What Is the Calibration Technology of The LED Display Screen
The calibration of LED display box can greatly improve the display quality of the screen after splicing, and the relative field correction is more efficient, and it is not limited by time and site, and the cost is lower. Therefore, the cabinet correction technology will become an indispensable part in the manufacturing of LED display, with good prospects of application.
Because of the dispersion, attenuation of LED and discrete components of circuit components, the brightness and chromaticity of LED display are not consistent, and the quality of the display is seriously affected. In order to overcome the LED display brightness and chromaticity heterogeneity problem, point by point correction technology arises at the historic moment, and is developing rapidly, it can significantly improve the uniformity of LED display, to improve the display quality.
According to the different application situation, the point-by-point correction technology can be divided into two kinds: one is the box – box correction on the production line. The other is the large screen correction on site (field correction). In-situ correction technology can choose a good place to watch for correction, ensure the LED display screen in the field application environment to achieve satisfactory display effect, but the complex scene environment and long-distance technical support is limited field calibration problems. In particular, some foreign order field correction costs and difficulties are relatively large.
In order to ensure the uniformity of the factory LED screen and reduce the cost of technical support, the box body correction technology reflects its own unique value. The box calibration can greatly improve the display quality of the screen after splicing, and the relative field calibration is relatively efficient, and it is not limited by time and site, and the cost is lower. Therefore, the cabinet correction technology will become an indispensable part in the manufacturing of LED display, with good prospects of application.
First, the introduction of LED display box body correction
Case correction is a kind of production line correction, which requires LEDa screen manufacturers to increase the production line. Under normal circumstances, the housing correction is arranged in the factory before the last link, mainly used to eliminate the box of brightness and chromaticity difference between internal and enclosure, to improve the uniformity of LED display after joining together.
In addition to adding correction in the production process, manufacturers generally need to follow up the calibration effect of the screen. There are three common methods: first, all the boxes are stitched together to observe the effect of the display, but the amount of the stitching is larger and the implementation is not convenient. Secondly, some boxes were randomly selected to make a splice to observe the correction effect. Thirdly, the calibration effect of all the boxes is simulated by using the measurement data recorded by the calibration system.
The cabinet calibration needs to be carried out in the darkroom, and it needs to be equipped with the surface array imaging equipment and chromometer each to measure the brightness and chromaticity information of each box body. In order to ensure that all the calibration process of box body is under the influence of the external environment condition, to meet its goal of luminance and chrominance uniformity, dark room completely sealed, and the temperature and humidity as a constant value, in the process of calibration, and calibration of the instrument must be fixed enclosure, box must be placed above the base, avoid the influence of the ground reflection.
Are similar with the correction, in each case, the process of correction of the including data collection, data analysis, target setting, coefficient of correction coefficient calculation and upload, also need to control system.
Second, key technologies and difficulties
Housing correction is an effective way to improve the quality of LED display image, its key technology is mainly manifested in the following two aspects: one is the box body internal uniformity between pixels, 2 it is bright color degree of consistency between the box body.
1. The uniformity of pixels within the box
The internal pixel uniformity correction of the box body is similar to the field correction, which is more mature, including the light uniformity correction and bright dark line correction:
Uniformity correction :
(1) bright color degrees, by measuring equipment to measure the LED luminance and chrominance information of each LED bulb in the box, its measuring methods involving photometry and colorimetry and digital image processing related knowledge; The corresponding correction coefficient is calculated and sent to the receiver card of the corresponding box according to the corresponding calibration standard after the color information is obtained. After the box is lit, the display control system will adjust the LED’s current according to the calibration coefficient, so that all the leds in the box are in accordance with the brightness and chroma.
The brightness correction is to adjust the brightness of the fluctuating LED to the same level, and the maximum brightness value of most leds should be reduced appropriately during the adjustment of the brightness process. Color correction is based on the principle of the RGB color matching, by changing the RGB trichromatic color coordinate to solve the problem of color deviation, as shown in figure 3 for correction of before and after contrast figure color gamut, big triangle for correction before display color gamut, RGB trichromatic color coordinates discrete distribution; The small triangle is the color field of the corrected screen, and the RGB three color coordinate is better.
(2) due to mechanical machining accuracy and precision of assembly process, because of the limitation of splicing lamp plate spacing is slight inconsistent phenomenon, after the human visual system after low pass filtering process, the display will appear bright line or dark lines. Because of the existing mechanical process limitations, the small spacing display can significantly improve the homogeneity of the box.
2. The color uniformity between different boxes
Housing correction and in-situ correction has a remarkable differences, timing is not joining together in school is enclosure, timing the lack of the surrounding area as a reference in school, and after the correction need to ensure that case any stitching and there is no bright color degrees of difference. And, more importantly, as a band-pass filter, the human eye vision system to the brightness of the gentle gradient differences or the details of the minimal angular resolution is not sensitive, and for contains the edge of the steps in the low frequency signal is very sensitive. In the field of LED display screen, it is shown that the human eye can only distinguish the brightness difference between 4-5% of the LED pixels, but can easily identify the difference of the light color of 1% of the box body. In other words, the human eye has a low consistency requirement on the internal pixel of the box, and the consistency between the box body is higher. Therefore, the bright color consistency between the boxes is the key technology of the box body correction.
The color difference between the boxes is mainly reflected in two aspects:
(1) there is a difference between the average bright color of the box body. When the box is stitched together, there will be obvious boundary lines, which can be realized by adjusting the color field and setting the appropriate target value. When necessary, the colorimeter with higher precision shall be equipped for auxiliary measurement.
(2) the distribution of the bright color of the box is gradient gradient distribution, which is caused by the gradient distribution of the measurement data of the box. Since the visual system is not sensitive to the brightness difference of low frequency or smooth gradient, this problem is difficult to be found in single case correction. But when the box is spliced together, the brightness of the splicing will have a big jump, forming an obvious splicing line. This requires the calibration system to detect and solve the gradient distribution of the measured data.