[ptx] Vignetting correction in nona

[Bruno Postle]

On Mon 02-Jan-2006 at 10:33 +0100, pablo.dangelo at informatik.uni-ulm.de wrote:
>
> I'm currently implementing a vignetting correction during remapping.

> The correction offset/factor can be specified by a polynomial 
> which depends on the normalized distance r (0..1) between point 
> (x,y) and the image center.

Have you considered a cosine rule?  I know it isn't as flexible or 
fast as a polynomial and only accounts for one type of vignetting, 
but since the angle of view of the photo is known it wouldn't 
require any calibration or manual tweaking.

Enblend does such a good job with vignetting already, perhaps this 
is all that is needed to get a good result in most use cases.

> Any further wishes or thoughts?

Thomas Niemann's 16bit panotools photoshop plugin had a problem with 
banding caused by vignetting correction.  The solution was to dither 
it, though I can't remember if this was added to the plugin or 
pano12.  The plugin is in sourceforge CVS:

  http://cvs.sourceforge.net/viewcvs.py/panotools/ptfilter/

-- 
Bruno