Industrialization exploration of five primary color LED display

The status quo of the first and third primary color LED displays and further demand in the high-end market

LED display, from monochrome monochrome display in the early 1980s to double-primary multi-gray display (R+YG) in the late 1980s, to the three primary colors (R+G+B) in the mid-1990s People have been working hard to truly restore the colorfulness of nature. After long-term industrial development, in the near future, the three primary color LED display devices have performance in terms of brightness, wavelength, color purity, reduced light decay, and reduced failure rate. A substantial increase has entered the stage of maturity. Until now, LED display devices have always occupied the largest share of large-scale color development in indoor and outdoor areas, and this state will continue for many years. However, the recent international high-end application areas have further requirements for the existing display effects, especially the color gamut specification, which can not meet the detailed display requirements of some high-end fields. For example, high-end professional advertising, international conference HD screens, etc.; some national logos or company logos have high color value standards, and any visual deviation will cause dissent and even international contradictions.

Analyze the color gamut reproducibility of LED display devices, as shown in Figure 1: The color gamut of the three primary color LED display devices has reached 120% of the NTSC standard color gamut, however, in the CIE standard gamut, there are nearly 40% The area is outside the three primary color LED display area. How to further expand the range of display color gamut is an important exploration direction for us to meet high-end needs.

LED three primary color display compared to NTSC standard and sRGB color gamut

Figure 1: LED three primary color display and NTSC standard and sRGB color gamut comparison

Second, the color reproduction related sub-sector industry color gamut expansion solution:

As the market demands for color gamut reproduction continues to increase, new solutions and standards are constantly being developed in various fields to solve this problem.

a) LCD solution:

LCD display industry from the traditional CCFL backlight, to the emergence of RGB LED backlight in 2004, has been very popular until now; by 2006 LED laser backlight. In 2007, Sanyo-Epson first introduced four color display devices for mobile products, increasing the color gamut to more than 100% of the NTSC standard;

b) Solutions for the printing industry: from three-primary printing to four-primary printing, to six-color printing standards, and in recent years, more basic color printing standards are being introduced.

c) The standard for color reproduction has been extended in the color gamut. It has been introduced: NTSC 1953 standard, sRGB standard, Adobe RGB standard, Adobe Wide Gamut RGB standard, etc. These standards are based on the basis of three primary colors.

Three primary colors show the standard of each stage

Figure 2: Three primary colors show the criteria for each stage

Third, the LED display in the extended color gamut scheme selection and feasibility demonstration:

According to the theory of colorimetry, there are several ways to solve the problem of "existing the expansion of the existing three primary colors".

a) The first solution: to improve the color purity of each color of the three primary colors, however, the LED materials produced by the conventional process, each color has a similar component of the stray wavelength, so that the direction of this effort is always inconclusive. To improve the color purity of LED devices, only LED lasers can be done. As shown in Figure 3, the color gamut can reach more than 150% of the NTSC standard, and the effect is better; however, this method is almost impossible to use in mass production.

Color gamut of laser LED devices

Figure 3: Color gamut of laser LED devices

b) The second scheme: increase the number of primary colors, select the LED luminescent materials that are mass-produced at the current stage, we choose cyan (C: 505nm) and yellow (Y: 580nm) to form RGCB four primary colors or RYGB four primary colors. Or the RYGCB five primary color pixel combination, as shown in Figure 4, the five primary colors gamut can reach more than 200% of the NTSC standard. The experiment also fully proved that the displayed color gamut has a significant improvement.

MYGCB five-primary LED display gamut

Figure 4: Color gamut of the RYGCB five-primary LED display

c) along the idea of ​​the second scheme, continue to increase the number of primary colors, the problem arises, first of all, the proportion of cost increase is not proportional to the improvement of the effect, followed by the maturity of mass production of LED materials of other wavelengths;

In summary, the best way to extend the color gamut is the RYGCB five-primary color display. The comparison results are shown in Table 1.

Table 1 LED display color gamut expansion scheme comparison table

Serial number Solution advantage Disadvantage Comprehensive conclusion
1 Increase the color purity of the three primary colors RGB There are no theoretical obstacles to using the existing three primary color standards.

The gamut is increased less;

High color purity LED luminescent materials are difficult to achieve.

Secondary election
2 Increase the yellow base color with RGBY four primary colors LED luminescent materials are available in mass production specifications.

The gamut is increased less;

The theoretical and equipment standards have changed considerably.

Good choice
3 Increase the base color - cyan, use RGCB four primary colors. LED luminescent materials are available in mass production specifications.

The gamut is increased less;

The theoretical and equipment standards have changed considerably.

Good choice
4 Add yellow base color and cyan base color, use RYGCB five primary colors.

The gamut is increased;

LED luminescent materials are available in mass production specifications.

higher cost;

The theory and equipment standards have changed a lot.

Most preferred
5 Use a display scheme of more than six primary colors. The gamut is increased.

The cost is too high;

The theory and equipment standards have changed a lot.

Secondary election

Discussion on industrialization of four- and five-primary LED display systems

1) Sub-process industrialization:

The application of the complete LED display video system is as follows, divided into front and back sections. The front section is a general-purpose video device, and the latter section is a dedicated device for LED display.

Table 2: The front part of the video system:

Video system front device

Table 3: Video system back-end equipment:

Video system backend device

The theoretical analysis of the five primary color LED display is no problem, and the industrialization needs to be carried out in two stages;

The first stage is based on the premise that the current video front-end equipment and interface standards are unchanged, that is, the current three-primary color standard, only the rear-end equipment of the LED display is completely entered into the display standard of the five primary colors; this is also the second The basis of the stage.

In the second phase, from the beginning of the formation of the video source to the final display, the standards of all devices and interfaces enter the five-primary standard.

In the first stage, the input of the latter device is still the signal of the three primary colors, so the work of chroma space conversion in the video processor is the key theory of this design, which is rather cumbersome and will be elaborated in another article. .

2) Problems in the process of industrialization:

a) The first stage of chromaticity space conversion, because the result of the operation is not unique, it is easy to cause color distortion, and it needs constant experimental correction to form a correct mathematical operation model.

b) At the beginning, because the display part has increased LED devices and drivers of two wavelengths, the overall cost is significantly improved, so only high-end applications and high-end consumer markets can be considered.

c) Because of the increase in the number of devices, the design difficulty of small-pitch display screens is further increased.

V. Conclusion

Chroma processing technology throughout the history of the development of the LED display, is one of the core technology LED display this comprehensive discipline in. The LED display technology based on five primary colors is more in line with human high-end requirements for display devices, and is an important development direction for LED display in the future. Both theory and experiment have fully proved that it is feasible to enter the industrialization of LED display technology based on five primary colors.

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