Gray scale system for visual displays

Abstract

An image is projected in gray scale on a large screen without any flicker, the different colors or shades being indicated on the screen by individual shades of gray. The image is defined by a plurality of pixels which are raster scanned. At each pixel position, a plurality of first digital signals are generated each representing an individual primary color (e.g. red, green and blue) or shade in the image at the position. Second digital signals individually representing such different colors or shades are also produced on a pseudo-random basis -e.g. by producing video clocked signals not only at the pixel positions but also during the horizontal and vertical retraces. The second signals are repetitively counted to a particular value to correspond to successive frames in the video image. In each successive frame, the first signals are compared in value with the second signals at each individual pixel position. A video signal is produced for generating the image for that pixel on the large screen only when the first signals for each pixel in a raster scan have a greater digital significance than, or an equal significance to, the second signals for that pixel in that raster scan. In each repetive count of frames to the particular value, a video signal is produced for each pixel in a number of frames dependent upon the digital significance of the first digital signals for that pixel. However, such video signals are produced for each pixel in a different pattern in each repetitive count to the particular value so as to eliminate any flicker in the video image on the large screen for that pixel.