Histogram equalization, RGB and HSV

Histogram_equalization.m

function [output] = Histogram_equalization(input_image)
%first test the image is a RGB or gray image
hsv = true;
if numel(size(input_image)) == 3
    %this is a RGB image
    %here is just one method, if you have other ways to do the
    %equalization, you can change the following code
    if hsv
        input_image = rgb2hsv(input_image);
        h=input_image(:,:,1);
        s=input_image(:,:,2);
        v=input_image(:,:,3);
        s = zoom_hist(s);
        v = zoom_hist(v);   
        output = cat(3, h, s, v);
        output = hsv2rgb(output);
    else
        r=input_image(:,:,1);
        g=input_image(:,:,2);
        b=input_image(:,:,3);
        r = hist_equal(r);
        g = hist_equal(g);
        b = hist_equal(b);
        output = cat(3,r,g,b);
    end
else
    %this is a gray image
    [output] = hist_equal(input_image);
end
    function ret = zoom_hist(a)
        ret = double(hist_equal(uint8(256 * a))) / 256;
    end
    function [ret] = hist_equal(input_channel)
        % hist of input_channel
        input_channel = input_channel + 1;
        [height, width] = size(input_channel);
        src = get_hist(input_channel);
        %         figure, plot(1:256, src);
        % above: collect and get hist
        % following steps generate the function to realize histeq
        % principle: f(x) = 256 / numel * (\sum_0^x{src_x})
        conversion = zeros(256, 1);
        cur = 0;
        pixels = numel(input_channel);
        for i = 1:256
            cur = cur + src(i);
            conversion(i) = 256 * cur / pixels;
        end
        % above: generate function(0:255) -> pixel value
        ret = zeros(height, width, 'uint8');
        for i = 1:height
            for j = 1:width
                ret(i, j) = conversion(input_channel(i, j));
            end
        end
        %         figure, plot(1:256, get_hist(ret + 1));
        %you should complete this sub-function
    end

    function ret = get_hist(channel)
        ret = zeros(256, 1);
        [height, width] = size(channel);
        for m = 1:height
            for n = 1:width
                ret(channel(m, n)) = ret(channel(m, n)) + 1;
            end
        end
    end

end