Ron noted: >Got a nice big (just over 1 MB) .BMP and zipped it >to .ZBM. > > The zip was reduced to about 85 % of the original .BMP. :( > > That is obviously not good enough, so what did I miss ? G'day Ron. Your big bitmap was a photo, I wager. Clarence has been zipping bitmaps of screenshots of mainly text webpages, which have larger regions of single color. If these have their color-depth increased so that they may be saved as JPEGs the resultant files are larger than ZBM, GIF or PNG and the text will look antialiased (fuzzy). Here's a list of results from compressing a small photo: Image Compression Tests *********************** Original: 263,254 bitmap Zipped 220,543 = 83.8% of original 10% JPEG: 38,272 = 14.5% 20% JPEG: 25,301 = 9.6% 30% JPEG: 20,011 = 7.6% minor degradation visible 40% JPEG: 16,709 = 6.3% 50% JPEG: 14,673 = 5.6% 60% JPEG: 12,816 = 4.9% degradation actually improves faint verticals 70% JPEG: 10,949 = 4.2% 80% JPEG: 8,630 = 3.3% quite noticeable degradation 90% JPEG: 5,931 = 2.3% poor 99% JPEG: 3,431 = 1.3% unusable 24bit PNG: 191,180 = 72.6% 8bit PNG: 55,988 = 21.3% 8bit GIF: 40,261 = 15.3% (24bit = 16 million colors; 8bit = 256 colors, the maximum for GIF) The percentages spec'ed for the JPEGs are only some sort of guide in Paint Shop Pro; I generally use 20 - 40%. PNG seems to be better at simpler, diagrammatic images, but isn't as efficient as ZBM. Buttons and small images saved as GIFS rather than JPEGs will generally produce smaller filesizes (and display faster in Arachne), particularly if the color-depth can be reduced. PhotoShop adds header information that can considerably inflate the filesize. Regards, Jake Young
