Application and advantages of box calibration tech

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Application and advantages of LED full-color display box correction technology

. Therefore, the box calibration technology will become an indispensable part of the LED display manufacturing process, and has a good application prospect

due to the discreteness and attenuation of LED light-emitting tubes and the discreteness of circuit components, LED display screen has inconsistent brightness and chromaticity, which seriously affects the display quality. In order to overcome the non-uniformity of LED display brightness and chromaticity, point by point correction technology came into being and developed rapidly. It can significantly improve the uniformity of LED display and improve the display quality

according to different application occasions, point by point calibration 1. The utilization range technology of metal tensile testing machine can be divided into two types: one is box by box calibration on the production line (box calibration); The other is field large screen correction (field correction). The field calibration technology can select a suitable viewing place for calibration to ensure that the LED display screen can achieve a satisfactory display effect in the field application environment. However, the complex and changeable field environment and remote technical support are the difficulties that limit the field calibration. In particular, the cost and difficulty of on-site correction of some foreign orders are relatively large

in order to ensure the uniformity of the factory LED screen and reduce the cost of technical support, the box calibration technology reflects its unique value. The box correction can greatly improve the display quality of the display screen after splicing, and is more efficient than the field correction, not limited by time and site, and the cost is lower. Therefore, the box calibration technology will become an indispensable part of the LED display manufacturing process, and has a good application prospect

I. Introduction to LED display box calibration

box calibration is a kind of production line calibration, which requires LED display manufacturers to add this link to the production line. Generally, the box calibration is the last link arranged before leaving the factory, which is mainly used to eliminate the brightness and chromaticity differences inside the box and between the boxes, and improve the uniformity of the LED display after splicing

in addition to adding a calibration link in the production process, manufacturers generally need to follow up the calibration effect of the screen. There are three common methods: first, all boxes are spliced to observe the display effect, but the splicing workload is relatively large, which is inconvenient to realize; Second, randomly select some boxes for splicing and observe the correction effect; The third is to use the measured data recorded by the calibration system to simulate and evaluate the calibration effect of all boxes. The schematic diagram of LED production line with box calibration and simulation evaluation/sampling inspection links is shown in Figure 1

box calibration needs to be carried out in a dark room. One area array imaging device and one colorimeter are required to measure the brightness and chromaticity information of each box. In order to ensure that the calibration process of all boxes is not affected by external environmental conditions and achieve the goal of brightness and chromaticity consistency, the darkroom is required to be completely sealed, and the temperature and humidity are constant. During the calibration process, the position of the box and the calibration instrument must be fixed, and the box must be placed on the base to avoid the impact of ground reflection

similar to field correction, for each box, the process of box correction includes data acquisition, data analysis, target value setting, correction coefficient calculation and coefficient uploading, and also requires the cooperation of the control system

II. Key technologies and difficulties

box correction is an effective way to improve the image quality of LED display screen. Its key technologies are mainly reflected in the following two aspects: one is the uniformity of pixels inside the box, and the other is the consistency of brightness between boxes

1. Uniformity between pixels inside the box

the uniformity correction between pixels inside the box is basically similar to the field correction, which is relatively mature, including brightness uniformity correction and light dark line correction:

(1) brightness uniformity correction establishes the brightness and chromaticity information of engineering plastic recycling, modification and high value-added utilization system lamps by measuring each LED in the LED box through measuring equipment. The measurement method involves photometry Knowledge of colorimetry and digital image processing; After obtaining the chromaticity information of light by light, the corresponding correction coefficient is calculated according to the corresponding correction standard and sent to the receiving card of the corresponding box; After the box is lit, the display control system will adjust the LED current according to the correction coefficient to make the brightness and chromaticity of all LEDs in the box consistent

the brightness correction of hot-rolled ribbed steel bars for reinforced concrete GB 1499 ⑴ 998 is to adjust the brightness of fluctuating led to the same level. In the process of brightness adjustment, it is necessary to appropriately reduce the maximum brightness value of most LEDs. Chromaticity calibration is to solve the problem of chromaticity deviation by changing the color coordinates of RGB three colors according to the RGB color matching principle. Figure 3 shows the color gamut comparison before and after correction, the large triangle is the color gamut of the display screen before correction, and the color coordinates of RGB three colors are distributed discretely; The small triangle is the corrected color gamut of the display screen, and the RGB three color coordinates have good consistency

(2) due to the limitations of machining accuracy, assembly accuracy and other process reasons, there is a slight inconsistency in the spacing of the splicing lamp plates. After the low-pass filtering process of the human visual system, bright or dark lines will appear in the display. Due to the limitations of the existing mechanical process, the small spacing display screen generally requires that the uniformity of the box body can be significantly improved only after the bright and dark lines are corrected

2. Consistency of brightness and chromaticity between different boxes

there is a significant difference between box correction and field correction, that is, the box is not spliced during correction, and the surrounding area is not used as a reference during correction. After correction, it is necessary to ensure that the box is spliced arbitrarily without brightness and chromaticity difference. More importantly, as a band-pass filter, the human visual system is not sensitive to the gradual brightness difference or the small detail difference of angular resolution, but is extremely sensitive to the edge step signal with medium and low frequency components. When applied to the field of LED display, the human eye can only distinguish more than% of the brightness difference between LED pixels, but can easily identify 1% of the box brightness difference. In other words, the human eye has lower requirements for the consistency of pixels inside the box, but higher requirements for the consistency between boxes. Therefore, the consistency of brightness and color between boxes is the unique key technology of box correction

the inconsistency of brightness and chromaticity between boxes is mainly reflected in two aspects:

(1) there are differences in the average brightness and chromaticity between boxes. When boxes are spliced, obvious boundary lines will appear, which can be achieved by adjusting the color gamut and setting appropriate target values; If necessary, a colorimeter with higher accuracy shall be equipped for auxiliary measurement

(2) the brightness distribution of the box presents a gradient distribution, which is caused by the gradient distribution of the measured data of the box. Since the visual system is not sensitive to the brightness difference of low frequency, i.e. smooth gradient, this problem is difficult to be found in single box calibration. However, when the value of box splicing is as high as 1.9 billion yuan, the brightness of splicing will jump greatly, forming an obvious splicing line. This requires that the calibration system can detect and solve the gradient distribution problem of the measured data

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