I am trying to understand the output of imregcorr and could use some help. Below is the code I am working with. I have my own function called RegisterViaReddy that uses the technique explained in the reference of imregcorr to register images that differ in translation and rotation (I wrote my code before imregcorr was released). Unfortunately I cannot post RegisterViaReddy, but I understand its behavior so hopefully its details are not relevant.
%%Start with a clean workspace clear all;close all;clc;%#ok %%Load image fixedFull = double(imread('cameraman.tif')); rows = 30:226; cols = rows; fixed = fixedFull(rows,cols); %%Specify motion parameters theta = 5;%degrees rowshift = 1.65;%pixels colshift = 5.32;%pixels %%Create rotated/translated image RT = @(img,colshift,rowshift,theta) imrotate( imtransform(img, maketform('affine', [1 0 0; 0 1 0; colshift rowshift 1]), 'bilinear', 'XData', [1 size(img,2)], 'YData', [1 size(img,1)], 'FillValues', 0),theta,'crop'); %#ok movingFull = RT(fixedFull, colshift, rowshift, theta); moving = movingFull(rows,cols); %%Show both images figure; imshowpair(moving,fixed,'montage'); %%Register images [rowshift1, colshift1, theta1, imgReg] = RegisterViaReddy(fixed, moving); tform1 = imregcorr(moving, fixed, 'rigid');
The function handle RT first translates an image and then rotates it. The resulting image is the same size as the input image. The outputs of my own RegisterViaReddy function are
>> [rowshift1, colshift1, theta1] ans = -1.7600 -5.1000 -5.3402
These are nearly the opposites of the known rowshift, colshift, and theta parameters. I wrote my code this way so that
RT(moving,colshift1,rowshift1,theta1);
generates something that looks like the fixed image.
I do not understand how to get these parameters from the output of imregcorr (tform1). I understand that acosd(tform1.T(1,1)) is 5.1799 and is hence the rotation angle. However, tform1.T is
0.9959 0.0903 0 -0.0903 0.9959 0 4.1423 -10.3337 1.0000
How do I extract meaningful translation parameters from this? I know I can generate something that looks like the fixed image using
imwarp(moving, tform1);
but the resulting array is 214x214 whereas fixed and moving are 197x197. Is there any way to get the translation offsets that I input from the output of imregcorr?
NOTE:-
% Define a pure transformation, apply this transformation to input point (w,z) = (0,0) tx = 1.65; ty = 5.32; T = [1 0 0; 0 1 0; tx ty 1]; w = 0; z = 0; xy = [w z 1]*T
This means that for a rigid transformation, the tform object returned by imregcorr is off the form:
tform = [cos(theta) sin(theta) 0; sin(theta) -cos(theta) 0; tx ty 1];
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