Is it possible to erode only the outermost layer of a circle?

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Teshan Rezel
Teshan Rezel 2022-5-31
评论： Teshan Rezel 2022-6-2
Hi folks,
I am looking to erode a circle from the outside in, layer by layer. So far, I have tried to use the following:
x = imerode(x, strel('disk', 1));
but in the case of an image with a higher Euler number than 1, this erodes the holes within the image as well...Is there a way around this please?
img1, img2, img3
  2 个评论
Teshan Rezel
Teshan Rezel 2022-5-31
@Walter Roberson Unfortunately, the holes are an important part of this exercise. Essentially, I'm trying to model a physical process where something is "eaten" from the outside in (this is the nearest analogy I can find, apologies if it doesn't make sense!)

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采纳的回答

Image Analyst
Image Analyst 2022-5-31
Another option would be to use bwperim and imfill. Something like (untested)
% Fill holes
mask2 = imfill(mask, 'holes');
% Get outer perimeter.
perimImage = bwperim(mask2);
% Set those pixels to false/0/black.
mask(perimImage) = false;

更多回答（2 个）

Image Analyst
Image Analyst 2022-5-31
Here are the steps I'd try, assuming you're starting with a binary image
Call bwboundaries to get the outer layer. Of course, tell it to ignore interior holes - there's an option for that.
Have a for loop where you visit every (x,y) location and set it's value to false.
Something like (untested)
boundaries = bwboundaries(mask, 4, 'noholes');
bxy = boundaries{1};
rows = bxy(:, 1);
cols = bxy(:, 2);
for k = 1 : length(rows)
mask(row, col) = false;
end
Walter Roberson
Walter Roberson 2022-5-31
negate the image so the holes and background are true and the white is false. bwareafilt requesting the largest. That will be the background. negate the background to get the filled foreground. Subtract the original image from the filled one to get the location of the holes. Erode the filled image. Subtract the holes.
You might have to filter differently if you have multiple disconnected objects.

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