8.4 Image Display Systems

Image display is used for displaying digital image data into a visual color image as a tool for real time "man-machine interface". An image display system consists of a frame buffer, look up table, D/A converter and a display, as shown in Figure 8.4.1.

Frame buffer is an image memory to allow high speed reading of digital image data. The size of the image memory is usually 512 x 512 to 2048 x 2048 picture elements.

Look up table is a pre-set function to enable conversion from an input signal to an output signal in real time. Linear function, contrast enhancement function, gamma function, log function etc. are mostly used, as shown in Figure 8.4.2. D/A converter converts digital image data in a frame buffer to an analog video signal.

Figure 8.4.3 shows R, G, B separate type as the D/A output system, while Figure 8.4.4 shows the color map type. The former system has an independent frame buffer and look up table with respect to R, G, B, which enables individual color control. Thus full color images (256 x 256 x 256 = 16,787,216 colors) can be generated. The latter system has a unified frame buffer and a R, G, B separate look up table, which only allows generation of a limited number of colors, for example 256 colors in the case of a combination of 8 bits of frame buffer and 8 bits to each of R, G, B.

There are several types of display; CRT, liquid crystal display, plasma display, for example.


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