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2006.09.26 13:38 "Re: Status of ISO JBIG and CIELAB JPEG support", by Joris Van Damme
Wandering, A Wandering LibTIFF User wrote: > I should ask Lee what his intentions were with these patches to > libjpeg/libtiff. It sounds like building colour conversion code into > his end-client (Hylafax) was the correct place to make changes, and > to make only minimal changes to the lib[jpeg|tiff] to ensure they > didn't reject the datastreams. You and I think so. I've raised the same points to John Barber I think was his name at the time the first patch came to see the day of light. I've never saw convincing arguments to do otherwise. Still, everybody seems to prefer throwing patches at stuff. > > I've some, or at the very least I had some... I'll try and find > > them and get back to you later today. > > I would love to get them, still. Thanks! Yeah, I forgot looking for them. I'm about to leave the office now, though, but I'll write myself a note to remind me when I return. > What a mess. In my naivete, I'd thought that JPEG handled "true > colour" data as tri-planar data, but I suppose the temptations to use > subsampling for the colour component was too irresistable. It wasn't just temptation... Lee Howard set out to embed an existing JPEG stream inside JPEG. The existing JPEG stream was as he got it from a fax line. The goal was to take advantage of the fact TIFF is able to store multiple pages, whilst JPEG is not, and still change as little as possible in the actual receiving end, certainly do no actual decompression/recompression or anything. > > I'm unable to answer these questions, best I can do is provide > > theoretical background and file analysis. I will also try and find > > the ITULAB JPEG images that at least at one time were part of my > > testimage library. > > I would appreciate links to what are hopefully "reference" images > that reflect the correct output according to spec. I've a few ITULAB JPEGs that are somewhat of a reference, like I said, and I'll try and find them. As to ITULAB, the sortoff spec is an RFC, I think RFC number was 2301. As to CIE and ICC Lab, the reference that is pointed to most is a thread in this mailing list, by the hand of Marti Maria, http://www.asmail.be/msg0055212264.html. IIRC, there's more or less the same story in the second TIFF specification suplement (but do check, memory can deceive). I've some CIE and ICC and ITU Lab TIFF images, but at this time I'm in between versions of my codec, and unable to check which is which and which is valid, so I hesitate to share them right now as I've no means to be sure I wouldn't be misleading you. Best regards, Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html