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2007.01.31 17:01 "Re: 16bit grayscale with colormap", by Bob Friesenhahn
On Wed, 31 Jan 2007, Reinhard Mayr aka Czerwinski wrote: > I deal with 16bit grayscale TIFFs. The files originate from a 12bit CCD, > so the linear conversion 16bit->8bit turns my image almost black. > > To cope with that, I would like to add a ColorMap into the TIFF. For > testing, I altered an existing 16bit file: > o photometrics = 3 (ColorMap) > o added a colormap (tag 0140), length: 3*2^16= 196608 bytes > > Porgrams either refuse this file (ImageMagick viewer) or ignore the > colormap and treat as if without (ImageJ). > > Is this a proper interpretation of the TIFF specs (TIFF6 specs p.23 > allow only 4/8 bits per sample -- why?)? How can I work with the > data in terms of leaving original values untouched and just change a > LUT/ColorMap/whatever? Give development GraphicsMagick 1.2 (built with 16-bit quantums) a try. I have written and read TIFFs with 64K colormap entries (16 bit indexes) using development GraphicsMagick 1.2. As I recall, the writing was extremely slow since the colormap was deduced from a truecolor image but the reading is pretty quick. Are you able to provide a sample file? Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/