color all pixels in an image black except white pixels

Hi! From the attached .png figure [rxcx3] I would like to keep only the white pixels and turn all other pixels to black. How can I do?

Answer 1

[DGM]

Presuming that "white" is [255 255 255] within the context of a uint8 RGB image:

inpict = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1280620/example_1.png');
inpict = im2gray(inpict);

mk = inpict == 255;

imshow(mk)