Try this:
grayImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
grayImage = grayImage(:, :, 1);
end
if max(grayImage(:)) == 1 && length(unique(grayImage(:))) == 2
else
end
You can also use isa(grayImage, 'logical') or similar to identify what class it is.