[ptx] Best way to compensate for different exposure/metering/white balance settings

[Florian Merz]

Hi list,

> I'm trying to create a panorama out of five photos that I took recently,
> but unfortunately I took the photos before reading about fixing the
> metering/white balance when taking shots for a panorama. I've created a
> test panorama that I'm quite happy with, but there are obvious problems
> with the photos having different exposure settings (showing up as
> gradients along the stitch lines).

I'm currently working on a solution for this problem based on the 
paper 'Radiometric Self Calibration' by Mitsunaga and Nayar [1].

My current approach is to write the panorama to a multi-layered tiff file 
using hugin so I don't have to care about panorama generation.

The first part of the tool then uses this tiff file and a handcrafted script 
file to extract those pixel pairs from the overlapping areas that will lead 
to the best results (reducing errors due to noise, saturation etc.).

The second part of the tool uses these pixel pairs to regenerate the 
response function as well as the exposure ratios.

This information can then be used to restore a uniform brightness (and hue) 
for all images used in the panorama. Alternatively a HRD image might be 
generated with this information. I haven't decided on my approach, yet.

The algorithm is specifically for exposure (and limited white balance) 
correction. If the change in color or brightness between the images is due 
to a change in the scene - for example panoramas taken at sunrise or 
sunset - this algorithm will fail. I don't even know how well it will work 
out at all, but that's why I'm doing it :)

> In case it helps, I've put up the panorama here:
> http://www.carbon.eclipse.co.uk/panorama.jpg
> and the original photos (including their exif data) here:
> http://www.carbon.eclipse.co.uk/DSCN0396.JPG
> http://www.carbon.eclipse.co.uk/DSCN0397.JPG
> http://www.carbon.eclipse.co.uk/DSCN0398.JPG
> http://www.carbon.eclipse.co.uk/DSCN0399.JPG
> http://www.carbon.eclipse.co.uk/DSCN0400.JPG

If this is ok with you I'd like to use your pictures for experimentation.

> Many thanks in advance for any advice you can offer,
> Jaime

Hope you all like it and feel free to comment or ask questions.

Greetings,
 Florian

p.s: I'd like to add this to the panorama tools once it's done.

[1] http://www.cs.columbia.edu/CAVE/publinks/mitsunaga_CVPR_1999.pdf