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TIFF and LibTiff Mail List Archive

Thread

1998.07.08 15:09 "CIE L*a*b* color", by Joe Longo
1998.07.09 12:53 "RE: CIE L*a*b* color", by Martí Maria

1998.07.09 12:53 "RE: CIE L*a*b* color", by Martí Maria

Hello,

The library has a TIFFTAG_PHOTOMETRIC value for CIE L*a*b* color,

#define     PHOTOMETRIC_CIELAB          8       /* !1976 CIE L*a*b* */

but no code for color conversion (to RGB in particular) Has anyone used this?

I'm wishing for a simple conversion of the 3 bytes of L*a*b* to RGB?

I'm sorry to say that there is no "simple" way to covert from/to Lab <-> RGB. CIE L*a*b is a device independent way to describe colors, due that, the conversion process involves knowing some info about the target device RGB. White point, gamma response, primary chromacities... etc.

You can find a very useful discussion about this stuff on:

        http://home.inforamp.net/~poynton/GammaFAQ.html

and

        http://home.inforamp.net/~poynton/ColorFAQ.html

I'm currently doing this using output ICC profiles. Check if your target platform has Color Management System, (Windows and Mac both have CMS at system level). The CMS can handle transparently this conversion for you.

Regards.
Martí Maria
ICR