[Gimp-user] Use of lens distortion filter?

2011-04-03 Thread Leonard Evens
I asked about this once before without too much luck.  Let me try again.

I need to correct distortion from my 18-200 mm lens for my Nikon D80.

I can experiment with the controls until I get what looks reasonable,
but it would be easier if I could find recommendations for settings of
the lens distortion filter at different focal lengths for the lens.

I used to use a Panorama Tools plugin for gimp for which I found such
recommendations, but I can't get that plugin to work with recent
versions of gimp.

Of course I can experiment by photographing a grid at different focal
lengths and different subject distances and using trial and error, and
create myh own tables.  But, I hope someone has already done that.

Finally, where can I find a description of the the algorithm that the
filter uses.  If I had that, it might simplify things.   Usually these
algorithms apply a polynomial (usually cubic)  correction based on the
radial distance from the center of the image.  The parameters set the
coefficients of the polynomial.
-- 
Leonard Evens l...@math.northwestern.edu
Professor Emeritus, Department of Mathematics, Northwestern University

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Re: [Gimp-user] Use of lens distortion filter?

2011-04-03 Thread Alexandre Prokoudine
On 4/4/11, Leonard Evens wrote:
 I asked about this once before without too much luck.  Let me try again.

 I need to correct distortion from my 18-200 mm lens for my Nikon D80.

If you shoot to Raw, my suggestion is to use UI to LensFun in UFRaw.
You just select lens, distance to object and you are done (unless you
want tweaking variables that are the same as in panotools).

Additionally you can use darktable which has UI to LensFun as well,
but can work on JPEG too. But then you have to use Linux :)

There are even more photographty tools on Linux that can make use of LensFun.

Alexandre Prokoudine
http://libregraphicsworld.org
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