On (17 Mar 97) Herman Schonfeld wrote to Jerry Coffin...
 JC>That would cover at least PCX and BMP files.  Either _can_ be
 JC>compressed, but neither requires it.  However, it might be
 JC>worthwhile to support compression as well: both use RLE which is
 JC>quite easy to decompress.
 HS> RLE's aren't just the answer for compression. Your better of storing
 HS> your bitmaps in a datafile which is compressed using LZSS algorithm.
 HS> When you load your bitmaps your only loading a much smaller version
 HS> (saves alot of disk reading, which can get very annoying in a game
 HS> etc) and use an advanced RLE method, or using DCT coding (with lookup
 HS> tables) can prove VERY efficient.
 HS> DCT coding is the same method used to compress jpeg's.
The original question was about formats that didn't require any
compression at all.  I was merely pointing out that while RLE IS
compression, it's extremely simple so there's rarely a reason to exclude
supporting it.
This is less true of LZ based compression: while not _terribly_ complex,
these certainly require a LOT more work than uncompressed or RLE images.
It's FAR from true of DCT, which is quite complex, and generally MUCH
slower than the preceding alternatives.  Finally, DCT is a lossy
compression, and the amount of compression it achieves depends largely
upon the amount of deterioration of the image you allow.  The idea is to
find a balance where you get minimal loss of quality in exchange for a
substantial improvement in compression.  However, in some cases even a
minimal loss of quality isn't acceptable.
Finally, I'd note that which will work best depends heavily on the type
of images you're working with.  DCT works well for more or less
photographic type images, but does far less with, say, line drawings.
For many line drawings and similar items, RLE will produce nearly the
same comrpession as other forms, but with far less work.
    Later,
    Jerry.
... The Universe is a figment of its own imagination.
--- PPoint 1.90
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