On 08/09/2010 04:16 PM, Charlie De wrote:
>> From Rupert:
>>       (as far as I can tell, the current Decompose Lab  functions are
>>       broken, anyway).
>
> What makes you say that?  And how severe is the problem?
>
> Right this minute I'm writing a script with LAB Decompose...

Well, 'different' might have been nicer than 'broken' -

The conversion doesn't account for gamma:
        http://www.brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html

As a result, the L* channel is very light (check the histogram). I have 
no clue how that influences a* and b*.

Also, it uses the conversion matrix for PAL/SECAM RGB. (Maybe PAL/SECAM 
has gamma 1.0? Then the missing gamma correction would be correct.)
        http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html

Anyway, unless your image is in PAL/SECAM RGB, the conversion in 
Decompose is incorrect.
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