Re: [Gimp-user] Unskewing images of flat rectangular objects in Gimp

[Elmer Wix <elmer cabekaziruronometu wix gmail com>]

Øyvind Kolås <pippin gimp org> wrote:
> On Mon, Feb 4, 2013 at 4:11 PM, Elmer Wix
> <elmer cabekaziruronometu wix gmail com> wrote:
> > I often use my digital camera to take pictures of flat, rectangular
> > objects, like framed paintings on a wall, book or album covers, or
> > pages of documents.  Of course, I can't take these pictures straight
> > on and perfectly level, but that's OK.  I know what the dimensions of
> > the objects are, so I can just correct the perspective in software.
> >
> > Does Gimp have any function like this?  I found the perspective tool,
> > but that requires me to manually shift the perspective and eyeball
> > when I think a rectangular image is produced.  That's not nearly as
> > convenient.
>
> The perspective tool has an inverse mode, if you align the grid lines
> from the wireframe preview with the lines desired to become
> horizontal/vertical and then do the transform you should end up with a
> rectified version of the quadliteral.

Thanks!  That worked.  The size and aspect ratio of the rectified
quadrilateral isn't always close to what I want it to be, though.  Is
there a way to specify this before I do the perspective transform, or
do I just need to do it in 2 steps (correct perspective, and then
re-size)?