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

[Liam R E Quin <liam holoweb net>]

On Mon, 2013-02-04 at 00:46 -0800, Elmer Wix wrote:
>  The size and aspect ratio of the rectified
> quadrilateral isn't always close to what I want it to be, though. 

I use it like this when I can:
1. crop the image so the object is in the middle, approximately (or
float it to a new layer together with enough of the surrounding image to
contain the result easily)

2. use "corrective (reverse)" mode with the grid

3. align the grid with a vertical one the left side, half-way doen.

4. move the top *and* the bottom of the grid by the same amount, but in
opposite directions.

5. Now repeat for the right-hand side.

6. Do the top of the image, again using a half-way point, and being
careful to move the corner points diagonally in a line with the
adjustments you already did!

7. Finally do the bottom - this is the most important edge usually, for
the human eye, to think something is level, so do it last.

This way the image doesn't grow huge or shrink to be tiny.

If you get it wrong, you have to undo and start over. I've spent half an
hour or more doing this on some images.

Liam

-- 
Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
Pictures from old books: http://fromoldbooks.org/
Ankh: irc.sorcery.net irc.gnome.org freenode/#xml