xanthian@zorch.SF-Bay.ORG (Kent Paul Dolan) (09/07/90)
Just a quick single data point for the discussion. I just compressed the ASCII picture description data "StPauls.dat" that came as part of the DBKtrace raytracing package recently posted in comp.{sources,binaries}.amiga. It is highly repetitive data of the kind typical of images (lots of "0000"s). The original file size was 863,908 bytes. Compressed with zoo (which uses Lempel-Ziv compression, I understand, probably 12 bits, considering the target machines on which it has to unpack), the file compressed to 131,184 bytes (no header, inode, etc. overhead counted before or after); using the Amiga version of "compress" (almost certainly 14 bits), the output file was 121,048 bytes, while using the recently distributed lharc (in comp.sources.misc, though I'm using the Amiga version) archiver, which combines adaptive (I think) Huffman encoding with LZ compression, the same file compressed to 49,974 bytes! That is big bucks savings for the net, and the improvement in compressing general text data (i.e., news) with lharc is almost as incredible. If that kind of savings hold for a wider range of test data, and for real raw image pixel data (I have none for a test), that is so spectacular an improvement that I urge someone to write a utility to take a GIF file, yank out (decompress) the raw image data, compress it with the algorithm from lharc and stuff it back in the rest of the GIF wrapper to make a GIFLZH file (and vice versa) and that that become the net image data publication and storage format while we look for something even better. The reason for doing it as a GIF <-> GIFLZH rather than raw <-> GIFLZH utility is to avoid (for now) invalidating all the GIF viewers in the universe. End users with lots of disk space can choose to convert to GIF for storage and speed of display, while the net and BBSs get the distribution and storage savings of GIFLZH. To see if this is worthwhile, I urge anyone with lharc, compress, and a bunch of raw image data files to do a more comprehensive test and report back to the net. Thanks! Kent, the man from xanth. <xanthian@Zorch.SF-Bay.ORG> <xanthian@well.sf.ca.us>