TIFF and LibTiff Mail List Archive


1994.12.14 22:00 "JBIG compression", by Kyriakos Georgiou
1994.12.14 23:51 "Re: JBIG compression", by Sam Leffler
1994.12.16 18:00 "Re: JBIG compression", by Fredrik Lundh
1994.12.16 21:02 "Re: JBIG compression", by Kyriakos Georgiou
1994.12.16 21:17 "Re: JBIG compression", by Sam Leffler
1994.12.16 22:04 "Re: JBIG compression", by Rick Richardson
1994.12.16 22:18 "Re: JBIG compression (really G3/G4 decompression)", by Sam Leffler
1994.12.15 09:59 "Further G4 improvement", by Karsten Spang

1994.12.15 09:59 "Further G4 improvement", by Karsten Spang

I was surprised to find a reference to J.D.Murray, W.vanRyper, "Encyclopedia of Graphics File Formats", O'Reilly & Associates, Inc. 1994, pp.148 which stated that some implementations of G4 encode as fast as G3, and decode even faster.

I have an idea. What if the reference line was represented as a list of change positions? That would eliminate the need for half of the findspan()'s in the encoding, and all of them in the decoding. In other words, what remains is the same as for G3, with just a little overhead searching the list. In most cases, this search would be just a few steps forward.

I don't see how this can be *faster* than G3, except that you have to produce/decode Huffmann codes which are generally shorter for G4 than for G3. After all this is what makes G4 compression better than G3 compression.

I intend to implement this at some future time, but I cannot make any promises as to when I will do it.

If anybody else wants to give it a try, please inform me as I don't want to repeat your work:-)

E-mail:                                      Karsten Spang
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