[argyllcms] Re: Obtaining a camera color response matrix

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 13 Mar 2015 16:27:41 +0100

Am 13.03.2015 um 15:07 schrieb Nikolai Tasev:

I do not know the calculations of the gamma encoding

It's eventually a power function, X_linear = X_encoded ^ gamma, which is 
applied to each of the three channels individually (assuming that the channels 
normalized to a 0..1 range).

Does the sRGB color space imply that the RGB values are already encoded with some gamma? That is to be truly in sRGB color space you have to apply gamma encode on the linear values?

sRGB has by definition a non-linear encoding. It's not excatly a power function 
though, but the overall tone reproduction curve is at least similar to a power 
function with gamma=2.2.
See also http://en.wikipedia.org/wiki/SRGB

So what effect of the gamma encoding should I include in the matrix 

A matrix transformation is intended for linear RGB (the same applies to 
offsets), so you need to convert non-linearly encoded source RGB data to linear 
RGB first, then apply the matrix, and finally apply the non-linear encoding of 
the output RGB color space.


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