% read image
cartman=imread('cartmancop.jpg');

% color ranges have been experimentally determined; since the image is
% fairly dark to begin with, threshold values have been set low, so as to
% brighten the image somewhat.

% iterate over rows
for i=1:size(cartman,1)
    % iterate over columns
    for j=1:size(cartman,2)
        % iterate over colors
        for k=1:3
            if (cartman(i,j,k) < 40)
                cartman(i,j,k) = 0;
            elseif (cartman(i,j,k) < 90)
                cartman(i,j,k) = 85;
            elseif (cartman(i,j,k) < 180)
                cartman(i,j,k) = 170;
            else
                cartman(i,j,k) = 255;
            end
        end
    end
end

% display modified image
image(cartman);