the keystone correction formula uses a perspective correction approach
(i.e. image plane x and y shortening is proportional to 1/z in 3d and
different for every pixel, much like
http://en.wikipedia.org/wiki/Texture_mapping#Perspective_correctness). i
don't see why you would need additional constant scaling?
-jo
On Thu, May 30, 2013 at 8:46 AM, Leonard Evens
<[email protected]>wrote:
> Sometimes, after correcting either vertical or horizontal keystoning,
> so that the lines I want parallel are parallel, I also want to change the
> vertical or horizontal scaling. That is necessary because the keystoning
> correction alone may not yield the right scale. If one knows the
> position of
> the lens and the actual dimensions of the building, or if one knows the
> position of the lens and the angle at which the lens axis points, one can
> calculate the proper scaling, but, while the lens position may be in the
> exif info, the other information is not. So one has to correct the scale
> by eyeballing it.
>
> I can't find a darktable plugin to do it.
>
> Leonard Evens [email protected]
> Professor Emeritus, Department of Mathematics, Northwestern University
>
>
>
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