According to the documentation of imfill in MATLAB:
BW2 = imfill(BW,'holes');fills holes in the binary image
BW.
A hole is a set of background pixels that cannot be reached by filling in the background from the edge of the image.
Therefore to get the “holes” pixels, make a call to cvFloodFill with the left corner pixel of the image as a seed. You get the holes by complementing the image obtained in the previous step.
MATLAB Example:
BW = im2bw( imread('coins.png') );
subplot(121), imshow(BW)
% used here as if it was cvFloodFill
holes = imfill(BW, [1 1]); % [1 1] is the starting location point
BW(~holes) = 1; % fill holes
subplot(122), imshow(BW)
