Colour/brightness correction (was:hugin update)

[Bruno Postle]

On Mon 10-Nov-2003 at 06:59:39 +0100, Kai-Uwe Behrmann wrote:
> Am 10.11.03, 18:06 +0100 schrieb Pablo d'Angelo:
> 
> > speaking of gimp. Is there a plugin that can calculate curves,
> > based on two similar regions, like its done by PTStitcher?
> 
> Can You explain me what curves? Luminosity, warping ...

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

As I remember, ptstitcher works in this order:

  1. remaps each photo to the final projection
  2. adjusts colour/brightness between each picture pair (optional)
  3. feathers edges
  4. merges images

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

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

-- 
Bruno