AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

1993.12.16 19:52 "Group3 compressed tiffs with bit errors sans EOLS", by Ronald Danisewicz

I work for Xerox Imaging Systems and we are regular xv users. One thing that impressed us about xv 2.21 is that it seems to be able to handle Group III compressed tiff files that seem to have bit errors in them, yet lack EOLs.

John Bradley told me that xv uses the famous Leffler library, which we have, but I guess we have an outdated version, because it chokes on such files.

Could anyone tell us the method that the "new" Leffler code uses to synch up to the beginning of an encoded line after encountering an error in such files without EOLs?

We guess that the routine keeps trying to start the line on next byte until it finds a starting byte that starts a sequence whose decoded runs add up to the correct line width? But this seems pretty outlandish.

But if this is the case, how the heck do such files come into existence? Is there some really silly PC fax software out there that just strips out EOLS from the raw compressed data stream after demodulation and just zonks this raw data into a tiff file, bit errors and all. I always imagined that any reasonable fax software would decompress the data, check for errors, and do whatever it could to make sure the tiff file it outputs is valid. If they don't do this, then why do they remove the EOLS? This just makes it harder to synch up after errors.