How to automatically crop empty space (with known color) around an image object (like "-trim" in ImageMagick)?

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Günter Bachelier 2017-1-16

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回答： Jordan Ross 2017-1-24

After a distortion of an image the transformed image can have boarders with a color that was specified with 'FillValues'. I want to automatically crop the image object in the middle i.e. to get rid of the possible asymmetric boarders. Is there a function in Matlab or in the Image Processing Tools?

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Answer 1

Jordan Ross 2017-1-24

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Hello,

One possible solution would be to get the region of interest by color using the "roicolor" function. http://www.mathworks.com/help/images/ref/roicolor.html

Then using that function you can determine the indices of the image without that color. However, please note that this assumes that this color only appears in the border and not inside the image. For example, consider the following script where I remove the outer white box from an image:

I = imread('sampleImage.png');
I = rgb2gray(I);
colorOfInterest = 255;
roi = ~roicolor(I, colorOfInterest, colorOfInterest);
idx = find(roi==1);
[y, x] = ind2sub(size(I), idx);
x1 =  round(min(x));
y1 =  round(min(y));
x2 =  round(max(x));
y2 =  round(max(y));
croppedImage = I(y1:y2, x1:x2);
figure;
subplot(1,2,1);
imshow(I);
subplot(1,2,2);
imshow(croppedImage);