Excluding Perimeter values of Boundary using regionprops

Hi.

I have an image that I create a binary image from with an aim to use this as a mask to read values of the foreground on the original image.

I use the following code to obtain the regions that I then mask back onto the raw image and take the mean of them.

      labeledImage = bwlabel(Binary, 8);     % Label each blob so we can make measurements of it
      blobMeasurements = regionprops(labeledImage, ROI, 'all');     %ROI is original image
      numberOfBlobs = size(blobMeasurements, 1);
      hold on;
      boundaries = bwboundaries(Binary);  
      numberOfBoundaries = size(boundaries);
      subplot(4,5,[3,4,8,9])
      hold on
      for k = 1 : numberOfBoundaries
    thisBoundary = boundaries{k};
    plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 1);
      end
      hold off;

      %Get mean intensity of foreground by blobmeasurements
      allBlobIntensities = [blobMeasurements.MeanIntensity]
      meanI=mean(allBlobIntensities(:))

My question is, I want to exclude the values that are say within 1 pixel of the actual region boundary (for all boundaries, i.e exclude the perimeter of each boundary.

Is this possible? Thanks Jason

Answer 1

[Image Analyst]

Contract your mask by calling imerode() before you label it:

Binary = imerode(Binary, true(3));

[Jason]

Thanks, what does the 3 mean? Jason

[Image Analyst]

It makes a 3 by 3 array of "true" values, meaning that it takes into consideration all 9 values in that little square window as it scans the image, finding the min value, which will be zero/false/black. So it has the effect of eating/dissolving a layer from your binary image, essentially shrinking it by one pixel all around.