[ptx] Re: Brightness/colour correction in pano12 and nona

[Bruno Postle]

On Sun 20-Nov-2005 at 13:08 -0800, Rik Littlefield wrote:

> For example, you can expect less than perfect correction if radial
> falloff causes a left-to-right gradient in one image but
> right-to-left in the other.  Radial falloff should be corrected
> in each image separately, before attempting to correct one image
> against another.  (And accurately correcting for radial falloff
> requires knowing the actual light-level-to-pixel-value gradation
> curve, not just some idealized gamma, but that's another story.)

Actually, if you assume that two overlapping images have the same
radial falloff you should be able to infer this radial falloff (and
possibly the mapping-to-linear curve as well) with just the
difference in brightness for each pixel pair and the relative
distances to their photo centres.

This idea appeared on the panotools list a year ago:

  http://thread.gmane.org/gmane.comp.graphics.panotools/26390

..but this should be unnecessary if you are working with linear RAW
data in the first place, it should be possible to simply apply a
cosine-rule correction to each pixel based on the (known) angle of
view of the photo - this would only work with rectilinear images.

-- 
Bruno