How to change white on the outside to black?

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Accepted Answer

DGM
DGM on 19 May 2022
Some of the objects are connected to the surrounding white blob. You'll need to deal with that. You might be able to do something like:
A = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1004025/image.png');
A = rgb2gray(A)>127; % binarize
B = imopen(A,ones(3)); % try to break connectivity
B = imclearborder(B); % clear border
B = A & ~B; % difference of original and smoothed copy sans border
B = bwareafilt(B,1); % select only the border object, delete speckles
B = A & ~B; % remove border object from original image
imshow(B)
  4 Comments
DGM
DGM on 19 May 2022
As you've probably already figured out, your working image is probably still a single-channel logical image, whereas the attached PNG file is a uint8-scale RGB image. In that case, the conversion and thresholding isn't necessary unless dealing with a copy like the one attached.

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