LibTiff Mailing List
TIFF and LibTiff Mailing List Archive
December 2001
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
2001.12.25 03:35 "Re: Where is the best place to find compression algorithm", by Jon Saxton
> > Where is the best place to find the algorithms for CCITT Group3 and 4. > > I am putting this on another machine. > > I'll second that- I'm close enough with my old tiff program that > incorporating the whole tifflib would probably be more effort than just > rolling my own for these two cases. Dave, Harry: About three years ago I needed to strip extraneous white space from some G4 images and at the time I searched around the internet for a while to locate information. Descriptions of the algorithms are fairly easy to get but source code is a different story. I had my own TIFF handling code in C++, completely independent of libtiff but I found that the easiest route was to very carefully tease out the G3/G4 codecs from the libtiff sources and incorporate those into my code. The exposed interface contained just three routines, Fax4Encode(), Fax4Decode() and Fax3PreDecode() along with a somewhat stripped-down codec state block. I didn't do the extra step and build a class to encapsulate everything but at least now I can decode, manipulate and encode all in memory. The whole exercise took maybe 3-4 days but in the end it was well worth the effort. The beauty of the libtiff code is that it has been around for a long time now. In particular, the G3/G4 codecs are very stable and probably thoroughly debugged. Rolling your own might turn out to be more difficult. -- Jon Saxton <js@triton.vg> OS/2 software developer U.S. agent for Triton Technologies International Ltd http://www.triton.vg/