Many thanks for your clarification. It works perfectly fine now.

Regards,
Henry.

I am resizing an image with following two methods:
1) makeform + imtransform
2) imresize

I = imread('pout.tif');
size(I)
sx = 5;
sy = 7;
% using makeform + imtransform
T = [sx 0 0; 0 sy 0; 0 0 1];
tform = maketform('affine', T);
I2 = imtransform(I, tform);
% using imresize
I3 = imresize(I, 'scale', [sx sy]);
size(I2)
size(I3)

When sx or sy is large (says > 2), the first method does not seem to return the correct dimension as 2nd method. Is this a limitation in imtransform? I need the first method for transformation beyond just scale. Appreciated that if you can help to clarify on the matter. Thank you.

Regards,
Henry.

I wonder if I run into the limits of image transformation with the application.

Based on 2 sets of 4 Ctrl points I establish a projective image transformation. (‘cp2tform’)
I transform the image using ‘imtransform’. After some processing of the transformed image, I obtain new ctrl points for further processing. Using the inverse transformation I locate these new ctrl points on the original image (‘tforminv’). I control in and output space using the [xdata,ydata] output from ‘imtransform’.

It all works fine, unless the projective transform reaches a relatively steep perspective angle (~60degrees). Transforming the image works fine but the inverse transformation of the ctrl points has an unexplained offset.

The transformed ctrl points appear in the original image but with a slight error on perspective and location. It looks like the function lost some accuracy. Again the whole process works fine on images with less perspective.

Have you encountered this phenomenon? Any idea what is causing it and better what can be done.

Thanks! Great Blog!