Cropping a particular object in an image

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Aditya 2016-3-30

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回答： Image Analyst 2016-3-30

Hello,

I need to crop a specific object from an image, I have the object annotated and I also have the pixels of the boundaries of the object. Now I want to crop that particular object and nothing else. Please help me out.

Thanks.

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Answer 1

Image Analyst 2016-3-30

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在 MATLAB Online 中打开

You said you " have the pixels of the boundaries of the object", so simply use them as indexes:

croppedImage = originalImage(row1:row2, col1:col2); % Gray scale.
croppedImage = originalImage(row1:row2, col1:col2, :); % If color RGB image.

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Answer 2

Charles Dunn 2016-3-30

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编辑：Charles Dunn 2016-3-30

You might find Point in Polygon algorithms useful: https://en.wikipedia.org/wiki/Point_in_polygon

It would be a lot simpler if the object were guaranteed to be convex, but I doubt that is the case.

Here is a simple-ish method. Do a cumsum() horizontally on the binary boundary image. For any pixels with an odd cumsum value, they are in the shape. Or that binary mask with the boundary pixels, and you'll get a binary mask for your full shape.

There is an edge case where a boundary is horizontal, so your cumsum will run exactly along the boundary. I'm not sure how to handle that case robustly...

There are probably more efficient/robust methods as well.