Briefly talk about various color processing technologies of LED display

Although the LEDs are monochromatic, the LEDs of each color still have a half-wave width of about 30 to 50 nm, so the color saturation is limited.

One, 3+2 multi-primary color processing method:

In recent years, in the field of flat panel display, I am keen to discuss 3+3 multi-primary color display (red, green, blue, yellow, blue, purple) to expand the color gamut and reproduce more abundant natural colors. So, can the LED display achieve 3+3 multi-primary display?

We know that in the visible range, yellow and blue are monochromatic, and we have high-yellow yellow and cyan LEDs. The purple color is the complex color, and the single-chip purple LED does not exist. Although we can not achieve red, green, blue plus yellow, blue, purple 3 + 3 multi-color led display. However, it is feasible to study red, green, blue, yellow, and blue 3+2 multi-color LED display screens. Because of the large number of high-saturation yellows and cyan in nature, the study has some value.

In the current various TV standards, the video source has only three primary colors of red, green and blue, and no yellow or blue. Then, how to display the terminal yellow and blue primary colors?

In fact, when determining the driving strength of the primary colors of yellow and cyan; we follow the following three principles:

1. While increasing the color saturation, the color tone must not be changed;

2. The purpose of increasing the primary colors of yellow and cyan is to enlarge the color gamut and thus increase the color saturation. The overall brightness value cannot be changed;

3. Take D65 as the center; take the RYGCB color gamut boundary as the end point, and linearly expand the points in the gamut.

Under the guidance of the above three principles; according to the gravity center law, we can find 3+2 multi-primary chromaticity processing methods. However, in order to truly realize the 3+2 multi-primary full-color screen, we have to overcome the difficulties of insufficient brightness of yellow and cyan LEDs;

Second, color reproduction processing:

The birth of pure blue and pure green LEDs has made the full-color LED display popular in the industry for its wide color gamut and high brightness. However, due to the large deviation between the chromaticity coordinates of the red, green and blue LEDs and the chromaticity coordinates of the PAL TV red, green and blue (see Table 1), the color reproduction of the LED full color screen is poor. Especially when expressing the skin color of a person, there is a visually significant deviation. As a result, color reproduction processing technology came into being. Here I recommend two methods of color reproduction:

1. Perform color coordinate transformation on the red, green and blue primary color LEDs, so that the three primary color coordinates between the LED and the PAL television are as close as possible, thereby greatly improving the color reproduction degree of the LED display. However, this method greatly reduces the color gamut range of the led display, and the color saturation of the picture is greatly reduced.

2. Correctly correct only the skin color gamut that is most sensitive to the human eye; and the color gamut that is not sensitive enough to other people's eyes to reduce the original color saturation as much as possible. This is done to achieve a balance between color reproduction and color saturation.

Third, the choice of the primary color wavelength:

Led display screens are getting higher and higher with people's requirements for LED display screens. Only subdividing and screening LED color coordinates can not satisfy people's critical eye, and comprehensive correction processing is performed on the display screen to make chromaticity uniformity. Improvements are achievable.

We found that even the same brand of the international first brand LED has large wavelength deviation and color saturation deviation, and the deviation range greatly exceeds the human eye's threshold for green color difference identification. Therefore, it is important to perform chromaticity uniformity correction. meaningful.

In the CIE1931 chromaticity diagram, according to the law of gravity center, we found that any point in the G range (â–¡abcd) can be mixed with a certain proportion of red and blue, and the color coordinates of the mixed color can be adjusted to the straight line cR and The intersection of the straight line dB.

Although the chromaticity uniformity can be greatly improved. However, the corrected color saturation is significantly reduced. At the same time, another premise of using red and blue to correct the uniformity of green chromaticity is that the red, green and blue LEDs in the same pixel should be concentrated as much as possible so that the red, green and blue color mixing distances are as close as possible to achieve better. Effect. At present, the LED uniform distribution method is usually used in the industry to bring confusion to the chromaticity uniformity correction. In addition, how to measure the tens of thousands of red, green and blue LED color coordinates is also a very difficult problem. We gave a hint for this.

Fourth, chroma uniformity processing:

The problem of uniformity of chromaticity of led display has always been a big problem for people in the industry. It is generally believed that the brightness of LEDs is not uniform and can be corrected by single point to improve brightness uniformity. The chromaticity unevenness cannot be corrected, and can only be improved by subdividing and filtering the LED color coordinates.

Fifth, the allocation of white field color coordinates:

White field color coordinate modulation is one of the most basic technologies for full color LED display. However, in the mid-1990s, due to the lack of industry standards and basic testing methods, the white-field color coordinates were usually determined by the human eye and by feeling, resulting in random color cast and white-field color temperature. With the promulgation of industry standards and the complete testing methods, many manufacturers have begun to regulate the full color screen color matching process. However, some manufacturers still use the theoretical guidance of lack of color matching, often at the expense of the gray level of some primary colors to match the hundred field color coordinates, the overall performance is not improved.

In summary, we mainly discuss three aspects:

1, how to improve the uniformity of the color of the led display;

2. How to expand the color gamut and restore more natural colors;

3. How to improve the color reproduction degree of the led display;

The above-mentioned various color processing techniques are interrelated in the specific implementation, and some aspects are not even compatible with fish and bear's paw. The integrated LED display screen also needs to perform brightness uniformity correction, gray scale nonlinear transformation, noise reduction processing, image enhancement processing, dynamic pixel processing, etc., and the whole signal processing flow is very complicated. Therefore, we must comprehensively weigh the performance from the perspective of the system, grasp the order of each treatment, and increase the depth of signal processing, in order to make the LED full-color display show a colorful, colorful and wonderful world.

There are a wide range of applications in various industries, and there are different requirements for the primary wavelength of LEDs in different applications. The choice of LED primary wavelength is to achieve good visual effects, some to meet people's habits, and some to It is also the regulation of industry standards, national standards and even international standards.

For example, the choice of the wavelength of the green tube in the full-color LED display; in the early days, the yellow-green LED with a wavelength of 570 nm was generally used. Although the cost is low, the color gamut of the display is small, the color reproduction is poor, and the brightness is low. After selecting a pure green tube with a wavelength of 525nm, the color gamut of the display has nearly doubled, and the color reproduction degree has been greatly improved, which greatly improves the visual effect of the display. For example, in the securities market display screen, people are usually accustomed to using red to indicate that the stock price has risen, green to indicate that the stock price has fallen, and to use yellow to indicate the flat. In the transportation industry, the blue-green band is strictly defined by the national standard, and the red band is prohibited. Therefore, the choice of the primary color wavelength is one of the important links of the LED display.

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