Joseph Heled writes:
>  How (or can you) combine errors/noise in HSV into one error/noise 
> figure which reflects the total "human visual" error perception. 

HSV is the wrong colorspace to use for this purpose.  The LA*B*
colorspace was designed to do what you are trying to accomplish:
supposedly, equal distances in LA*B* coordinate space correspond to
equal distances in human perceptual space -- although I understand
that there is debate about whether this is really true.

(Of course, you have to be careful about what you are trying to do.
If you shift an entire image one pixel to the right, it will
probably look identical to a human although it may be quite different
on a pixel-for-pixel basis.  In general, integrating pixel-by-pixel
color differences will not give you a very accurate picture of
how much difference people perceive between two images.)

The "decompose" plug-in in Gimp will decompose an image into LAB
coordinates -- however, I looked at the source code recently in
connection with a bug report (bug #147603), and it seems that the
LA*B* algorithm is not correctly implemented by the plug-in, so you
should be cautious in using it for anything important.

  -- Bill

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