如何从MATLAB中4个角点指定的图像中裁剪一部分

Question

I want to crop only the portion closed by red lines in this image:-

I have the four corner points (x1,y1) , (x2,y2) , (x3,y3) , (x4,y4) . I tried imcrop but that's for rectangular crop. Output image needs to be RGB.

Answer 1

I used google search to find your original image file :-

Now, if I understand your question correctly, this is what you're looking for:

I=imread('nYNKB.jpg');
Isize = size(I);

mask = poly2mask([43 214 227 123],[131 22 112 198],Isize(1,1),Isize(1,2));
% where [x1,x2,x3,x4] = [43 214 227 123] & [y1,y2,y3,y4] = [131 22 112 198]

I_masked = bsxfun(@times,I,cast(mask,class(I)));

subplot(1,2,1)
imshow(I);
title('Original Image')

subplot(1,2,2)
imshow(I_masked)
title('Masked Image')

Output:-

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Edit:-

If you do not want the black background, the closest you can go is with this:

figure(2)
mask = bsxfun(@eq,I_masked,reshape([0 0 0],1,1,3));
image(I_masked,'alphadata',1-double(all(mask,3)));
axis off
title('Masked Image')

Output:-

---

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Alternate Solution (if output does not have to be RGB) :-

I = rgb2gray(imread('nYNKB.jpg'));
imshow(I);
h = imfreehand; 
M = ~h.createMask();
I(M) = 0;
imshow(I);