How to crop a square that has a rotational angle?

Asked by Guilherme Pelegrini on 9 Mar 2017

Latest activity Commented on by Selina on 1 Apr 2019

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I need to crop one square of this image:

As you can see, I can't use imcrop() because it isn't horizontal, the squares has a rotational angle, and the region cropped need to be precisely on the edge of the line.

How can I do it?

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Answer by Massimo Zanetti on 9 Mar 2017

Edited by Massimo Zanetti on 9 Mar 2017

Inspect this: roipoly

Here is an example of what you can do:

%open an image
A = imread('coins.png');
%run roi tool, where you can define your polygon
BW = roipoly(A);
%extract image pixels in the roi
S = regionprops(BW,'ConvexImage','BoundingBox');
r = S.BoundingBox;
Q = A( round(r(2)) + (1:r(4)) , round(r(1)) + (1:r(3)) );
%display cropped image
im = imagesc(Q);
im.AlphaData = S.ConvexImage;
axis image; colormap gray;

In the roipoly window track your points manually to define a polygon, as in the picture:

Then, right-click and "Create Mask", you will get your cropped image:

1 Comment

Selina on 1 Apr 2019

Hi,

Is it possible to use rectangle crop using the ROI function? If so, can anyone please send a sample coding?

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Guilherme Pelegrini (view profile)