radford@calgary.UUCP (08/11/86)
In article <5963@sun.uucp>, chuq@sun.uucp (Chuq Von Rospach; Lord of the OtherRealms) writes: > > I was reading an post on the local bulletin board that rumored Apple had > > come up with an algorithm for shrinking paint documents in a 31:1 ratio. > > Imagine a 31K picture saved as 1K on disk. Wow. > > Wow is right. The rumor is almost definitely wrong. Compression technology > of a random bitstream is lucky to get 50% compaction. The compress program > used for passing news around averages between 35% and 45%. It is theoretically impossible to compress a *random* bit stream at all. Maybe you meant "typical". > This may be a "best case" compression, something unrealistic like a Macpaint > image of all white or black pixels (neither of them very useful). I doubt > seriously they can get even close to that on a normal bitmap. Think about > it logically -- a 31:1 ratio implies that each bit in the compressed file > needs to hold information to recreate 31 other bits. Not very realistic. A 31:1 compression ratio would certainly be impressive. It's no doubt impossible for something like a digitized image or a real "painting", but for your typical diagram with a couple of boxes and a few lines of text it isn't beyond the bounds of possibility. There's a lot of empty space in such a picture. To check this, consider how little space the *input* (mouse positions and keystrokes) required to make such a picture would need to take. Radford Neal The University of Calgary