2007.01.31 16:56 "Re: [Tiff] 16bit grayscale with colormap", by Toby Thain

On 31-Jan-07, at 2:39 PM, 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.

Maybe I'm missing something, but why don't you just multiply by 16 before storing in TIFF?

--Toby

To cope with that, I would like to add a ColorMap into the TIFF. For testing, I altered an existing 16bit file:

• photometrics = 3 (ColorMap)
• 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?

Thanks for all advices, hints & pointers!

Cz.

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