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How do I remove/replace border pixels from my image?

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burges
burges on 19 Dec 2016
Commented: burges on 20 Dec 2016
I am new to Matlab and will need some help. I have a segmented image in which I would want to remove background (or black) pixels (with value == 1) from the image borders. I have been able to obtain an image mask of the border pixels that I do not want. The interior_blackPixels are useful, but I want to get rid of the outer_blackPixels. The code so far is shown below:
img = [1 1 1 1 1 1 1 1
1 1 1 1 2 2 2 1
1 1 1 2 2 2 2 1
1 1 1 2 2 2 2 1
1 1 2 2 2 2 2 1
1 1 2 2 2 2 2 1
1 3 3 1 1 1 3 1
1 3 3 1 1 1 3 1
1 3 3 3 3 3 3 1
1 1 1 1 1 1 1 1];
% Get the black pixels image array
blackPixels = (img == 1);
% Obtain the other pixels by negating the black pixels
otherPixels = ~blackPixels
% Get the border black pixels (or mask)
outer_blackPixels = blackPixels & ~imclearborder(blackPixels)
interior_blackPixels = blackPixels & ~outer_blackPixels
Please note that I do not mind replacing the pixel values of the outer_blackPixels to ‘0’ as this will not affect my analysis. Hence, I would expect my final image to be something like this:
% set all the border pixels to zeros
new_borderValues = img(outer_blackPixels) == 0
img = [0 0 0 0 0 0 0 0
0 0 0 0 2 2 2 0
0 0 0 2 2 2 2 0
0 0 0 2 2 2 2 0
0 0 2 2 2 2 2 0
0 0 2 2 2 2 2 0
0 3 3 1 1 1 3 0
0 3 3 1 1 1 3 0
0 3 3 3 3 3 3 0
0 0 0 0 0 0 0 0];
The main challenge for me however is that I am not sure how to retrieve the final image wit the black pixel borders replaced (as shown above) using the mask (outer_blackPixels) that I have. Any help/suggestions would be appreciated. Thanks!

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Accepted Answer

Massimo Zanetti
Massimo Zanetti on 19 Dec 2016
You basically don't need your interior_blackPixels. Indeed, your expected image is obtained by simply setting outer_blackPixels of img to 0. Try this:
img(outer_blackPixels)=0
Is this what you need?

  1 Comment

burges
burges on 20 Dec 2016
Oh that works perfectly. I also realized that adding the following lines should work as well.
% logical pixels of interest
A = otherPixels | interior_blackPixels
% new image
newimg = img .*A
In any case, yours is straightforward and simple. Many thanks!

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