Colour/brightness correction (was:hugin update)

[Pablo d'Angelo]

Hi,

> I'll dig Helmut's explanation out of my proj-imim archive, remind me
> if I forget.

I've just read
http://www.path.unimelb.edu.au/~dersch/cbcorrect/cb.html

> The colour/brightness adjustment works by calculating the biggest
> rectangle of overlapping area between a pair of images.

That article says that all overlapping pixels are used, except those cropped
away with the Sx1,x2,y1,y2 crop option.

> A colour
> histogram is calculated for both rectangles and one of the images is
> contrast/brightness adjusted until it's histogram approximates the
> histogram from the other.
> 
> I'm fairly sure that it doesn't do any curves/gamma adjustment.

Helmut's description says:

 "The algorithm now included in PTStitcher calculates gradation-curves for
  each colour channel which match the corresponding histograms."

> I have no idea how the solver works, maybe it actually draws
> histograms and does an XOR comparison of the histogram images.

  "The curves used for correction are calculated using a transformation of
   the histograms, and are exact (at least under usually applicable
   assumptions), not mere optimizations"

It would be nice to know this transformation :)

ciao
  Pablo
--
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