5-4 Image Display

An image display is to display a vector map or image data on a color monitor. An image display consists of frame buffer, look up table, D/A converter and monitor (or called display) as shown in Figure 5.2.

Frame Buffer
Frame buffer is a memory device that stores the image data and reads at memory board. The memory capacity ranges 512 x 512 x 3 bytes to 2,048 x 2,048 x 3 bytes.

Look Up Table
User can assign a look up table that makes image transformation in real time. The table includes linear function, gamma function, log function etc. as shown in Figure 5.3.

D/A Converter
D/A converter will convert digital image data to analog video signals of red (R), green(G) and blue(B) for image display on an analog color monitor.
The video signals will be usually NTSC in interlace mode or RGB independent in non-interlace mode, with 525 scan lines or pixels typically. High vision video with high resolution of 1,024 scan lines is now becoming available.

Monitor (Display)
Converted analog video signals are displayed on a monitor of CRT (cathode ray tube) or liquid crystal monitor.

Image display is classified into two types:

RGB type
Independent frame buffer and look up table is installed to each primary color of R, G and B. Full color means that 8 bits are assigned to R, G and B which makes 256 x 256 x 256 = 16,777,216 colors. (see Figure 5.4)

Color Map type
A limited and integrated frame buffer and look up table are installed in rather cheaper display. For example, in case of only 8 bits for frame buffer and look up table, only 256 colors will be generated (see Figure 5.5).