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December 1994
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1994.12.16 22:04 "Re: JBIG compression", by Rick Richardson
Kyriakos Georgiou writes... > > In response to Sam's comments: > > > Also, can the current libtiff G4 decompression implementation be > > improved ? What sort of improvements can be expected ? > > > > What's wrong with the current implementation? > > The current implementation is fine, but.. I have in my hands a commercial > product (no source) that does decompression in noticable less time. > That suggests that there are faster ways to decompress G4 in software, > alas my question. I cannot speak for the G4 decompression in libtiff, but I can vouch for the fact that the libtiff G3 decompression is not as fast as at least my own implementation. However, I am not at liberty to provide the source code since it belongs to my employer. In my experience with G3, I found the fastest way was to completely unroll the decompression. I tried numerous different 'elegant' algorithmic approaches over a period of about 3 years and discovered that the simple brute force unrolled approach was always fastest. The decoder itself is something like 700 lines of nested C language if-else statements. I did not write those 700 lines, though. Instead, I wrote a program that wrote those lines for me. From time to time, I've been tempted to change the decoder-generator program to output assembler instead of C code. I think that would ultimately be the fastest possible implementation for any particular architecture (with the exception of a full lookup table which takes up an impractical amount of RAM on typical machines available today). -- Rick Richardson Senior Staff Engineer Visit my WWW home page: DigiBoard APD Email: rick@digibd.com http://www.digibd.com/people/rick 6801 Shady Oak Rd. Fax: (612) 947-1129 Eden Prarie, MN 55344 Tel: (612) 947-1111 <standard disclaimer>