How to change white on the outside to black?

Answer 1

[DGM]

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)

[Keane Athallah]

Error in Code (line 10)

A = rgb2gray(BW)>127; % binarize

Thank you for your answer, but i have some difficulty to combine it with my code, do you have any solution?

[Keane Athallah]

Error using rgb2gray>parse_inputs (line 79)

MAP must be a m x 3 array. Use im2gray for RGB and grayscale images.

Error in rgb2gray (line 51)

isRGB = parse_inputs(X);

Error in Code (line 15)

A = rgb2gray(L)>127; % binarize

this is the full error that i get!

[Keane Athallah]

i already deal with that error, Thank you so much

[DGM]

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.