Steve Eddins has developed MATLAB and image processing capabilities for MathWorks since 1993. He also coaches development teams on designing programming interfaces for engineers and scientists. Steve coauthored Digital Image Processing Using MATLAB.
I have seen some requests and questions related to identifying objects in a binary image that are touching the image border. Sometimes the question relates to the use of imclearborder, and sometimes the question is about regionprops. Today, I'll show you how to tackle the problem both ways.
I'll be using this binary version of the rice.png sample image from the Image Processing Toolbox.
The function imclearborder removes all objects touching the border.
B = imclearborder(A);
That seems to be the opposite of what we want. We can, however, convert this into the desired result by using the MATLAB element-wise logical operators, such as & (and), | (or), and ~ (not). In words, we want the foreground pixels that are in A and are not in B. As a MATLAB expression, it looks like this:
C = A & ~B;
The function regionprops can compute all sorts of properties of binary image objects. Here is a simple example that computes the area and centroid of each object in our sample image. I'm using the form of regionprops that returns a table.
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