A method for calibrating the brightness of a light

Abstract

The present invention discloses a method for calibrating the brightness of a light source. According to the test of a standard sample, the corresponding relationships between the gray scale value of a photo and the cold machine brightness, and between the cold machine brightness and the hot machine brightness are determined. Thus, by taking a photo of the light source to be calibrated through a camera, the gray scale value of the photo brightness can be obtained to determine the hot machine brightness of the light source to be measured. According to the deviation between it and the target brightness value, the PWM duty cycle is adjusted, thereby realizing the calibration of the light source. The calibration equipment has low cost and high efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle detection, and in particular to a method for calibrating the brightness of vehicle lights. Background Art

[0002] With the improvement of people's demand for vehicle safety, vehicle lights (including LED lights, backlights, screens, etc.) are composed of multiple tiny lights. At the beginning of the design, they are defaulted to have the same brightness and can only achieve basic prompting and lighting initially. As environmental protection and intelligence become deeply rooted in people's hearts, the transformation of vehicle lights towards environmental protection and intelligent lights has gradually become a trend. It has brought a subversive change to the vehicle lighting system. More and more projection imaging technologies are applied in the field of vehicle lights, making the brightness requirements of vehicle lights more precise and controllable. Since most light sources themselves have temperature characteristics, after the vehicle lights are turned on, it usually takes a period of time (i.e., the warm-up state) for the light brightness to stabilize, and the value after stabilization is the value suitable for the current environment. In actual production, in order to pursue production efficiency while ensuring that the brightness of each light source meets the design requirements, it is necessary to complete the calibration of the light brightness within a very short time after the vehicle lights are turned on (i.e., the cold start state). The existing online calibration of vehicle light brightness usually uses a brightness meter calibration system for real-time calibration. The calibration principle of the brightness meter calibration system is: the brightness meter measures the current brightness value and transmits the current brightness value to the computer. The computer compares the current brightness value with the target brightness value to be adjusted. If the comparison result shows that the corresponding brightness value exceeds / falls below the required target brightness range, the initial PWM (Pulse Width Modulation) is adjusted downward / upward by a preset amplitude. The brightness meter senses the current brightness value again and transmits it to the computer for comparison with the target brightness value. The above process is repeated until the current brightness value is within the range of the target brightness value, and thus the calibration of the brightness is completed. Because of its high calibration accuracy, it is widely used, but the circuit system of the brightness meter calibration system is complex and expensive. At the same time, due to the large number of products to be calibrated and the large quantity, the calibration failure rate of its system is relatively high under long-term and high-intensity calibration work. In addition, its calibration process often requires multiple repetitions, multiple measurements are required during calibration, a large amount of system data processing is involved, and the time is slightly longer, and the efficiency is still slightly low. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for calibrating light brightness with low cost, high efficiency, and low failure rate.

[0004] A method for calibrating light brightness includes the following steps:

[0005] A. Test the brightness of the standard sample under the cold start state and the warm-up state, and establish a one-to-one correspondence first mapping relationship between the warm-up brightness and the cold start brightness;

[0006] Establish a calculation model among the cold machine brightness, hot machine brightness, cold machine PWM (pulse width modulation) duty cycle, and hot machine PWM duty cycle tested based on the standard sample;

[0007] The brightness control module controls the standard sample to work at different PWM duty cycles. In the cold machine state, use a brightness meter to measure its brightness and a camera to measure the gray scale value of its photo, and establish a one-to-one corresponding second mapping relationship between the standard brightness and the standard gray scale value based on this test data;

[0008] B. Set the initial PWM duty cycle. The brightness control module controls the light source to be calibrated to work according to the initial PWM duty cycle, and obtain the gray scale value of the photo of the light source to be measured at this time through the camera;

[0009] C. Determine the standard brightness value according to the second mapping relationship based on the obtained gray scale value; determine the hot machine brightness value according to the first mapping relationship based on the standard brightness value; compare the hot machine brightness value with the target hot machine brightness value to judge whether its brightness deviation value is within the threshold range;

[0010] D. If the brightness deviation value is within the threshold range, the calibration is completed; if the brightness deviation value exceeds the threshold, calculate the theoretical hot machine PWM duty cycle according to the calculation model established in step A, and the brightness control module controls the light source to be calibrated to work according to this theoretical hot machine PWM duty cycle;

[0011] E. Obtain the gray scale value of the photo of the light source to be measured at this time through the camera, determine the standard brightness value according to the second mapping relationship based on the obtained gray scale value, determine the hot machine brightness value according to the first mapping relationship based on the standard brightness value, and compare the hot machine brightness value with the target hot machine brightness value to judge whether its brightness deviation value is within the threshold range;

[0012] F. If it is within the threshold range, the calibration is completed; if it is not within the threshold range, fine-tune the PWM duty cycle in an up-and-down adjustment manner, increase it if it is too large and decrease it if it is too small, and then control the light source to be measured to work according to the adjusted PWM duty cycle, and return to step E.

[0013] As a further improvement of the present invention, in step A, the brightness control module determines the adjustment step of the PWM duty cycle according to the calibration accuracy, and measures the corresponding cold machine brightness and the gray scale value of the photo corresponding to the cold machine brightness, the hot machine brightness and the gray scale value of the photo corresponding to the hot machine brightness for each step.

[0014] As a further improvement of the present invention, the calculation model established among the cold machine brightness, hot machine brightness, cold machine PWM duty cycle, and hot machine PWM tested based on the standard sample in step A is as follows:

[0015] Among them, A, B, and C are constants; PWM (warm) is the PWM value for the heat engine test; Cd (warm) is the brightness value for the heat engine test; PWM (cold) is the PWM value for the cold engine test; Cd (cold) is the brightness value for the cold engine test. The values of A, B, and C are obtained by substituting the cold engine brightness, heat engine brightness, cold engine PWM duty cycle, and heat engine PWM duty cycle data from the standard sample test into the calculation model for calculation.

[0016] A method for calibrating the brightness of a light source. The software and hardware driving environment of the standard sample is the same as that of the light source to be tested. Through the test of the standard sample, the corresponding relationship between the standard brightness and the standard gray scale value of the light source, as well as the corresponding relationship between the cold machine brightness and the hot machine brightness, are established. Thus, when detecting the light source to be tested, the standard brightness value in the cold machine state corresponding to it can be obtained by the gray scale value of the photo of the light source taken by the camera, and the brightness value in the hot machine state can be indirectly obtained. Then, by comparing with the target brightness value, it can be determined whether the brightness meets the requirements. When it does not meet the requirements, the PWM duty cycle [PWM (warm)] in the hot machine state of the target brightness can be directly calculated through the determined calculation model, which can be called the theoretical PWM duty cycle. Then, the light source to be tested is controlled to work again with this theoretical PWM duty cycle. Since the characteristics of the light source to be tested are basically the same as those of the standard light source, usually driving the product with the theoretical PWM duty cycle can directly reach within the deviation threshold range of the target brightness value to complete the calibration. However, due to factors such as the deviation of the heat dissipation and light emission caused by the deviation of the material size and installation position during the production process (when the total amount of heat and light emission of the light source remains unchanged, the light emission will decrease when the heat dissipation effect deviates), there will be a certain deviation between the PWM duty cycle value and the brightness relationship of the actual light source to be tested and the standard sample. Therefore, after driving the product with the theoretical PWM value, there may still be a situation where the brightness is not within the deviation threshold range of the target brightness value. So, it is necessary to test the brightness value again to ensure the calibration of the light source. Since this situation is a case where the characteristics of the light source to be tested deviate from those of the standard light source, at this time, the calculation model is no longer used to determine the PWM duty cycle, but the PWM duty cycle is calibrated by the conventional method of fine-tuning up and down. For the method for calibrating the brightness of the light source described in the present invention, since the mapping relationship between the gray scale value and the brightness of the photo of the light source is established through the test of the standard sample, the brightness of the light source can be determined by obtaining the gray scale value of the photo of the light source, and there is no need to use a brightness meter, which greatly reduces the equipment cost. Although the brightness calibration of the light source requires calibrating the hot machine brightness in the hot machine state, because the method for calibrating the brightness of the light source according to the present invention establishes the mapping relationship between the cold machine brightness and the hot machine brightness through the test of the standard sample, the brightness calibration of the light source is realized in the cold machine state, which greatly reduces the calibration time and improves the calibration efficiency. In addition, the method for calibrating the brightness of the light source establishes a calculation model based on the cold machine brightness, hot machine brightness, cold machine PWM duty cycle, and hot machine PWM duty cycle tested by the standard sample. When the brightness control module controls the light source to work with the initial PWM duty cycle and the brightness is not within the threshold deviation range, it can calculate the theoretical PWM duty cycle corresponding to the target brightness of the standard light source through the calculation model, and then control the light source to work again according to this theoretical PWM duty cycle for calibration. Since the characteristics of the standard light source and the light source to be tested are usually the same or relatively close, when the light source to be tested is controlled to work with this theoretical PWM duty cycle, its brightness will often be close to the target brightness. Therefore, in most cases, the calibration can be successful with this method.Even if the calibration is not successful and there are still deviations, the normal deviations are usually small. Then, through the method of fine-tuning up and down, the calibration of the light source can be quickly achieved. Compared with the existing conventional calibration method of directly adjusting the PWM duty cycle up and down, it can greatly reduce the number of repeated adjustments, thereby further improving the calibration efficiency. In addition, it determines the light source brightness by obtaining the gray level value through the camera. Even under long-term and high-intensity calibration work, it is not easy to malfunction, reducing the problem of high failure rate of the calibration system caused by using a luminance meter for calibration under long-term and high-intensity work. Specific implementation mode

[0017] A method for calibrating the brightness of a light, comprising the following steps:

[0018] A. Test the brightness of the standard sample in the cold state and the hot state, and establish a first mapping relationship in one-to-one correspondence between the hot state brightness and the cold state brightness;

[0019] Based on the cold state brightness, hot state brightness, cold state PWM (pulse width modulation) duty cycle and hot state PWM duty cycle tested on the standard sample, establish a calculation model among them;

[0020] The brightness control module controls the standard sample to work according to different PWM duty cycles. In the cold state, use a luminance meter to test its brightness and use a camera to test the gray level value of its photo, and establish a second mapping relationship in one-to-one correspondence between the standard brightness and the standard gray level value based on this test data;

[0021] B. Set the initial PWM duty cycle. The brightness control module controls the light source to be calibrated to work according to the initial PWM duty cycle, and obtains the gray level value of the photo of the light source to be measured at this time through the camera;

[0022] C. Determine the standard brightness value according to the obtained gray level value according to the second mapping relationship; determine the hot state brightness value according to the standard brightness value according to the first mapping relationship; compare the hot state brightness value with the target hot state brightness value to judge whether its brightness deviation value is within the threshold range;

[0023] D. If the brightness deviation value is within the threshold range, the calibration is completed; if the brightness deviation value exceeds the threshold, calculate the theoretical hot state PWM duty cycle according to the calculation model established in step A, and the brightness control module controls the light source to be calibrated to work according to this theoretical hot state PWM duty cycle;

[0024] E. Obtain the gray level value of the photo of the light source to be measured at this time through the camera, determine the standard brightness value according to the obtained gray level value according to the second mapping relationship, determine the hot state brightness value according to the standard brightness value according to the first mapping relationship, and compare the hot state brightness value with the target hot state brightness value to judge whether its brightness deviation value is within the threshold range;

[0025] If it is within the threshold range, the calibration is completed; if it is not within the threshold range, the PWM duty cycle is finely adjusted in a way of up and down adjustment. If it is too large, it is increased; if it is too small, it is decreased. Then, the light source to be tested is controlled to work according to the adjusted PWM duty cycle, and step E is returned.

[0026] During the testing process of the standard sample, the brightness control module can determine the adjustment step of the PWM duty cycle according to the calibration accuracy requirements, and then measure the corresponding cold machine brightness and the gray scale value of the photo corresponding to the cold machine brightness, the hot machine brightness and the gray scale value of the photo corresponding to the hot machine brightness for each step. If the calibration accuracy requirement is 5%, the adjustment step of the PWM duty cycle can be set to 5%. The brightness is controlled at 100% PWM duty cycle, and each 5% PWM duty cycle is taken as one step, that is, the relevant brightness and gray scale value data are measured every 5% PWM. Usually, taking 5% as the adjustment step can meet the calibration accuracy requirements of most cases. If higher requirements for calibration accuracy are needed, the adjustment step can also be set to 2%, the brightness is controlled at 100% PWM duty cycle, and each 2% PWM duty cycle is taken as one step, that is, the relevant data are measured every 2% PWM.

[0027] The calculation models among the cold machine brightness, hot machine brightness, cold machine PWM duty cycle and hot machine PWM in step A are as follows:

[0028]

[0029] Where A, B, and C are constants; PWM (warm) is the PWM value measured in the hot machine test; Cd (warm) is the brightness value measured in the hot machine test; PWM (cold) is the PWM value measured in the cold machine test; Cd (cold) is the brightness value measured in the cold machine test; the values of A, B, and C can be obtained by substituting the cold machine brightness, hot machine brightness, cold machine PWM duty cycle and hot machine PWM duty cycle data measured in the standard sample test into the calculation model.

[0030] The threshold range of the brightness deviation value can be controlled within ±5%, which can meet the requirements of general usage scenarios.

[0031] In step F, the adjustment step of the PWM duty cycle can be 1% - 5%. Since in step F, the up and down adjustment of the PWM duty cycle is a fine adjustment, it is better to be consistent with the calibration accuracy.

Claims

1. A method for calibrating the brightness of a light, characterized in that, It includes the following steps: A. Test the brightness value of the standard sample in the cold state and the brightness value in the hot state, and establish a first mapping relationship in which the hot-state brightness value corresponds one-to-one with the cold-state brightness value; Based on the cold-state brightness value, hot-state brightness value, cold-state PWM (pulse width modulation) duty cycle ratio, and hot-state PWM duty cycle ratio tested on the standard sample, establish a calculation model among them; The brightness control module controls the standard sample to work at different PWM duty cycle ratios. In the cold state, use a brightness meter to measure its brightness and a camera to measure the gray scale value of its photo, and establish a second mapping relationship in which the cold-state brightness value corresponds one-to-one with the gray scale value based on this test data; B. Set the initial PWM duty cycle ratio. The brightness control module controls the light source to be calibrated to work according to the initial PWM duty cycle ratio, and obtains the gray scale value of the photo of the light source to be measured at this time through a camera; C. Determine the cold-state brightness value according to the gray scale value obtained and the second mapping relationship; determine the hot-state brightness value according to the cold-state brightness value and the first mapping relationship; compare the hot-state brightness value with the target hot-state brightness value to judge whether its brightness deviation value is within the threshold range; D. If the brightness deviation value is within the threshold range, the calibration is completed; if the brightness deviation value exceeds the threshold, calculate the theoretical hot-state PWM duty cycle ratio according to the calculation model established in step A, and the brightness control module controls the light source to be calibrated to work according to this theoretical hot-state PWM duty cycle ratio; E. Obtain the gray scale value of the photo of the light source to be measured at this time through a camera, determine the cold-state brightness value according to the gray scale value obtained and the second mapping relationship, determine the hot-state brightness value according to the cold-state brightness value and the first mapping relationship, and compare the hot-state brightness value with the target hot-state brightness value to judge whether its brightness deviation value is within the threshold range; F. If it is within the threshold range, the calibration is completed; if it is not within the threshold range, finely adjust the PWM duty cycle ratio in a way of up and down adjustment, increase it if it is too large and decrease it if it is too small, and then control the light source to be measured to work according to the adjusted PWM duty cycle ratio, and return to step E; The calculation model established among the cold-state brightness value, hot-state brightness value, cold-state PWM duty cycle ratio, and hot-state PWM duty cycle ratio tested on the standard sample in step A is as follows: A +B +C = 0, where A, B, and C are constants; PWM (warm) is the PWM duty ratio for the warm engine test; Cd (warm) is the warm engine brightness value for the warm engine test; PWM(cold) is the PWM duty cycle ratio tested in the cold state; Cd(cold) is the cold-state brightness value tested in the cold state; the values of A, B, and C are calculated by substituting the cold-state brightness value, hot-state brightness value, cold-state PWM duty cycle ratio, and hot-state PWM duty cycle ratio data tested on the standard sample into the calculation model.

2. The method for calibrating the brightness of a light according to claim 1, characterized in that The threshold range of the brightness deviation value is controlled within ±5%.

3. The method for calibrating the light brightness according to claim 1, wherein In step F, the adjustment step of the PWM duty cycle ratio is 1% - 5%.

4. The method for calibrating the light brightness according to claim 1, characterized in that, In step A, the brightness control module determines the adjustment step amplitude of the PWM duty cycle ratio according to the calibration accuracy, and measures the corresponding cold-state brightness value and the gray scale value of the photo corresponding to the cold-state brightness value, the hot-state brightness value and the gray scale value of the photo corresponding to the hot-state brightness value for each step.

5. The method for calibrating the light brightness according to claim 4, wherein The adjustment step amplitude of the PWM duty cycle ratio is 5%.

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