PanoTools:
Re: My attempt to eliminate vignetting effect
Erik Krause 2004-Dec-02 17:50:44
JD Smith <#removed#> wrote:
> > What do you think: In a 30% overlap is there enough information to do a
> > fairly exact determination of vignetting? I think it should be possible
> > but that's only a feeling...
>
> Well, it depends on what you mean by exact. If you come much closer
> to the structure of the mismatch by assuming a radially symmetric
> function centered at [w/2,h/2], you should be able to make real
> improvements to the results enblend delivers, which are already very
> good. Remember that enblend knows nothing about the large scale
> spatial structure of the mismatch.
In a low spatial frequency version of the image there should be a
gradient in brightness. For low spatial frequency the contens of the
overlap region should be the same for two adjacent images - small
misalignments shouldn't make any difference.
If there is a gradient caused by vignetting it could be determined from
the overlap region(s) and estimated for the rest of the image by simply
looking at the difference in the overlap region.
I think this way a program does not need to have any information about
the spatial structure of the mismatch. It simply adjusts difference to
zero.
If I understood correctly this is what enblend achieves by averaging
the overlap region for different spatial frequencies. What it currently
does not is to assume that all images where taken with the same lens at
the same settings and correct these images even if the overlap region
is smaller (f.e. due to handheld shooting).
A program could even output a flat field image calculated from two or
three images with 50% overlap...
--
Erik Krause
Digital contrast problems: http://www.erik-krause.de/contrast
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