A method and device for controlling RGB-LED with thermal coupling resistance

Abstract

The present invention discloses a RGB-LED control method and device with anti-thermal coupling. Under the influence of the thermal energy of two color light sources, a three-color stimulus value third-order model of monochromatic light that changes smoothly with the brightness of another monochromatic light source is established; then the three-color stimulus value coordinates of the three primary colors of R, G, and B are obtained according to the three-color stimulus value third-order model; finally, the three-color stimulus value coordinates of the target color are obtained based on the three-color stimulus value coordinates of the three primary colors, so as to control the three primary color diodes of the RGB-LED to mix the target color. Compared with the prior art, this method improves the smoothness of the result by modeling through a third-order function and introducing piecewise linear interpolation, Hermite function, and spline curve, so that the pattern can be displayed naturally and accurately under the influence of thermal coupling, that is, the color accuracy of the RGB-LED display color is improved.

Description

Technical Field

[0001] The present invention relates to an LED control method and device, and in particular to an LED color control method and device. Background Art

[0002] Nowadays, RGB-LED technology has been widely used in all aspects of life, such as advertising screens at shopping mall entrances, atmosphere lights on train berths, background stage screens for evening parties, traffic display screens at intersections, etc. Users require that the display screens can accurately display the target pattern and switch patterns quickly and naturally. The basic principle is to mix the three primary color diodes of RGB-LED into the target color through a preset model, and then combine the RGB-LED into a large screen to form the target image.

[0003] Ambient temperature is one of the important factors that affect the junction temperature of LEDs. According to experimental data, the wavelength changes by 0.2-0.3nm for every degree of temperature change. Wavelength drift will cause problems with color correction.

[0004] In a single light source, three diodes share one heat sink. Different light intensity requirements will cause different changes in the temperature of the diodes. Therefore, it is necessary to consider the color drift caused by the mutual influence of thermal coupling between each light source. Furthermore, the heat sink has a limited service life. The thermal coupling phenomenon will be more serious after long-term use, and there will inevitably be color deviation, which will require the replacement of the heat sink. Therefore, it is necessary to propose a method to improve the color drift problem caused by thermal coupling, improve color accuracy, and extend the service life of the heat sink.

[0005] The existing solution is to use a second-order nonlinear model combined with an area interpolation method to obtain a three-color stimulus value model and the three-color stimulus value coordinates of the three primary colors. The second-order nonlinear model is directly sent to the sRGB space through the cloud or APP and simply converted into a PWM duty cycle or grayscale value. The target color is mixed through the three three-primary color diodes of the RGB-LED. This method will cause some inaccurate color mixing, and the area interpolation method used in this method will produce the Runge phenomenon, resulting in an unnatural color transition when the pattern is switched, and the ideal target color effect cannot be achieved.

[0006] In summary, the existing technology has limited effect on improving the thermal coupling of RGB-LEDs. Summary of the invention

[0007] Purpose of the invention: In view of the above-mentioned prior art, a RGB-LED control method and device with resistance to thermal coupling are proposed to achieve a natural and accurate display of the target pattern under the influence of thermal coupling.

[0008] Technical solution: A heat-coupling-resistant RGB-LED control method, comprising: first, for a single color among the three primary colors of R, G, and B, under the influence of the thermal energy of the other two color light sources, using the CIE-XYZ color space, a three-color stimulus value third-order model that changes smoothly with the brightness D of the monochromatic light source is established; then, the three-color stimulus value coordinates of the three primary colors are obtained according to the three-color stimulus value third-order model; finally, the three-color stimulus value coordinates of the target color are obtained based on the three-color stimulus value coordinates of the three primary colors, so as to control the three-primary color diodes of the RGB-LED to mix the target color.

[0009] Furthermore, the third-order model of the three-color stimulus values ​​adopts a third-order polynomial function. For any primary color, the steps of solving the coefficients of each order in the corresponding third-order polynomial function include: first, obtaining the first-order polynomial function relationship between the coefficients of each order in the third-order polynomial function by piecewise linear interpolation; then, based on the first-order polynomial function relationship, solving the values ​​of the coefficients of each order in the third-order polynomial function by piecewise Hermite interpolation.

[0010] Furthermore, the specific steps of solving the coefficients by the piecewise Hermite interpolation method include: first, obtaining a number of discrete data by experiment, wherein the discrete data is composed of the brightness of a monochromatic light source and the three-color stimulus values ​​measured by an instrument; then, fitting a B-spline curve based on the discrete data, and calculating the derivatives of the three-color stimulus values ​​in each discrete data point by the B-spline curve; then, substituting the three-color stimulus values ​​and their derivatives in the discrete data points into the Hermite interpolation function to obtain a three-color stimulus value function curve that changes smoothly with the brightness D of the monochromatic light source; finally, sampling the three-color stimulus value function curve, substituting the sampled values ​​into the first-order polynomial function relationship obtained by the piecewise linear interpolation method, and solving to obtain the values ​​of each order coefficient in the three-color stimulus value third-order model, thereby constructing the three-color stimulus value third-order model corresponding to the single primary color light.

[0011] Furthermore, the step of obtaining the discrete data through experiments specifically includes: shielding two color light sources in the three-primary color LED light source that shares a heat sink with a black blackout cloth, so that thermal energy affects the other color light source without leaking the light intensity and color; controlling the constant current drive of the other color light source, adjusting the brightness of the two shielded color light sources through the driver, measuring the brightness of the other color light source under the influence of different thermal energy intensities of the two colors, and simultaneously measuring the three-color stimulation value of the other color light in the process through a colorimeter; and obtaining a number of discrete data corresponding to the single primary color by repeatedly changing the brightness of the other color light source.

[0012] A RGB-LED control device with resistance to thermal coupling comprises a memory, a processor and a computer program stored in the memory and executable on the processor. The processor executes the program to implement the RGB-LED control method with resistance to thermal coupling.

[0013] Beneficial effect: Under the influence of the thermal energy of two color light sources, the method of the present invention establishes a three-order model of the three-color stimulus values ​​of monochromatic light that changes smoothly with the brightness of another monochromatic light source; then the three-color stimulus value coordinates of the three primary colors of R, G, and B are obtained according to the three-color stimulus value three-order model; finally, the three-color stimulus value coordinates of the target color are obtained based on the three-color stimulus value coordinates of the three primary colors, thereby controlling the three-primary color diodes of the RGB-LED to mix the target color. Compared with the prior art mentioned in the background technology, this method improves the smoothness of the result by modeling with a third-order function and introducing piecewise linear interpolation, Hermite function and spline curve, so that the pattern can be displayed naturally and accurately under the influence of thermal coupling, that is, the color accuracy of the RGB-LED display color is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of the method of the present invention;

[0015] Figure 2 is the function model obtained by piecewise linear interpolation;

[0016] Figure 3 It is a schematic diagram of an experiment of the influence of different light intensities on color coordinates of the present invention;

[0017] Figure 4 It is the function model obtained by Hermite interpolation of the present invention;

[0018] Figure 5 This is a diagram showing the difference between the final target color coordinates and the ideal values ​​of the existing method and the method of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further explained below in conjunction with the accompanying drawings.

[0020] For three-primary-color LED light sources that share a heat sink, different light intensities will cause different changes in the temperature of the LED diode. Therefore, it is necessary to consider the color drift problem caused by the mutual influence of thermal coupling between LED light sources.

[0021] The invention discloses an RGB-LED control method with heat coupling resistance. The target color is composed of mixed colors of three primary color light sources of R, G and B. The CIE-XYZ color space is adopted. For one single color among R, G and B, under the influence of the heat energy of the other two color light sources, a three-color stimulus value three-order model of the monochromatic light is established, which changes smoothly with the brightness D of the monochromatic light source. Then, the three-color stimulus value coordinates of the three primary colors of R, G and B are obtained according to the three-color stimulus value three-order model. The three-color stimulus value coordinates of the target color are obtained based on the three-color stimulus value coordinates of the three primary colors, so as to control the three primary color diodes of the RGB-LED to mix the target color.

[0022] like Figure 1 As shown, a RGB-LED control method with anti-thermal coupling, the specific steps are as follows:

[0023] Step 1: Establish a three-order model of the tristimulus values ​​of monochromatic light that changes smoothly with the brightness D of the monochromatic light source.

[0024] The third-order model of tristimulus values ​​adopts a nonlinear model of a third-order polynomial function. In this embodiment, red is taken as an example for explanation. The third-order model of tristimulus values ​​corresponding to red is expressed as shown in formula (1):

[0025]

[0026] In the formula, X R ( D r , D g , D b ), Y R ( D r , D g , D b ), Z R ( D r , D g , D b ) represents the tristimulus value coordinates of the red X-axis, Y-axis, and Z-axis; D r , D g , D b Respectively represent the brightness of red, green and blue light sources; α RX ( D g ,D b ), β RX ( D g , D b ), λ RX ( D g , D b ) represent the coefficients of the duty cycle of green and blue light sources on the X-axis of the CIE-XYZ color space, α RY ( D g , D b ), β RY ( D g , D b ), λ RY ( D g , D b ) represent the coefficients of various orders related to the duty cycle of green and blue light sources on the Y axis of the CIE-XYZ color space, α RZ ( D g , D b ), β RZ ( D g , D b ), λ RZ ( D g , D b ) represent the various order coefficients related to the duty cycle of the green and blue light sources on the Z axis of the CIE-XYZ color space.

[0027] In the present invention, the brightness of the light source is normalized to between 0 and 1. When D=0, the light source is completely turned off, and when D=1, the light source is turned on at full power, at which time the brightness is the maximum value.

[0028] Step 2: Solve the coefficients of each order in equation (1) by piecewise linear interpolation to obtain the coefficients α , β , λ The first-order polynomial function relationship between .

[0029] Since the proposed three-color stimulus value third-order model belongs to a high-order polynomial function, the Runge phenomenon will occur during the interpolation solution, that is, when using a high-order polynomial for interpolation, as the number of interpolation increases, the interpolation result will gradually deviate from the original function, resulting in inaccurate results. Therefore, this method introduces piecewise linear interpolation to solve this problem. Specifically, taking the X-axis of the three-color stimulus value third-order model as an example, in the brightness D r0 The two nodes on the left and right ( D r1 , X R1 )、( D r2 , X R2 ) constitutes the interval ( D r1 , D r2 ) to perform linear interpolation, and then substitute the interpolation result into formula (1) to obtain the coefficients of the third-order polynomial function corresponding to the segment α , β , λ The first-order polynomial function relationship between . Among them, X R1 , X R2 Indicates brightness D r1 , D r2 The corresponding X-axis tristimulus values.

[0030] Further calculation based on the first-order polynomial function relationship can yield the following Figure 2 The third-order model curve of the three-color stimulus values ​​on the X-axis shown in the figure will lose the smoothness of the original function due to the model obtained by using piecewise linear interpolation. When this model is used for RGB-LED three-primary color mixing control, the color transition of the LED screen will not be natural enough.

[0031] Step 3: In order to solve the problem of unnatural transition caused by piecewise linear interpolation, this method further solves the values ​​of each order coefficient in the third-order polynomial function by piecewise Hermite interpolation. This step is also explained by taking the X-axis of the third-order model of tristimulus values ​​as an example.

[0032] First, some discrete data are obtained through experiments. The specific steps are as follows:

[0033] S1: Figure 3The blue and green light sources in the three-primary color LED light source sharing a heat sink are shielded by a black shading cloth, so that the red light source is not affected by heat energy without leaking the light intensity and color. The red light source is driven at a constant current, and the brightness of the blue and green light sources is adjusted by the driver, that is, the D g and D b The size of the red light source is measured under the influence of different thermal energy intensities of the blue light source and the green light source. D r At the same time, the X-axis tristimulus value of the red light in the process is measured by a colorimeter X R .

[0034] In this step, the monochromatic light source tube is connected to the PWM controller through a flat wire, and a current of 50mA is used for constant current driving of the red light source.

[0035] S2: Change the brightness of the red light source multiple times and repeat step S1 to obtain a number of discrete data corresponding to the red light ( D ri , X Ri ), where 0< i ≤ n , i is an integer, n Represents the number of discrete data obtained in the experiment. Then, a B-spline curve is fitted based on the obtained discrete data. The B-spline curve is a piecewise continuous polynomial and is finitely differentiable on the entire curve, which can ensure that the discrete data points on the entire curve are differentiable in the subsequent Hermite interpolation. Then, the derivative of the tristimulus value at each discrete data point is calculated by fitting the B-spline curve. X Ri ', the three color stimulus values ​​in each discrete data point X Ri and its derivative X Ri 'Substitute into the Hermite interpolation function and get the brightness of the red light source D r Changing and smoothly changing red light X-axis tristimulus values X R Function curve. Sample the function curve and substitute the sampled value into the value obtained in step 2. α , β , λ In the first-order polynomial function relationship between , the values ​​of the coefficients of each order in the X-axis of the three-order model of the three-color stimulus values ​​are solved, so as to construct the three-order model of the X-axis three-color stimulus values ​​corresponding to red light, such as Figure 4 shown.

[0036] Step 4: According to the methods of step 2 and step 3, the values ​​of the coefficients of each order corresponding to the Y axis and the Z axis of the three-order model of the three-color stimulus values ​​are respectively solved, thereby completing the establishment of the three-order model of the three-color stimulus values ​​corresponding to red light.

[0037] Step 5: Establish a three-order model of the three color stimulus values ​​corresponding to green light and blue light according to the methods of steps 1 and 4.

[0038] Step 6: Obtain the tristimulus value coordinates of the three primary colors R, G, and B according to the three-order tristimulus value model, and substitute them into equation (2) to obtain the tristimulus value coordinates of the target color O.

[0039]

[0040] in,( X R , Y R , Z R ) represents the tristimulus value coordinates of red, ( X B , Y B , Z B ) represents the tristimulus value coordinates of blue, ( X G , Y G , Z G ) represents the tristimulus value coordinates of green, ( X O , Y O , Z O ) represents the tristimulus value coordinates of the target color O.

[0041] Step 7: According to the three-color stimulus value coordinates of the target color O, the three primary color diodes of the RGB-LED are controlled to mix the target color.

[0042] like Figure 5 It can be seen that the solid line is the color accuracy of the existing second-order nonlinear model combined with the regional interpolation method, and the dotted line is the color accuracy of the method of the present invention. The lower the color accuracy, the higher the color accuracy, and the ideal target color accuracy is 0. As can be seen from the figure, the color accuracy obtained by this method is much lower than the existing method, basically stable below the value of 2, and the color accuracy fluctuation obtained in each experiment is also smaller, which means that the average quality of the result pattern obtained by this method is more stable, the probability of pattern mottle is reduced, and the effect that the user wants can be obtained more stably and accurately. The color accuracy index Delta-E is up to 73% compared with the existing technology.

[0043] A RGB-LED control device with anti-thermal coupling performance includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the program to implement the above-mentioned RGB-LED control method with anti-thermal coupling performance.

[0044] In summary, the method of the present invention can solve the problem of unnatural pattern switching while reducing the Runge phenomenon caused by high-order modeling, greatly improve the color drift problem caused by thermal coupling, and extend the service life of the radiator.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A RGB-LED control method with anti-thermal coupling, characterized in that: include: Firstly, for one of the three primary colors of R, G, and B, under the influence of the heat energy of the other two color light sources, a three-color stimulus value three-order model that changes smoothly with the brightness D of the monochromatic light source is established using the CIE-XYZ color space; then, the three-color stimulus value coordinates of the three primary colors are obtained according to the three-color stimulus value three-order model; finally, the three-color stimulus value coordinates of the target color are obtained based on the three-color stimulus value coordinates of the three primary colors, so as to control the three-primary color diodes of the RGB-LED to mix the target color; The three-order model of tristimulus values ​​adopts a third-order polynomial function. For any primary color, the steps of solving the coefficients of each order in the corresponding third-order polynomial function include: first, obtaining the first-order polynomial function relationship between the coefficients of each order in the third-order polynomial function by piecewise linear interpolation; then, based on the first-order polynomial function relationship, solving the value of each coefficient in the third-order polynomial function by piecewise Hermite interpolation; The specific steps of solving the coefficients by the piecewise Hermite interpolation method include: first, obtaining a number of discrete data by experiment, wherein the discrete data is composed of the brightness of a monochromatic light source and the three-color stimulus values ​​measured by an instrument; then, fitting a B-spline curve based on the discrete data, and calculating the derivatives of the three-color stimulus values ​​in each discrete data point by the B-spline curve; then, substituting the three-color stimulus values ​​and their derivatives in the discrete data points into the Hermite interpolation function, and obtaining a three-color stimulus value function curve that changes smoothly with the brightness D of the monochromatic light source; finally, sampling the three-color stimulus value function curve, substituting the sampled values ​​into the first-order polynomial function relationship obtained by the piecewise linear interpolation method, and solving to obtain the values ​​of each order coefficient in the three-color stimulus value third-order model, thereby constructing the three-color stimulus value third-order model corresponding to the single primary color light; The steps of obtaining the discrete data through experiments specifically include: shielding two color light sources in the three-primary color LED light source that share a heat sink with a black shading cloth, so that thermal energy affects the other color light source without leaking the light intensity and color; controlling the constant current drive of the other color light source, adjusting the brightness of the two shielded color light sources through the driver, measuring the brightness of the other color light source under the influence of different thermal energy intensities of the two colors, and obtaining the three-color stimulation value of the other color light in the process through a colorimeter; and obtaining a number of discrete data corresponding to the single primary color by repeatedly changing the brightness of the other color light source.

2. A RGB-LED control device with anti-thermal coupling, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the RGB-LED control method with anti-thermal coupling as claimed in claim 1.

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