EA008119B1 - Method of forming colored video image for projection systems with one cathode ray tube - Google Patents

Abstract

The invention relates to methods of forming video image for projection systems, providing projection of increased TV or PC image onto a big-sized reflective or transparent screen and can be used in designing video projectors, video monitors, multi-media projectors, 3 D projectors, projection TV sets.A well-known prior art method of video image forming with three monochrome cathode ray tubes (CLT) of main colors – red (R), green (G) and blue (B) lights. According to said method images of main colors (R,G,B) formed on separate CLT using projection lenses and catadioptric optical system are projected upon a common screen, where the lights are converged and a color image is produced.The proposed invention differs greatly from existing methods.The images of three main colors are displayed on a screen of a specially-designed (4) single-beam projection tube. The screen of such tube is separated into three rectangular areas for (R), green (G) and blue (B) images and each area is coated with corresponding phosphor. Size of the areas is selected depending upon the required ratio of a frame size. First a video signal is digitized and subjected to a program processing. The processing is aimed at separating a colored frame into three constituents of red, green and blue lights. The resulted three frames are displayed on the tube screen. Thus, three monochrome (R,G,B) image constituents of one colored frame are formed on a screen. Opposite the CLT screen there arranged short-focus rectangular lenses (L1;L2;L3) (lenses sizes correspond to the R,G,B image sizes). The lenses are arranged parallel to the R,G,B surface at such distance that the R,G,B images are to be in the lens focal plane. The lenses are assigned for focusing the R,G,B images into infinity, thus providing further displaying of colored image in one plane. Further is located a dichroic mirror (or prism) system of image convergence (5) by means of which three monochrome R,G,B images are converged and one colored image is formed which is projected on a screen (7) through a projection lens (6).The proposed invention provides getting rid of drawbacks existing in analogues, namely:1. Three main R,G,B color images are easily converged and their final convergence is program controlled.2. The CLT feature changes (aging) occur equally for all colors, since only one tube is used and tuned system remained tuned.3. Small dimensions and weight (compactness) due to the use of one tube.4. The present invention is more suitable for using a high-definition projection TV (HDTV) which provides ideal and stable convergence of three main R,G,B colors images.

Description

The invention relates to methods for generating a video for projection systems that provide a projection of an enlarged television or computer image on a reflective or translucent screen of large size, and can be used in the design of video projectors, video monitors, multimedia projectors, 3Ό projectors, projection TVs.

A well-known method of forming a video image with three monochrome cathode-ray tubes (CRT) of the primary colors of red (I), green (O) and blue (B). In this method, the primary colors (I, O, B), formed on separate CRTs using projection lenses and mirror-lens optics, are projected onto a common screen, where they are combined and a color image is obtained.

Patent Yay 2082206 describes a method in which images from three CRTs are previously combined with a prism-cube and dichroic (color separation) mirrors, and then projected onto the screen. All known methods on three CRTs have a number of characteristic drawbacks.

1. When projecting onto a common screen of three spatially separated images, there are difficult to remove trapezoidal distortion.

2. An unequal change in the characteristics of a CRT over time (unequal aging) leads to a blurred image.

3. Devices using three CRTs have large dimensions and mass (bulky).

4. Image alignment adjustment is done mechanically.

The proposed invention differs significantly from the existing ones: the images of the three primary colors (I, O, B) are placed on the screen of one single-beam projection tube of a special design (Fig. 1). The screen of such a tube is divided into three rectangular areas for red (I), green (O) and blue (B) images, and each area is covered with a corresponding phosphor. The sizes of the areas are selected depending on the required aspect ratio of the frame (5: 3, 16: 9, etc.). A further explanation of the invention will be given by the example of the functioning of a video projection device, the enlarged block diagram of which is shown in FIG. 2. The device consists of the following main components: 1 - microprocessor-based video signal processing device, 2 - CRT control unit, 3 - deflecting system, 4 - CRT, 5 - dichroic mirror (or prism) image registration system: (d) - conventional reflecting mirror ; (e) and (b) - dichroic mirrors; (B1), (b2), (b3) - short-focus lenses, 6 - projection lens, 7 - screen, 8 - program control unit.

The device operates as follows.

The video signal enters the microprocessor-based video signal processing device (1), in which it is digitized and subjected to software processing in order to divide the image into three components (frame) of primary colors (I, O, B). The essence of software processing is shown in FIG. 3. The device (1) also provides for obtaining the appropriate personnel (XI) and lowercase (FID) clock pulses, which are fed to the CRT control unit (2). The processed video signal is fed to the CRT. Thus, the corresponding raster is formed on the screen of a CRT, i.e. the information of the red (I) frame illuminates the red phosphor of the CRT, the green (O) frame - the green phosphor, and the blue (B) frame the blue phosphor. Thus, three images of primary colors are formed on the CRT screen. Opposite the CRT screen there are three short-focus rectangular (according to image sizes I, O, B) lenses (B1), (B2), (B3), they are arranged parallel to the surface of the CRT at such a distance that the images of the primary colors (I, O , B) were in the focal plane of the lenses. The lenses are designed to focus the images of primary colors to infinity, which ensures further color image in one plane. Next is the dichroic mirror (or prism) image registration system (5). The device (5) consists of three mirrors, one reflecting (d) and two dichroic (d, b). The mirrors are inclined with respect to the tube surface by 45 °, parallel with each other and have a common optical axis. The mirror (d) reflects the red frame, the mirror (e) skips the red frame and reflects the green, and the mirror (b) skips the red and green frames and reflects the blue. Thus, three monochrome images of primary colors are combined and a single color image is formed, which is projected onto the screen (7) using a projection lens (6). Note that the sequence of colors (I, O, B) on the screen of a CRT is arbitrary and any other sequence (B, I, O; O, I, B, etc.) is possible. The program control block (8) is designed to move individual images (I, O, B) within a small range in order to precisely align them and final settings, and also serves for programmatically controlling other video signal characteristics (brightness, contrast, saturation, etc. .).

This invention allows to get rid of all the above disadvantages of existing analogues, namely:

1) three images of primary colors are easily combined, and their final combination is made not by mechanical adjustment, but by means of program control;

2) the change in the characteristics of a CRT with time (aging) for all colors is the same, since one tube is used and the tuned system is not upset;

3) small dimensions and weight (compactness), since one tube is used;

4) this method is more suitable for the implementation of high-definition projection TV

- 1 008119 (NETU), because ideal and stable combination of three images of primary colors is possible.

The invention is feasible with the current level of technology, since its implementation uses long-used components: CRT, manufactured according to the technology of monochrome projection tubes; dichroic mirrors or prisms; projection lens, etc. A software processing of the video signal in real time with a threefold speed is not difficult for modern microprocessors.

Claims (1)

CLAIM A method of forming a color video image for projection systems including an optical system for combining images of primary colors, characterized in that three images of primary colors are side-by-side formed on the screen of one single-beam high-brightness tube, pre-exposing the video signal to software processing in order to divide it into three components of primary colors, for obtaining the necessary raster, in which each image of primary colors is located on the phosphor of its own color.