Opening Lab color Tiff files with ColorLab

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Posted By
Chris_Cox
Apr 1, 2004
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398
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1
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Closed
weijason – start by reading the ICC profile specification …

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Roberto_G_Gonzalez
Apr 1, 2004
Well, I think I have solved the problem. The answer is simple. ColorLab encodes differently the a & b values in the file. They don’t use CIE or ICC encoding. They use their own encoding. I’ve made a MatLab small routine to change the values and it works at least reading. I have not made the writing procedure so that my files will look good in ColorLab. Unfortunately, MatLab will make a conversion from CIE lab to ICC lab automatically depending on the platform you are using. I have noticed that in my windows 2000 computer the conversion is not done. On my Windows XP pro the conversion is done automatically. So, the routine to use seems platform dependant. It’s a pitty that such good book shows a procedure that doesn’t work.

On the question asked on how to convert RGB to Lab values, probably the icc profile -if you have one- should be a simple matrix one and that is precisely the matrix that you need to use. (Or maybe the inverse, depends on what direction the conversion you are looking for). If an icc profile of the RGB space is not available, then you need to find out what kind of RGB is. There are several RGB spaces and the conversion matrix is different for each an every one of them.
The following link has a lot of information on how to convert different color spaces: <http://www.brucelindbloom.com/>
Hope this helps.

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