Split image using a predefined line

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Is there anyway to split an image into two using a predefined line that passes through an object's centroid. I have already found the centroid and plotted the line, but I am unsure of how to separate the image using this line. Many Thanks
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Matt J
Matt J on 2 May 2014
Edited: Matt J on 2 May 2014
Split it into two what? You mean you want a version of the image with the pixels to one side of the line made dark? How would you like to deal with boundary pixels that lie partially on both sides of the line?
Ben
Ben on 2 May 2014
Edited: Image Analyst on 2 May 2014
I have drawn this line, and i wish to separate the image so i can calculate the height and width of both the bottom and top sections. The image doesn't need to be physically separated, just recognised as two different objects

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Accepted Answer

Image Analyst
Image Analyst on 2 May 2014
Sure. I'm going to assume the line cuts across the entire image. Then use poly2mask() to create a binary image.
mask = poly2mask(x, y);
Then you can either blacken above/below the line.
imageAbove = grayImage;
imageAbove(mask) = 0;
imageBelow = grayImage;
imageBelow(~mask) = 0;
You can also crop to the bounding box or leave it at the original size, using imcrop() or regular indexing.
  5 Comments
Ben
Ben on 3 May 2014
Edited: Ben on 3 May 2014
I have a line drawn throught the cetnroid, but i do not know how to stop the line when it reaches the image border. Edit: I only have Matlab 2012 - if that changes anything
Image Analyst
Image Analyst on 3 May 2014
Ben, it's just simple algebra. I simply used the point slope formula for a line. See attached test3.m file to produce the image below.

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