Bulletin Spring‧Summer 1994

A Picture Costs More than a Thousand Words The role of two-dimensional integer cosine transforms in image compression Image Storage Problems There are very few people at CUHK who do not use a word processor. But a 'picture is worth a thousand words', and indeed pictures are much more costly to process, transmit and store. For example, this article has about 1,000 words, and can be represented by about 40,000 bits. A floppy disk stores about 10 million bits, or 10 Mb, good for 250 articles of this length. One TV picture, on the other hand, is made up of some 250,000 little pixels, which will require 6 Mb to store, about 60 per cent of a floppy disk. As pictures are renewed 25 times a second on the TV screen, we are talking about 150 Mb per second. I f that is hard to grasp, it means 54,000 floppy disks for storing one hour's worth of programme, not a very practical solution. Image Transmission Problems The transmission of pictures faces a similar problem. It is true that optical fibres can now carry thousands of Mb per second, but this would accommodate only a handful of TV channels if pictures are transmitted 'raw' or untreated. People are now talking about 'video on demand', in which a million households Research Projects 8