hp0p+@andrew.cmu.edu (Hokkun Pang) (03/11/91)
what's the typical compression ratio for Window's bmp files? I just compressed a bmp file from 130k to 38k.
gjh@ecs.soton.ac.uk (Gary Hill) (03/11/91)
In <Qbqadfy00WAwEC0Htl@andrew.cmu.edu> hp0p+@andrew.cmu.edu (Hokkun Pang) writes: >what's the typical compression ratio for Window's bmp files? I just compressed >a bmp file from 130k to 38k. It depends on the number of colours used and the type of picture. Only 4 bit and 8 bit bitmaps are compressed, this is done using run length encoding, so if you have scanned bitmaps, the compression is next to useless due to lots of close, but not identical pictures. If you have something produced from Paintbrush say, then you can get much better compression rates because there are usually long runs of identical colours. Using wingif to compress scanned bitmaps (such as Cougar.bmp if you've seen it) the bitmap actually got bigger, whilst I got good ratios similar to yours on Paintbrush bitmaps. 1 bit bitmaps are small anyway, and 24 bit is tricky because each pixel is described absolutely and so they are harder to manipulate Hope this helps, Gary Hill, gjh@uk.ac.soton.ecs
cms2839@isc.rit.edu (a.stranger) (03/13/91)
In article <Qbqadfy00WAwEC0Htl@andrew.cmu.edu> hp0p+@andrew.cmu.edu (Hokkun Pang) writes: >what's the typical compression ratio for Window's bmp files? I just compressed >a bmp file from 130k to 38k. depends entirely on the contents of the bmp . complex , and especially dithered designs will have a smaller compression ratio , whereas designs with large fields of solid colour will compress tightly . -- @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ "Imagination keeps the shadows away - Xymox @ @~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~@ @ a.stranger - CMS2839@ritvax.isc.rit.edu @