Shearing results different between using "imtransform" and "tformarray"

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caoccw
caoccw on 30 Mar 2014
Commented: aa on 23 Oct 2014
Hi, guys. Recently I want to conduct a shearing transform on a 4D object, and I found "tformarray" function seemed to be a good choice. Since I never used that function before, and to verify also to learn it, I tesed the same image using "imtransform" and "tformarray" respectively. But I received different results: "tformarray" result had a slight shift position compared to the one produced by "imtransform". I was wondering if "tformarray" needed some "prior transforms" to yield the same result as the "imtransform".
And my code has been listed as following. You can see what did I get. Please read and make a reply. Thank you.
clc;close all;clear all;
% original picture generalization
I = checkerboard(40,1,1);
sizeI = size(I);
figure; imshow(I,'InitialMagnification','fit')
title('original picture');
% shearing
alpha = 0.9;
B = [1/alpha 1-1/alpha 0; 0 1 0; 0 0 1];
xform = B;
% using imtransform
T1 = maketform('affine',B);
J = imtransform(I,T1);
figure; imshow(J,'InitialMagnification','fit');
title('imtransform');
% using tformarray
T2 = maketform('affine',xform);
R = makeresampler('cubic','circular');
fill = 0.3;
J1 = tformarray(I,T2,R,[2 1],[2 1], [89, 89], [], fill);
figure; imshow(J1,'InitialMagnification','fit');
title('tformarray');
  1 Comment
aa
aa on 23 Oct 2014
Hey! Did u find out what was happening? I am using tformarray and my results are also slightly shifted...But I don't know why. I guess the problem comes from the matrix of the transformation, that is T2 in your example...Do you have any idea of how to fix it? Thanks

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