DLP rear projector color wheel and color processing technology

1. The basic principle of DLP color wheel technology

As we all know, because DLP uses DMD micro-lens reflection technology, in the color processing, the single-chip and two-chip DMD methods use color wheels to complete the separation and processing of colors.

Generally speaking, the color wheel (COLOR WHEEL) is a combination of dichroic filters such as red, green, blue, and white. It can separate the transmitted white light and rotate it by a high-speed motor, and then separate them in order. Different monochromatic lights are on the designated light path, and finally they are synthesized by other optomechanical components to project a full-color image.

In terms of physical structure, the surface of the color wheel is a very thin metal layer. The metal layer uses vacuum film coating technology. The thickness of the coating corresponds to the spectral wavelengths of red, green, and blue. When white light passes through the metal coating layer, the The color corresponding to the spectral wavelength will pass through the color wheel, and other colors will be blocked and absorbed, thus completing the separation and filtering of the white light.

In a single-chip DMD projection system, the input signal is converted into RGB data, and the data is written into the SDRAM of the DMD in sequence. The white light source is focused on the color wheel through the focusing lens, and the light passing through the color wheel is then imaged on the surface of the DMD. When the color wheel rotates, red, green, and blue light sequentially hit the DMD. The color wheel and the video image are performed sequentially, so when the red light hits the DMD, the lens is tilted to "on" according to the position and intensity that the red information should display, and the green and blue light and the video signal work as well. The human visual system concentrates the red, green, and blue information and sees a full-color image. Through the projection lens, the image formed on the DMD surface can be projected onto a large screen.

In the two-chip DMD projection system, in order to improve the brightness and make up for the lack of red metal halide, the color wheel uses two auxiliary colors-magenta and yellow. Magenta fragments allow red and blue light to pass through, while yellow fragments can pass through red and green. The three-piece DMD uses a dichroic prism without the need for a dichroic wheel. Below we mainly discuss several color wheel technologies of single-chip DMD currently used in DLP rear projection units.

2. Several commonly used color wheel processing technologies and characteristics

Because the color wheel of a single-chip DMD projector can only process one color at a time, it will bring some loss of brightness. At the same time, due to the difference in the inherent characteristics of the spectral wavelength of different colors of light, colors will be produced Different from the restoration, the color of the picture often shows that red is not bright enough. Therefore, how to make the projector have sufficient display brightness and at the same time can fully guarantee the true reproduction of color is a key issue in the product design of each projector manufacturer, and one of the most important factors is color Design solutions for wheel technology.

The following are several commonly used DLP color wheel technologies:

The three-segment color wheel RGB is composed of three segments of red R, green G, and blue B. The products of different manufacturers have different designs for the opening angles of red, green, and blue. Generally speaking, the opening angle of red is larger. Can make up for the lack of red in the image. The prerequisite for using this color wheel technology is that the projector's optical machine part has relatively sufficient brightness, otherwise it may cause image brightness problems. At the same time, the color reproduction using the three-segment color wheel technology is relatively good. The four-segment color wheel RGBW is composed of four segments of red R, green G, blue B, and white W. The purpose of adding the white segment color is mainly to further increase the brightness of the projector. Generally, it can be increased by about 20% compared with the three-segment color wheel. But at the same time, this color wheel technology will also cause the problem of insufficient color reproduction of the projector, distorting the image color and reducing the image quality. In addition, in the design, the pulse signal can be synchronously locked in the W segment, and the pulse width corresponds to the width of the W segment, which can reduce the flicker of the picture to a certain extent. This technology is mainly used in conference rooms and teaching projectors. Six-segment color wheel Because DLP technology is more and more widely used in home theater projection and rear projection TVs with huge market potential, people have put forward higher requirements for DLP color reflection and the effect of playing continuous dynamic video pictures. The six-segment color wheel is a color wheel composed of six RGB RGB colors. With the corresponding increase in the speed of the color wheel (180HZ) and more pictures processed per unit time, this design effectively reduces moving images and rainbows on the edges. Effect, the dynamic effect of the video is better, and the color of the image is richer and more gorgeous. However, due to the more six-segment segmentation and more light loss when the light beam passes through each color segment, the brightness of the projector is often relatively low. Therefore, a few projector manufacturers have begun to design and adopt the 7-segment color wheel RGBRGBW technology To increase the brightness of the projector and reduce the flicker of the picture. This technology is mainly used for applications that require high household consumption and video. The gain-type color wheel SCRSCR (SequenTIal Color Recapture) is also called continuous color compensation technology. Its basic principle is similar to the above color wheel technology. The difference is that the color wheel surface uses Archimedes' principle spiral optical coating and light collecting column (light channel ) A special gain technology can compensate for part of the reflected light, so that the system brightness is greatly improved (about 40%). However, the processing technology of the color wheel is relatively complicated, and currently only a few projector manufacturers use it in products. From the technical development direction, this technology has great market potential.

The 4-segment color wheel is composed of RGBW (red, green, blue, and white). The purpose of adding the white segment is mainly to increase the brightness of the projector. The projectors using this color wheel technology are mostly products for business applications, which pay more attention to the image brightness performance.

The six-segment color wheel is a color wheel composed of 6 colors of RGBRGB (red, green, blue, red, green and blue). In our actual evaluation, this design can make the projected product have a significant improvement in color expression, especially There are obvious improvements in color levels. However, because the six-color segmentation is more separated, the light loss is also greater when the light-collecting column passes between the color segments, so the brightness of the projector is often relatively low. This technology is mainly used for applications that require high household consumption and video.

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