# How to crop an image A which is a subset of an image B

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dheeraj surabhi on 12 Oct 2015
Commented: dheeraj surabhi on 30 Oct 2015
I have two images where image A is a subset of image B.I could with feature matching technique - identify, match and show the images as a pair. Now that i have identified and matched image A with image B. i want to clip out(crop) that exact region from image B and create a new image. How can i do this, any help is appreciated ?
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### Accepted Answer

Dima Lisin on 13 Oct 2015
Edited: Dima Lisin on 25 Oct 2015
If you have matched the points, then you can simply find the bounding box of the matched points:
points = round(matchedTarget.Location);
left = min(points(:, 1));
right = max(points(:, 1));
top = min(points(:, 2));
bottom = max(points(:, 2));
croppedImage = target(top:bottom, left:right, :);
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dheeraj surabhi on 30 Oct 2015
Thanks Dima. It works.
However i have a problem here. the fact that we are doing round() makes the cropped image loose a slight portion of edges as in the new image that i cropped out would have borders cut down slightly. This is happening since we are rounding the indices i guess, any idea on how can i overcome this and be able to crop the exact image?

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### More Answers (2)

Thorsten on 12 Oct 2015
If I understood correctly, you have found the part in image B that is exactly like image A, and now you want to crop that part of image B. Because both are identical, the cropped image would be exactly like A, so you can just write
C = A;
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Thorsten on 12 Oct 2015
C = B(ind1,ind2,:);
where ind1, ind2 are the vectors ob indices that define the region.

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Image Analyst on 12 Oct 2015
You have said you "have identified and matched image A with image B". If you did that, then you know the coordinates, for example like I did in my attached normxcorr2() demo. So simply use imcrop() after that.
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Image Analyst on 12 Oct 2015
Sorry - I don't have the Computer Vision System Toolbox. Perhaps Dima will answer you.

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