TWI283852B - Method for color correction - Google Patents

Abstract

A method for color correction includes selecting a plurality of gray levels and luminance from display source of a display, analyzing the selected data of each light, getting fitting functions by curve fitting each gray level data in each intervals. By using fitting functions to obtain all fitting luminance in the intervals forms a lookup table. For matching the normalized image data to a predetermined target curve, using logarithmic scale plots these two curves in advance, obtaining corrected gray level signals from the lookup table. Outputting these corrected gray level signals to display the gray level distribution on a display. It is applicable to various displays, especially the liquid crystal display.

Description

1283852 V. INSTRUCTION DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to a method of color correction, and more particularly to a color correction method for distributing the distribution state of the original gray scale expression value of image data, the method is The interval matching curve function obtains the gray scale performance value and makes a comparison table. The comparison table quickly obtains the modified gray level signal to provide the display to adjust the gray scale distribution state, and is particularly suitable for the color image processing of the liquid crystal display. [Prior Art] Liquid crystal display (LCD) is a type of flat panel display in optoelectronic products. It has many advantages such as small size, light weight, thin thickness, low power consumption, no flicker, no radiation, etc. In the image processing technology of the display, due to the nature of the liquid crystal molecules, such as viscosity coefficient, dielectric constant and elastic coefficient, there will be problems of excessive response time and image sticking, so an improved driving method is required. Improve image quality, which is the most industrial application value of Active Ma tri X. This driving method is to add an active (Ac ti ve) element to the electrode intersection of the original configuration. The most popular TFT (Thin Film Transistor) technology is one of them. In particular, the TFT type liquid crystal display has an electrode intersection originally disposed on the liquid crystal panel, plus a counter electrode, and the intersection of the three electrodes. Place a film-like active element. Each pixel (P i xe 1 ) of the LCD panel can generate red, green, and blue

1283852

In fact, the liquid crystal itself has no color, the color is generated by the color filter set by the LC Π plate and the light is controlled by the light passing through the image to control the brightness of the color, the degree of brightness and the color. The color filter 1 ^ is generally called the π gray scale value '' (G ray 1 eve move ° inside the liquid crystal display, the gray scale value is generated by the drive element voltage drive' - an 8-bit drive component can generate 2 5 6 The gray-scale voltage, while the middle multi-g 丨 ^ _ wei generates an intermediate voltage value in the driving component, but the liquid crystal light and output are nonlinear, so the voltage must be corrected to obtain a uniform chromaticity distribution of the special 'voltage and pixel The input-output relationship of brightness is approximated by a curve function: $output = input voltage 7, whose parameter is expressed by r (gamma), if the correspondence between f-gradation value and brightness (or gray-scale performance value) is displayed on the ' Then a curve, called "gamma curve" (avoid ammacurve) 'As shown in Figure 1A, when the input grayscale data is divided into r G b dichromatic light, the gamma curve will be as shown in Figure 1B. , usually the original of this gamma curve The order data normalization (η 〇rma 1 ized ) obtains the same gamma curve as the start point and the end point of the curve of the two-color light, as shown in the figure 丄c. Generally, the color correction of the image is based on the normalized gamma curve. In Makou, a driving chip containing a driving method, in order to make the display face the best color shirt performance, that is, the best gamma curve state, the gray scale performance value of the panel must be determined by the color measurement system or device. Measured, and the original grayscale data parent and driver wafer processing; in the prior art, for a multi-light display panel with 8 digits and 7G display, the color measurement system must measure 768 grayscale performance values. Getting a gamma curve is very time consuming, 'cause

1283852 V. INSTRUCTIONS (3) The inventor of this case uses a novel and effective color correction method to greatly shorten the color measurement time, thereby making the color generation faster and more abundant. In addition, for a liquid crystal display, an 8-bit controller can produce 256 shades. If each primary color on the pixel can display 2 5 6 chrominance changes, each pixel can display 2 5 6 X 2 5 6 X 256 colors, which are 1, 6,777, 2 1 6 colors, but this does not meet the requirements of the human eye for color changes, although the display does not see color changes during dynamic display. The difference, but when displayed statically, the human eye will notice that the grayscale change is not smooth enough. In order to solve this problem, the frame rate control (Fr ame Rate C ο ntr ο 1 , FRC ) technology is developed. That is, it is subdivided into several frame materials in the time taken by an image display. When the image data is switched between darker and brighter chromaticity, the pixel can generate intermediate chromaticity during the switching process, so that the grayscale value is more Smooth rendering also makes the color more abundant. If two adjacent pixels are turned on or off at the same time during image color switching, a phenomenon of f1 ickerphe nomenon will occur, which will cause discomfort. Therefore, in order to eliminate this phenomenon, it is necessary to make two pixels different. The gray scale value is generated by correspondingly the original gray scale value of the original gamma curve to a target curve, and the target curve is established according to the characteristics of the liquid crystal display panel, or one of the RGB gamma curves is set. As the target curve, the modified gray-scale signal obtained by the corresponding processing is processed by the FRC technology, and the gray-scale state is displayed on the display. In the prior art, the color processing method is as shown in FIG. The original grayscale value of the gamma curve of light is stepped

Page 10 1283852 V. Description of the invention (4) A gray level representation value corresponding to a target curve, that is, the brightness pointed to in step 2, the brightness of the original pseudo-zero curve is 1 2 8 5 performance, that is, the method of step three, however, the gray scale value is between 1 2 8 and 1 2 9 , so the operation bit needs to be increased from 8 bits to 9 bits by linear interpolation. Find the corresponding gray-scale performance value. If the intermediate gray-scale value is between 1 2 8 .5 and 1 2 9 or between 1 2 8 and 1 2 8 · 5, the operation bit must be raised to More than 10 bits is a burden on hardware resources, and it cannot be quickly and accurately mapped to the target curve by linear interpolation. In view of this, the inventors of the present invention have improved the above-mentioned shortcomings, and have a novel color correction method to make image data processing faster and more colorful. SUMMARY OF THE INVENTION The main object of the present invention is to provide a color correction method for quickly obtaining gray scale performance values of image data and reducing color measurement time. Another object of the present invention is to provide a color correction method for quickly obtaining image-corrected gray-scale performance values, so that the liquid crystal display can correct the gray-scale state of the gray-scale signal distribution, thereby making the display color richer. And does not reduce the resolution of the image. In order to achieve the above object, the color correction method of the present invention separately performs numerical calculation on the selected data of each color light, and obtains a curve curve function of the gray-scale value data in each interval of curve fitting, and obtains the gray in the interval by using the matching curve function. The order value fits the gray scale performance value, and is made into a comparison table, and then the input image gray scale data is normalized.

1283852 V. Invention description (5) After obtaining a gamma curve, the gamma curve is corresponding to a preset target curve. Correspondingly, the two gamma curves are logarithmized, and a modified gray-scale signal is obtained through a comparison table. The modified gray-scale signal is processed by the FRC technology for the gray-scale distribution state of the display, and is particularly suitable for various liquid crystal displays. In order to gain a deeper understanding of this invention, an embodiment will be described in detail later. [Embodiment] Taking a liquid crystal display as an example, in order to correct the brightness display state of the liquid crystal display panel, gray scale values of different color lights are input, and the gray scale performance value of the liquid crystal display panel is measured by a color measuring device or system. In this way, the gamma curve of each color light as shown in FIG. 1B is obtained, and as shown in FIG. 1C after normalization, in the present invention, there are no 256 gray scale values and gray scales for each color light. The performance value is processed, but only the N sets of gray scale data are used to calculate the gamma curve, N is a positive integer and the minimum value is 2. The maximum value is the maximum value of the gray scale value range that the display can display, so the smaller the N value is The faster the measurement speed, but the less accurate the accuracy; the larger the N value, the longer the measurement time, but the accuracy can be improved; for example, the display with RGB tri-color light as the display light source, the best selection is 3 Group 0, as listed below: The gray scale value of red light is: 0,31,63,95,127,159,191,207,223,239,255

Page 12 1283852 (After measuring the gray scale representation value (Q) of the above gray scale value (p), each n group is classified into an interval, η is a positive integer and is greater than or equal to 2, less than or equal to N, if every 2 quantities The gray-scale data is an interval, and the largest of the gray-scale values and gray-scale representation values in the interval is taken, and the logarithm is divided to obtain a gamma parameter function (a): 1ogQmax r — __ logPmax (a) The Ma parameter uses a power function q = apr + b curve to curve all the selected data in the interval to obtain the coefficients a and b, so that each interval has a matching curve function and stores it, using each color of light per interval. Corresponding to the curve function, the grayscale representation value of each grayscale value in the interval is obtained and made into a lookup table, which can be used for subsequent color processing or correction. The right grayscale data of each group is classified into one interval, and the same phase is taken. The maximum value of the gray-scale value of the adjacent two interval and the gray-scale representation value are substituted ((8), and a gamma parameter is obtained. With this parameter, a polynomial Q = aPr + bp + C curve fits all the selected poor materials in the interval. Get the coefficient a, bump, so that each interval gets a curve function and If the n-group gray-scale data is classified as an interval, and n is a positive integer greater than or equal to 2 and less than or equal to Ν, the same is taken as the maximum value of the adjacent two-interval gray-scale value and the gray-scale representation value (a ), find a gamma parameter, and use this parameter as a polynomial (b):

1283852 t V. Description of invention (7) η Q 二 X~卜 + Ή α〇广, m = 2 ( b ) The curve fits all the selected data in the interval, and the coefficients of the function am, a 1 and a 求 are obtained, and Let the value of an - i = 〇, r (7) of each polynomial be determined by the gray level in each interval. The method is to substitute the maximum value of the gray value of the adjacent interval and the gray value of the gray level into the gamma parameter obtained by the function (a). Taking η = 4 as an example, 2 = +3⁄4 , where one of the red light intervals contains gray scale values of 2 0 7 , 2 2 3 , 2 3 9 and 2 5 5 , then r 4 is represented by a gray scale value of 2 5 5 and The gray-scale performance value is determined by the gamma parameter function (a), r 2 is determined by the gray-scale value 2 3 9 and its gray-scale representation value, and r 1 is represented by the gray-scale value 2 2 3 and its gray-scale representation value. Decide, then substitute 4 gray scale values and gray scale performance values into the Q function, and solve the coefficients to obtain the fit curve function of the interval. Use the fit curve function of each color light to obtain the gray scale values in the interval. The grayscale performance values are made into a comparison table for use in subsequent color processing. The above steps can be represented by a flow chart as shown in FIG. 5. By performing this step, a complete comparison table can be established. In other words, the comparison table is represented by different gray level values and corresponding gray scales under different gamma parameters. The value is composed, and the experimental data shows that the error between the gamma curve obtained by the method and the gamma curve obtained by the measurement is smaller than the allowable range of the measuring device, so that it can be known that the curve fits The color correction method not only effectively reduces the time of the measurement display, but also obtains a highly accurate measurement value. The color correction method is applicable to various types of displays, such as liquid crystal displays and projections.

Page 14 1283852 t V. Description of invention (8) Machine, plasma display, etc. In addition, when the original grayscale data signal of the image is input into the display, it is assumed that the gamma curve of the image data is a function of the parameter r: Γ = ( c ) , where X and Y are gray scale values and gray scales of the gray scale signal. Performance value, this gamma curve function is required to correspond to a preset target curve function (d) function, where Y is the target gray scale performance value, r ' is the gamma parameter of the target curve, so that the display can be modified according to the gray The order signal handles the color representation by taking the logarithm of the function (c) ( d ) and let X t = X to get the function: logF = rlogZ ( c,); and \ogYt = rf\ogX ( d,); The two equations are obtained by a simultaneous operation to obtain the function (e): log Yt = log Y (e) The target gray scale representation value Υ t can be obtained from the function (e), and if represented by coordinates, as shown in Fig. 3, the logarithmic coordinate axis The grayscale value and the grayscale representation value respectively, and the value of the function (c')(d') forms a straight line with a slope of r and I·' respectively. When the grayscale value X in of the image data is input, step 1 and Step 2, the target gray scale performance value Y t can be obtained, and after step 3, the slope is a r Find the XQ ut on the horizontal axis and XQ ut as the transition gray scale value X n. Refer to the above comparison table to find the corresponding transition gray scale performance value Υ η; compare Υ η with Y t , if two If the difference is less than a tolerance value, replace the Y t value with the Y n value, and replace the target gray scale value X t with the transition gray value X 11 , otherwise repeat the above steps until the difference between Y 11 and Y t is small

Page 15 1283852

V. Description of invention (9) ^ = Xu error value' will then be used to represent the target gray scale value xt. "A FRc^ will correct the grayscale tK number table ^, white = step flow chart as the sixth As shown in the figure, the accuracy determined by this step can be determined according to the different gamma ray fire = = gray: value and: corresponding gray scale performance value provided by the above-mentioned comparison table, which is not subject to hardware resources: The color level is more abundant, and the original gray level resource 1 = the modified gray level signal can be correspondingly made into a comparison table according to the gray scale distribution state. % as the f according to Fig. 4, the device with 9 bits can be linearly The gray scale value of interpolation 2 8 . 5 is expressed, but if the gray scale is broken into the approximate value 丄 2 8 · 5 , and " 丄 2 8 5 to output 廿: will:: performance, the method of this case can be directly Presented by the grayscale value worker 8, and then processed by the FRC technology, the accurate gray is obtained. Therefore, the present invention has the following advantages: 1. The color f correction method of the present invention makes the display color measurement and The difference is less than the allowable range of the device and the value is awarded. Qiao α 1 soil industry competition 2 5 hair: the J color correction method makes the color table b and does not reduce the analysis of the picture Tang, care for the + ^ and the horse bean preparation, feeling. U makes the color of the display not vivid, and the stereoscopic combination is described above. The invention can achieve the method of pre-predicting the display calibration process quickly, the color is richer and is provided for one method, and the value of the industry is highly utilized. 16 pages 1283852 Brief description of the diagram [Simple description of the diagram] Figure 1A is a schematic diagram of the conventional gamma curve. Figure 1 B is a schematic diagram of the original gamma curve of different colored lights. Figure 1 C is a schematic diagram of the normalized gamma curve of different colored lights. Figure 2 is a schematic diagram of a method in which a conventional gamma curve corresponds to a target curve. Figure 3 is a schematic diagram showing the steps of determining the target gray scale performance value of the target function curve by the input gray scale value of the color correction method of the present invention. Fig. 4 is a schematic view showing a comparison of the method of color correction of the present invention with the method of the prior art. Fig. 5 is a flow chart showing a comparison table of the gray scale performance values of the gray scale values of the respective colors in the method of color correction of the present invention. Figure 6 is a flow chart showing the modified gray scale signal of each color light outputted by the color correction method of the present invention.

Page 17

Claims (1)

1283852 6. Patent application scope 1. A method for color correction, the method comprises the following steps: (1) measuring the gray scale value and gray scale performance value of the display light source by the color measurement system; (2) gray scale value and gray scale The order representation value is normalized (η 〇rma 1 ized ), and N sets of gray scale values and gray scale representation values are selected, N is a positive integer, the minimum value is 2, and the maximum value is the maximum range of gray scale values that the display can display. (3) classify the selected value of the above steps into an interval, η is a positive integer and greater than or equal to 2, less than or equal to Ν; (4) grayscale value (Ρ) and grayscale representation value of each interval (Q) After the logarithm is divided, the gamma parameter (gamma) is obtained: log?, according to the gamma parameter, all the selected data in the interval are matched by a function curve, so that each interval has a matching curve. The function y (5) uses the fit curve function of each color light to obtain the fit gray scale representation value of each gray scale value in the interval, and makes the corresponding numerical sequence of the gray scale value and the corresponding gray scale expression value into a comparison table ( Lookup table); (6) original image Order Data normalization (η o r m a 1 i z e d), respectively comprising a light gray color gamma curve value (X) and the level performance value (Y) of the gray scale signal (gamma curve), the gamma curve function Page 18 1283852 VI. The scope of the patent application is i7 = ' Γ is the gamma number; (7) the gamma curve function is r = image gray level signal pair jp*, should be a preset target curve function ¥ = A , that is, let X t be equal to X, and obtain a modified gray-scale signal by approximation method. The steps are as follows: (a) The gamma curve function and the target curve function are respectively digitized by log Yt = -log Y, so r, thereby obtaining the target gray scale expression value Y t ; (b) referring to the comparison table with a transition gray scale value X n to obtain a corresponding transition gray scale representation value Y n ; (c) transition gray scale The performance value Y 11 is compared with the target gray scale performance value Y t . If the difference between the two is less than a tolerance value, the Y t value is replaced by Y n , and the target gray scale value X t is replaced by the transition gray scale value X 11 . If the difference between the two is not less than an allowable error value, repeat steps (a) through (c), (d) output the modified gray-scale signal containing the target gray-scale value X t ; and (8) correct the gray scale The signal output enables the display to display the grayscale distribution state according to the modified gray scale signal. 2. A method of color correction as described in claim 1 of the patent application, wherein Page 19 1283852 VI 3 4 5 Patent application range The display source is R G B (red, green and blue) three-color light. • The method of color correction as described in item 1 of the patent application section. Each interval takes the maximum value of the adjacent grayscale value and the grayscale representation value r = 1〇g to obtain the gamma parameter, ie log Prax. The method of color correction according to claim 1, wherein the η function is a polynomial based on gamma parameters 2 = % ' η is a positive integer greater than or equal to 2, less than or equal to N, am, a, and a ◦ The coefficient of this function, and let a of each polynomial. The value of i = 〇 ’ r m is determined by the grayscale value in each interval. A color correction comparison table manufacturing method in a color correction method, the method comprising: (1) measuring a gray scale value and a gray scale performance value of a display display source by a color measurement system; (2) setting a gray scale value and The grayscale representation value is normalized (η 〇rma 1 1 zed ), and N sets of grayscale values and grayscale representation values are selected, 1^ is a positive integer, the minimum value is 2, and the maximum value is the grayscale value that the display can display. (3) The selected value of the above steps is divided into an interval, n is a positive integer and greater than or equal to 2, less than or equal to Ν; (4) the grayscale value (Ρ) and gray of each interval The order performance value (q) is divided by the logarithm and the gamma parameter (gamma) is obtained. Page 20 1283852 VI. Application scope ··匕#, according to this gamma parameter, a curve curve fits all the selected data in the interval to make each interval get a curve function; and (5) use each color The fit curve function of each interval of light obtains the gray scale representation value of each gray scale value in the interval, and makes the corresponding numerical sequence of the gray scale value and the gray scale representation value into a lookup table. 6. If the color correction comparison table preparation method described in item 5 of the patent application scope is used, the maximum ^^ log Q ^ value of the adjacent gray scale value and the gray scale expression value is taken in each interval to obtain the gamma parameter. , that is, "a log corpse coffee. 7. A method for making a color correction reference table as described in claim 5, wherein the function is based on a gamma parameter and the polynomial η ' η is greater than 2, less than or equal to ν, integer, am, ai, and a Q are the coefficients of this function, and let the value of a n_P 〇, Γ (1) of each polynomial be determined by the gray scale value in each interval. 8. As in the fifth paragraph of the patent application scope The color correction comparison table preparation method is described in which the xenon light source is red, green and blue, and the gray scale value of the red light is 0, 31, 63, 9 5, 1 27, 1 59, 191, 20 7, 223, 239, 255; The gray scale of the green light is ·· 3丨,6 3,9 5,丨2 7,丨5 9,丨9丨,2 〇 7 Page 21, 1283852 VI. The scope of application for patents 223, 2 3 9, 2 5 5; and the gray scale of the blue light are: 3 0,6 3,9 6,1 2 9,1 6 2,1 9 5, 2 1 5,2 3 5,2 5 5. 9. The color correction reference sheet manufacturing method according to claim 5, wherein the display is a liquid crystal display. 1 0. The color correction reference sheet manufacturing method according to claim 5, wherein the display is a projector. 1 1 . The color correction reference sheet manufacturing method according to claim 5, wherein the display is a plasma display (P 1 a s m a Disp lay Panel). Page 22 1283852 No 1283852 VI. Designation of Representative Representatives (1) The representative figure of this case is: ____________ (2), the representative symbol of the representative figure of this case is simple: