coordinate values meets the preset range, or the corrected CIE coordinate values reach the boundary of the screen gamut and cannot be adjusted any more, the iterative correction of the initial CIE coordinate values is completed.

9. The screen gamut correction method of claim 1, wherein, The method further comprises: storing the corrected CIE coordinate values.

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