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From: "Martí María" <martim@abaforum.es>
To: "Joe Longo" <joel@flashpnt.com>, <tiff@sgi.com>
Subject: RE: CIE  L*a*b* color
Date: Thu, 9 Jul 1998 14:53:46 +0200
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   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


