LibTiff Mailing List
TIFF and LibTiff Mailing List Archive
December 1994
Previous Thread
Next Thread
Previous by Thread
Next by Thread
Previous by Date
Next by Date
Contact
The TIFF Mailing List Homepage
This list is run by Frank Warmerdam
Archive maintained by AWare Systems
Thread
1994.12.15 09:59 "Further G4 improvement", by Karsten Spang
In message <m0rI1kN-0007zYC@mykonos.rc.rit.edu> ,
kg@mykonos.rc.rit.edu (Kyriakos Georgiou) writes:
>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:-)
Karsten
--------------------------------------------------------------------------------
E-mail: krs@kampsax.dk Karsten Spang
Phone: +45 36 39 07 88 Kampsax Data
Fax: +45 36 77 03 01 P.O. Box 1142
DK-2650 Hvidovre
Denmark