Inverse of a projective transformation doesn't work with imwarp

I have an image, and a general projective2d transformation.

I = imread('cameraman.tif');
imshow(I)
tform = projective2d([0.96119642,-0.44830978,-0.00025835048;0.14598410,1.6215615,6.6809996e-05;1496.0447,1046.4227,1]);
J = imwarp(I,tform);
figure
imshow(J)

I want to apply the inverse of the transformation, to get back to the original image. So I do:

tInv = invert(tform);
K = imwarp (J, tInv);
imshow(K);

Why are the results not consistent? The final image is tilted. How can I fix that?

Thanks

Answer 1

[Ashish Uthama]

Try this:

I = imread('cameraman.tif');
imshow(I)
tform = projective2d([0.96119642,-0.44830978,-0.00025835048;
                      0.14598410,1.6215615,6.6809996e-05;
                     1496.0447,1046.4227,1]);
[J, Jref] = imwarp(I, imref2d(size(I)),tform);
disp(Jref)

figure
imshow(J)
tInv = invert(tform);
K = imwarp (J,Jref, tInv);
imshow(K);

imref2d helps capture the full spatial location of the output image. Notice how the X/YWorldLimits are large numbers? This gets lost when you dont use spatial referencing - hence, in your post, the input you are giving the second imwarp is not strictly the mathematical output of the first imwarp call.

[Matteo Guidi]

Perfect, that was exactly what I was looking for.

Thank you very much!