2005.03.22 18:22 "Re: [Tiff] tif_jpeg.c and 12bit JPEG Files", by Bob Friesenhahn
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.
Yes, it is my hope to do a test build this way and verify that things work properly. As far as I can tell the current tif_jpeg.c does not repack the 16bit values returned by libjpeg6b (in 12bitmode) to 12bit. Folks have apparently used this form, but I don't really know how they make it work.
Maybe these `folks' would care to identify themselves if they do actually exist? It may be that they made it work by hacking their private copy of the code.
The only way that makes sense is for 12 bit samples to be returned the same as for an uncompressed 12 bit TIFF file. Likewise, 12 bit samples should be consumed so that the only thing special the library user needs to do is request JPEG compression, and possibly JPEG RGB mode.
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/