At present, LED full-color display screens are in the factory situation, and the cost is not cheap. Although the theoretical life span is 100,000 hours, in fact, the uniformity will deteriorate after running for about 5,000 to 10,000 hours, and it will start to become flowery and the commercial value will decrease. After 15,000 to 20,000 hours, the commercial value is almost lost, causing a huge waste of social resources.
Therefore, whether it is before leaving the factory or after a period of use, the point-by-point correction technology allows users to greatly improve the uniformity of the display screen in a very short time and at a very low cost, and significantly improve the image quality. Before being applied to the factory, point-by-point correction is a quality improvement method, which means an increase in competitiveness and an expansion of profit margins; after being used for a period of time, point-by-point correction can prolong the display effect of the full-color LED display for users. Create more commercial value and reduce waste of resources.
There are currently two mainstream point-by-point correction techniques:
1. On-site calibration point by point
It is to operate the entire large screen that should be installed. Due to the impact of the environment, weather and technical compatibility issues in different places, the calibration cost is high, especially for the maintenance of some foreign orders.
2. Point-by-point calibration of the LED cabinet
It can greatly improve the consistency of the display screen, and it is uniformly calibrated in the production workshop, so the cost is relatively low, and the correction effect is better.
At present, LED display manufacturers use box-by-point calibration, which is a testing procedure that must be passed before the LED transparent screen leaves the factory. Witham box calibration technology is at the forefront of the industry, and the transparent screen is highly adaptable to various environments. The display effect is consistent.
The following focuses on the point-by-point calibration of the cabinet:
The cabinet calibration is the last link arranged before leaving the factory. It is mainly used to eliminate the difference in brightness and chromaticity between the inside of the cabinet and the cabinet, and to improve the uniformity of the LED display after splicing.
In addition to adding calibration links in the production process, manufacturers generally need to follow up on the calibration effects of the screens when they leave the factory. There are three commonly used methods: one is to splice all the cabinets together to observe the display effect, but the work load of the splicing is relatively large, which is inconvenient to realize; the second is to randomly select part of the cabinets for splicing to observe the correction effect; three It uses the measurement data recorded by the calibration system to simulate and evaluate the calibration effects of all cabinets. The LED production line for cabinet calibration and simulation evaluation/sampling inspection has been added.
Similar to on-site calibration, for each cabinet, the cabinet calibration process includes data collection, data analysis, target value setting, correction coefficient calculation and coefficient upload, and also requires the cooperation of the control system.
Key technologies and difficulties:
Cabinet correction is an effective way to improve the image quality of LED transparent screens. Its key technical aspects are mainly reflected in the following two aspects:
1. Uniformity between pixels inside the cabinet
Including light and chromaticity uniformity correction and light and dark line correction:
Brightness and chromaticity uniformity correction:
Measure the brightness and chromaticity information of each LED lamp in the LED cabinet by measuring equipment. The measurement method involves knowledge of photometry, chromaticity and digital image processing; after obtaining the point-by-point brightness and chromaticity information, it will be based on the corresponding calibration standards. , Calculate the corresponding correction coefficient and send it 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, so that the brightness and chromaticity of all the LEDs in the box are consistent.
Bright and dark line correction:
It is to adjust the brightness of the fluctuating LED to a consistent level. In the process of adjusting the brightness, it is necessary to appropriately reduce the maximum brightness value of most of the LEDs. Chromaticity correction is based on the principle of RGB color matching. The problem of chromaticity deviation is solved by changing the color coordinates of the RGB three colors. It is the color gamut comparison chart before and after correction. The big triangle is the color gamut of the display before correction. RGB three colors The color coordinates are discretely distributed; the small triangles are the corrected color gamut of the display screen, and the RGB three-color color coordinates are consistent.
(2) Due to the limitation of machining precision, assembly precision and other technological reasons, there is a slight inconsistency in the spacing of the spliced lamp panels, and bright or dark lines will appear during display.
2. Brightness and chromaticity consistency between cabinets
The human eye can only distinguish the brightness difference of more than 4-5% between the LED pixels, but it can easily recognize the 1% difference in the brightness and chromaticity of the cabinet. That is to say, the human eye has low requirements for the consistency of the pixels inside the cabinets, but higher requirements for the consistency between the cabinets. Therefore, the consistency of brightness and chromaticity between cabinets is a unique key technology for cabinet calibration.
The inconsistency of brightness and chromaticity between cabinets is mainly reflected in two aspects:
(1) There are differences in the average brightness and chromaticity between the cabinets. When the cabinets are spliced, there will be obvious boundary lines. This can be achieved by adjusting the color gamut and setting appropriate target values; when necessary, precision is required A higher colorimeter is used to perform auxiliary measurements.
(2) The brightness and chromaticity distribution of the cabinet presents a gradient distribution, which is caused by the phenomenon of gradient distribution in the measurement data of the cabinet. When the cabinets are spliced together, the brightness of the splicing place will undergo a large jump, forming an obvious splicing line. This requires the calibration system to be able to detect and solve the problem of gradient distribution of the measured data.
