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March 2005
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2005.03.22 18:04 "Re: tif_jpeg.c and 12bit JPEG Files", by Bob Friesenhahn
On Tue, 22 Mar 2005, Frank Warmerdam wrote: > > My general intent then is to modify the tif_jpeg.c JPEGDecode() > (and likely JPEGEncode()) to support repacking 12bit data from > 16 bit JSAMPLEs returned by libjpeg into packed 12bit format in > the TIFF buffer. This seems to be the main barrier to correct operation > currently. But there are a few other patches needed, and also the > ability to autodetect at build time which style of libjpeg is being used. > The traditional "6b" libjpeg, or the newer "Mk1". This sounds good to me. As I mentioned in a prior email, libtiff needs to provide an interface (probably styled like a tag) which supports testing for the supported JPEG bit depths. Without this, applications which could support 8 bits, 12 bits, or both in the same build, will not know what libtiff supports and may request a depth which causes gruesome errors later on. > BTW, the 6b libjpeg has to be built either in 8bit mode or 12bit mode. > One build of the library cannot support both forms. The new Mk1 > library always returns samples as 16 samples and can read either > 8bit or 12bit files dynamically. Libtiff should also support 12 bits using 6b libjpeg if possible. I believe that the interface is compatible since it looks like the "Mk1" interface. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/