How can I display registered images on top of one another?

I have registered one image to another using IMTRANSFORM. I would like to display one image on top of the other. How can I specify the spatial location of IMTRANSFORM's output image so that the images can be displayed in one axes, and they will be aligned with one another?

Here is the code that I am attempting to use:

% Load the unregistered image, and make it grayscale.
unreg = imread('westconcordaerial.png'); 
unreg = rgb2gray(unreg);

% Load the registered image.
base = imread('westconcordorthophoto.png'); 

% Display the images.
figure, imshow(base), title('Base image');
figure, imshow(unreg), title('Unregistered image');

% Load the control points, construct the transform, and 
% apply it to the unregistered image..
load westconcordpoints
tform = cp2tform(input_points, base_points, 'projective');
[registered] = imtransform(unreg, tform, 'Fill', 255);

% Display the combined figure.
figure, imshow(registered);
hold on
h = imshow(base);
set(h, 'AlphaData', 0.5);
title('Registered+Base image');

Answer 1

[MathWorks Support Team]

This enhancement has been incorporated in Release 14 Service Pack 2 (R14SP2). For previous product releases, please read below for any possible workarounds:

The reason that the images are not aligned is because the x and y data of the images do not correspond with each other. In other words, the images do not share a common spatial coordinate system.

To correct this, you must explicitly specify the x and y coordinates of the images. The following example shows how to specify these values when you apply the transformation using IMTRANSFORM.

 

% Construct the transform.
tform = cp2tform(input_points, base_points, 'projective');
% Apply the transform, using the IMTRANSFORM syntax that  
% returns the x and y values.
[registered, xdata, ydata] = imtransform(unreg, tform, 'Fill', 255);

% Display the combined figure, specifying the x and y coordinates.
figure, imshow(registered, 'XData', xdata, 'YData', ydata);
hold on
h = imshow(base);
set(h, 'AlphaData', 0.5);
title('Registered+Base image');