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From: eddy on 7 Jun 2010 14:04
Hi

I have difficulties getting around matlab, so I would appreciate any help.

Problem:
On the attached images as it can be seen there is a geometric transformation, induced by 'affine' cp2tform function. Now I would need to restore the images. There is a third image as a clue for how the transformation was initially made.The size of the images before transformation was 640x427.

It seems to me that a vector has to be calculated from the third image and applied to the other images? Or do I need to set up nodes and how?

http://img249.imageshack.us/i/71893695.png/
http://img196.imageshack.us/i/14127371.png/
http://img685.imageshack.us/i/cp2tform.jpg/
From: ImageAnalyst on 7 Jun 2010 18:23
Since you know the exact points (the four corners and the middle) I'd
probably use maketform() and tformfwd(). Just pass in the 5 actual
(distorted) points and the desired location of the 5 points to
maketform() to get the transform. Then use tformfwd(), passing in the
transform and the bad image to "fix up" the bad image to make it look
like the desired image.
From: eddy on 7 Jun 2010 15:23
Hm, thank You very much. I have tried something similar, but it seems that I am doing it wrong. In the help I have found this:

"T = maketform('affine',U,X) builds a TFORM struct T for a two-dimensional affine transformation that maps each row of U to the corresponding row of X. The U and X arguments are each 3-by-2 and define the corners of input and output triangles. The corners cannot be collinear."

So I write:
tform=maketform('affine',[1 1; 256.5 256.5; 1 512], [1 1; 200.5 150.5; 1 427]); % the first matrix for the upper triangle of the distorted image, the second matrix for the same triangle of the image I want.
Where do I ad the other three triangles os what am I doing wrong?
From: ImageAnalyst on 7 Jun 2010 21:57
I don't know - maybe I'm wrong. I used the quadrilateral version so I
had four points that needed to be mapped. But maybe you can try the
'custom' option and just list your points (5 of them) all separated by
semi colons between each x,y pair, just like you did for the
triangles. Otherwise you might have to have 4 transforms - one for
each triangle.
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