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Color Processing

Saturation et desaturation

Method

The desaturation is a uniform reduction of RGB colors. To make it, we weight the difference between a color and the luminance by a factor f. As:

[ R ' G ' B ' ] [ Y Y Y ] + f [ R - Y G - Y B - Y ]

For the desaturation 0 f < 1 , for the saturation 1 < f . An f=0 will give a grayscale image (luminance) and an f=1 doesn't change the original image.

Program

 function desaturation
clear all;
close all;
figure(  'Name','Desaturation Saturation',...
            'NumberTitle','off',...
            'color',[0.3137 0.3137 0.5098]);
       
a(1)=axes('units','normalized',...
    'position',[0.05 0.35 0.45 0.45]);
a(2)=axes('units','normalized',...
    'position',[0.5 0.35 0.45 0.45]);
 
uicontrol(  'style','pushbutton',...
            'string','load',...
            'Position', [10 10 50 20],...
            'callback',@loadimage);
uicontrol(  'style','Slider',...
            'Position', [180 10 100 20],...
            'Min',0,'Max',10,'Value',0.5,...
            'SliderStep',[0.001 0.01], ...
            'callback',@saturation);
       
text(1)=uicontrol(  'style','text',...
            'string','facteur de saturation: 0.5',...
            'Position', [150 30 160 20]);
%parametre initial
setappdata(gcf,'img',1);
setappdata(gcf,'f',0.5);

     
function loadimage(~,~)
    % appeler quand appui check box
    [filename, pathname] = uigetfile({'*.jpg;*.tif;*.png;*.gif;*.bmp','All Image Files';...
          '*.*','All Files' },'mytitle',...
          'C:\Work\myfile.jpg')

    img = double(imread(filename));
    setappdata(1,'img',img);
    axes(a(1))
    imshow(uint8(img))
    title('original image')

   
end
function saturation(hObj,~)
     f = get(hObj,'Value');
     img = getappdata(1,'img');    
     R=img(:,:,1);
     G=img(:,:,2);
     B=img(:,:,3);
     %Luminance
     wr=0.299;
     wg=0.587;
     wb=0.114;
     img_L = ( R * wr + G * wg + B * wb );
     %hueless
     img_hueless = cat(3, img_L, img_L, img_L);
     %saturation
     img_D = img_hueless + f * cat(3, R-img_L, G-img_L, B-img_L);
     axes(a(2))
     imshow(uint8(img_D))
     if f<1
         title('desaturation')
     else
         title('saturation')
     end
     set( text(1), 'String', strcat('facteur de saturation: ',num2str(f)));
end

end

Example

desaturation with f=0.5
desaturation
saturation with f=2
saturation

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