Scor­pio News


April–June 1988 – Volume 2. Issue 2.

Page 34 of 35

There’s also two ways of making the computer do the compression, either by software or by hardware. The end result is the same, but the benefits of one method against the other can be pretty dramatic. Software is very much more flexible than dedicated hardware, say, by being able to switch algorithm for best the results under a given circumstance, and software is always cheaper in quantity. But given the average PC type computer, dedicated hardware wins every time on the speed front. Even the latest super fast PC type computers using the 80386 and 68030 microprocessors can’t beat, or even come close to speed of using dedicated hardware. Dedicated hardware is more expensive and once designed, is inflexible by comparison as each added algorithm adds substantially to the cost, but even this inflexibility can be an advantage. It means that all images compressed in hardware will at least have the same type of compression, so that when transmitting images to other systems, means the receiving system only has the one type of compression to contend with. In the main, software compression is left to the big imaging systems which use mini-computers which have the edge in speed, but at a cost.

Now the degree of compression leads to advertising gimmick number 2. How many images on a disk. Now I’ve seen all sorts of claims, here are a few:
Upto 40,000
Over 60,000
Between 30,000 and 60,000
.. and so on.
This is really like asking ‘How long is a piece of string ?’. The number of images on a disk will depend on how much capacity the disk has and how well the images compress. The first is easily answered, ask how big the disk is ! The second – well – that’s a dodgy one. It depends on the document itself and it depends on the particular compression algorithm used. I’ve compressed a good many images testing our system, and I wouldn’t like to be drawn on exactly how well anything will compress. It’s even theoretically possible for an image to compress bigger than it started, although I’ve tried make it happen – I’ve never actually seen it happen. Let’s play safe. The worst I’ve seen is about 3:1, that’s a compression to one third the original size, that would give a rock bottom minimum of 6,000 images on a 2 Gbyte 12″ disk (definition – Gbyte is a Giga-byte that’s 1 x 109 or 1,000,000,000 bytes). On the other hand, the best I’ve seen is over 100:1 which would give over 200,000 images on the same disk. Who knows. All I’m prepared to say is at an informed guess, the Upto 40,000’ is probably near right, given average typescript documentation, and the ‘Upto’ is an old advertisers ploy, as ‘Upto’ includes any number less than the number quoted. Ever fallen for that one ? Seen a sale sign which says “Upto 50% discount on widgets”; what that means is that they’ve got one widget with 50% off and rest aren’t discounted at all ! Quite legal.

Anyway, that’s all for this issue.
Copyright: D. R. Hunt. © 1988.

Page 34 of 35