First we consider the spatial size of analogue video when compared to the common formats for digital video standards. A PAL television displays video as 625 lines and an NTSC television displays 525 lines. Most common formats for digital video are related to the visible area for each of the television standards. It can be seen that digital images are all smaller than current television sizes. Moreover, television images are significantly smaller than current workstation screen sizes which are commonly of the order 1200 x 1000 pixels.
Digital video utilizes even less of a workstation screen.
If we assume that there are 24 bits per pixel in the digital video and 30 frames per second, the amount of disc space required for such a stream of full-motion video is shown in table 4.2 . We can see that 1 hour of video with a resolution of 640 x 480 would consume 97 Gb of disc space, which is significantly larger than most storage devices. However, although there are devices that can store this amount of data, there are currently no digital storage devices which could store 97 Gb on half a device which is the size of a video cassette. Rowe has also estimated the amount of space used when compression techniques are used. Table 4.3 shows the space needed when compressing video of size 640 x 480 pixels, and table 4.4 shows the space used when compressing video of size 320 x 240 pixels.