Discussion On Chroma Processing Technology Of LED Display Screen

All kinds of color processing technology:

1, the choice of primary color wavelength

LED display has a very wide application in all walks of life, and gezer wavelength of LED in the application of different places have different requirements, LED gezer wavelength selection for some of them are in order to obtain a good visual effect, some of them are in order to comply with the habits of people, and some is the industry standard, national standard, and even the rules of the international standard.

For example, the selection of green tube base color wavelength in the full color LED display; In the early days, we generally choose the wavelength of 570nm yellow-green LED, although the cost is low, but the display color gamut is small, color reduction is poor, brightness is low. After selecting the pure green tube with the wavelength of 525nm, the color gamut of the display screen is nearly doubled, and the color reduction degree is greatly improved, which greatly improves the visual effect of the display screen.

On the stock market display, for example, people usually use red for rising prices, green for falling prices and yellow for flat prices. In the transportation industry is strictly regulated by the national standards of the blue and green band for traffic, red band for prohibition. Therefore, the selection of primary color wavelength is one of the important links of LED display.

2, the allocation of white field color coordinates

White field coordinate allocation is one of the most basic technologies of full color LED display.

However, in the mid-1990s, due to the lack of industry standards and basic test means, usually only by human eyes, by feeling to determine the white field color coordinates, resulting in serious color bias and white field color temperature randomness. With the promulgations of industry standards and the completeness of testing methods, many manufacturers began to standardize the full color screen color matching process. However, due to the lack of theoretical guidance for color matching, some manufacturers often sacrifice the gray level of some primary colors to adjust the 100-field color coordinates, and the comprehensive performance can not be improved.

3, color uniformity processing

The color uniformity of LED display has always been a big problem for the industry. It is generally believed that the brightness uneven of LED can be corrected by single point to improve the brightness uniformity. The color inhomogeneity can not be corrected, can only be improved by subdividing and screening the LED color coordinates.

With the increasing requirements of LED display, only subdivision and screening of LED color coordinates can not meet people's critical eyes, comprehensive correction of the display to improve the uniformity of color is possible.

We found that even the same LED of the first brand in the world also has a large wavelength deviation and color saturation deviation, and the deviation range is much more than the threshold value of the human eye to green color difference. Therefore, it is of great significance to conduct color uniformity correction.

In the CIE1931 chrominance diagram, according to the law of the center of gravity, we find that: in the range of G (□Abcd) by mixing a certain proportion of red and blue, you can adjust the color coordinate of the mixed color to the intersection point O of cR and dB.

Although can make the color uniformity greatly improved. However, the corrected color saturation decreased significantly. At the same time, another premise of using red and blue to correct the uniformity of green chromatism is that the three LEDS of red, green and blue in the same pixel should be distributed centrally as far as possible to make the distance of red, green and blue color mix as close as possible, so as to achieve better results. Currently, the LED uniform distribution method usually adopted in the industry will bring confusion to the chromaticity uniformity correction.

In addition, the measurement of thousands of red, green and blue LED color coordinates is also a very difficult problem. We gave a hint.

4, color reduction processing

The birth of pure blue and pure green LED makes full color LED display popular in the industry with its wide color gamut and high brightness. However, the color coordinate of red, green and blue LED has a large deviation from that of PAL TV (see Table 1), resulting in poor color restoration of LED full color screen. Especially in the performance of human skin color, there is a more obvious visual bias.

Therefore, color reduction processing technology arises at the historic moment. Here the author recommends two methods of color reduction:

First, the color coordinate space transformation is carried out on the red, green and blue primary color LEDS, so that the color coordinate between LED and PAL TV is as close as possible, thus greatly improving the color restoration degree of LED display. However, this method greatly reduces the color gamut range of LED display, so that the color saturation of the screen is greatly reduced.

Second: correct only the most sensitive color gamut of skin color; Gamut that is not sensitive to other human eyes reduces the original color saturation as little as possible. In this way, a balance can be achieved between the degree of color reduction and color saturation.