How do I shift the alignment of one image over the other?

I have two images (both are of crosses as in x. They were of different sizes and different colours, I converted both of them into binary images and brought the actual crosses (That is,the area of the cross, not the entire image wit whitespace and all) to the same scale. When I use imshowpair to subtract the two images, however, I get a very large answer because the two crosses are not aligned properly over each other. Reference : https://twitter.com/SamyuktaRamnath/status/355657777277968385/photo/1

So, I have two options. Either I just find their centres and align them, or I run an algorithm to find the difference between the two pictures and shift the alignment to the least difference, after shifting it.

But I don't know how to shift the second picture over the first. Any function, or any way that I can move it coordinate by coordinate?

Answer 1

[Image Analyst]

First figure out the overlap region, then place it on a new canvass:

% Create blank new canvass the same size as the reference image.
newCanvass = zeros(size(referenceImage), 'uint8');
% Place overlap image down at row, column
newCanvass(row:end, column:end) = overlapImage;

[Samyukta Ramnath]

Can you explain exactly what you mean by 'figure out the overlap'? And I understand I am to make a blank canvas of the same size as the smaller image. Also, what is row and column here? My overlapImage would be the larger one?

[Image Analyst]

Like say when the images are overlapped perfectly, the upper left corner of image 2 lands at row = 143, and column = 73 (or whatever). Pixels inside the overlap rectangle overlap acceptably while those outside the overlap region exist in either one image or the other but not both.

[Stelios Fanourakis]

@Image Analyst. I want to do something similar. I have 15 dicom images. They are slightly shifted. Need to properly align them to a reference image.