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Color video display for projection systems. US 7,920,214

[Category : - Audio - Video]
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The means of formation of a color video display for projection systems with one cathode-ray tube (United States Patent 7,920,214)

The invention refers to the means of formation of a color video display for projection systems, providing the projection of an enlarged TV or computer image on a reflective or refractive screen of big sizes, and it can be used in projecting video-projectors, video-monitors, multimedia projectors, 3D projectors, projecting TV-sets.
The means of forming a video image with three-monochrome cathode-ray tube (CRT) with the basic colors red (R), green (G) and blue (B) is widely known. In this means of reflecting the basic colors (R, G, B), formed on separate CRTs with the help of projecting objective-lenses and catadioptric optics, are projected on the full screen where the combination takes place and the color display appears.
In the patent RU ? 2082206 the means is described where the images of three CRTs are preliminarily combined with the help of prism cube and dichroic (color-separating) mirrors, and then project on the screen.
A number of characteristic drawbacks are peculiar to the wide- known means of three CRTs:
1. While projecting the three spatially distributed images on the main screen difficult-to-remove trapezoid distortion appear.
2. Dissimilar changes in CRTs characteristics in the course of time (dissimilar senility) leads to the smear of the image.
3. The devices that use these three CRT have overall dimensions and mass.
4. The regulation of the image combination is realized mechanically.

The offered invention essentially differs from the others: the display of the three basic colors (R, G, B) are quartered on the screen by one one-ray projection tube of a special construction (pic. 1). The screen of such tube is divided into three rectangular spheres for red (R), green (G) and blue (B) images and each sphere is covered by the corresponding phosphor. The sizes of the spheres are chosen depending on the necessary correlation of the sizes of the frame (5:3 16:9, etc.). The further explanation of the invention will be given by an example of the video-projecting device functioning, the enlarged block-sketch of which is given on the pic. 2. The device consists of the following main knots: 1. The micro- processor device processing the video-signal. 2. The control unit of CRT. 3. The declining theory. 4. CRT. 5. Dichroic mirror (or prism) system of combining images: (r)- common reflecting mirror; (g) and (b)- dichroic mirrors. (L1), (L2), (L3)- short-focal-length lenses. 6. Projecting objective-lenses. 7. The screen. 8. Program control unit.
The device functions as follows: the video-signal enters the micro-processor device processing the video-signal (1), where it quantizes and undergoes program processing with the aim of dividing the image into three components (of the frame) of basic colors (R, G, B). The essence of the program processing is shown on the pic.3. The device (1) provides for receiving the corresponding frame (FSS) and line synchronization signals (LSS), which go to the control (2) unit of CRT. The processed video-signal enters into CRT. Thus the corresponding dot matrix is formed on the CRT screen; that is the information of the red (R) frame exposes the red phosphor of CRT, the information of the green (G) frame exposes the green phosphor and the information of the blue (B) frame exposes the blue phosphor. In this way on the CRT screen three images of basic colors are formed. Opposite the CRT screen three short- focal-length rectangular lenses (L1), (L2), (L3) are located (according to the sizes of R. G, B images), they are situated parallel to the surface of CRT in such a distance that the images of the basic colors (R, G, B) were situated on the focal plane of the lenses. Lenses are meant for focusing the image of basic colors in the infinite distance, and that provides for getting further color display in one plain. Further the dichroic mirror (or prism) system for combining images (5) is located. The device (5) consists of three mirrors- one reflecting (r) and two dichroic (g, b). The mirrors are inclined towards the surface of the tube for 45 degrees; they are parallel and have a common optic axis. The mirror (r) reflects the red frame, the mirror (g) lets through the red frame and reflects the green, and the mirror (b) lets through the red and green frames and reflects the blue. In this way three monochromic images of the basic colors are combined and one color image is formed, with help of projecting object-glass (6) it is projected on the screen (7).
Let?s note that the succession of the colors (R, G, B) on the CRT screen is conditional and any other succession is possible (B, R, G; G, R, B etc.).
The program control unit (8) is meant for shifting separate images (R, G, B) within small limits with the aim of their exact combination and final set-up. It also serves for the program controlling by the other characteristics of the video-signal (brightness, contrast, saturation, etc.).
The given invention allows to get rid of the following drawbacks of the existing analogues:
1. The three images of the basic colors are easily combined and their final combination is realized not by mechanical regulation but with the help of program control.
2. Changes in CRTs characteristics in the course of time (senility) happen in the same way for all the colors, as only one tube is used and the set-up system doesn?t shatter.
3. Small overall dimensions and weight (compactness), as only one tube is used.
4. The given method fits better for the realization of high definition TV projection (HDTV), as the ideal and stable combination of the three basic color images combination is possible.
The invention can be realized taking into account today?s level of technologies, as for its realization old-established components are used: CRT made according to the technology of monochromic projecting tubes; dichroic mirrors and prisms; projective object-glass, etc. The program processing of the video-signal in the real time with triple speed doesn?t make difficulties for modern micro-processors.

Appendix:
Pic. 1- The image of the cathode-ray tube.
Pic. 2- The block-sketch of the video- projection device.
Pic. 3- The graphical representation of the essence of the video-signal procession on the example of a frame.


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