% FILTER_REMOVE_COLOR(VIDEO, MODE) removes the color information of the current

% frame (video.frame(1).filtered). MODE can be either BW (function returns an RGB

% image where only intensity values are considered) or SEPIA ( function returns

% an RGB image transformed into a yellow-brownish image).

%  

%   VIDEO:  a structure containing an array of frames where frame(1)

%   contains the most current frame. 

% 

%   VIDEO = FILTER_REMOVE_COLOR(VIDEO, MODE) returns the original video structure

%   with the updated current video.frame(1).filtered. Each filter takes

%   video.frame(1).filtered as input and writes the result back to this array.

%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%

%   IMPLEMENTATION:

%       bw: We switch to the HSV color space and set the saturation to 0.

%       So no color has enough saturation to differ from gray.

%       sepia: We multiply the RGB values of each pixel with a sepia

%       matrix.

%

%   PHYSICAL BACKGROUND:

%       In the twenties there were no colors in films.

%       A color with no saturation is black, gray or white.

%       When a photograph is 60 years and older, the black color turns into

%       brown and white into yellow because of the UV radiation. This color

%       space is called sepia.

%       The sepia matrix multiplication transforms the color of the frame.

function [video] = filter_remove_color(video, mode)    



    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    % Black / White Mode

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    if (strcmp(mode,'bw'))                

        video.frame(1).filtered = black_white(video.frame(1).filtered);

        return;

    end





    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    % Sepia Mode

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    if (strcmp(mode,'sepia'))

        video.frame(1).filtered = sepia(video.frame(1).filtered);

        return;

    end



    disp_error('Only ''bw'' and ''sepia'' mode supported!');









    %%

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    % REMOVE COLOUR INFORMATION FROM AN RGB IMAGE

    %

    % 1) CONVERT img FROM RGB TO YCbCr COLORSPACE

    % 2) SET CHROMA CHANNELS APPROPRIATELY (NEUTRAL CHROMA CHANNELS)

    % 3) CONVERT IMAGE BACK TO RGB

    % 4) RETURN 

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    function [bw] = black_white(img)

        img = rgb2hsv(img);

        img(:,:,2) = 0;

        bw = hsv2rgb(img);

    end

    %%    

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    % CONVERT RGB IMAGE TO SEPIA

    %

    % 1) USE SEPIA CONVERSION MATRIX FOR CONVERTING RGB IMAGE img TO SEPIA

    % 2) RETURN CONVERTED IMAGE 

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    function [sepia] = sepia(img)

        sepia_matrix = [0.4 0.769 0.189; 0.349 0.686 0.168; 0.272 0.534 0.131];

        sepia = img;

%         for x=1:size(img,1)

%             for y =1:size(img,2)

%                 sepia(x,y,:)= sepia_matrix * reshape(img(x,y,:), 3,1);

%             end

%         end

        sepia(:,:,1) = img(:,:,1)*sepia_matrix(1,1)+ img(:,:,2)*sepia_matrix(1,2)+ img(:,:,3)*sepia_matrix(1,3);

        sepia(:,:,2) = img(:,:,1)*sepia_matrix(2,1)+ img(:,:,2)*sepia_matrix(2,2)+ img(:,:,3)*sepia_matrix(2,3);

        sepia(:,:,3) = img(:,:,1)*sepia_matrix(3,1)+ img(:,:,2)*sepia_matrix(3,2)+ img(:,:,3)*sepia_matrix(3,3);

    end

end