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Color Processing

Color Space RGB To HVS

For next compute we use:

I max = max ( R , G , B ) ,
I min = min ( R , G , B ) ,

RGB To HVS

H = { 0 ,  if  I max = I min ( 60 × g - b I max - I min ) m o d ( 360 ) ,  if  I max = r 60 × b - r I max - I min + 120 ,  if  I max = g 60 × r - g I max - I min + 240 ,  if  I max = b }
S = { 0  if  I max = 0 1 - I max I min  if  o t h e r w i s e }
V = I max

HVS To RGB

H ' = ⌊ H 60 ⌋ m o d ( 6 )
f = H 60 - H '
l = V × ( 1 - S )
m = V × ( 1 - f × S )
m = V × ( 1 - ( 1 - f ) × S )
( R , G , B ) = { ( v , n , l )  if  H ' = 0 ( m , v , l )  if  H ' = 1 ( l , v , n )  if  H ' = 2 ( l , m , v )  if  H ' = 3 ( n , l , v )  if  H ' = 4 ( v , l , m )  if  H ' = 5 }

Program

clear all;
close all;

[filename, pathname] = uigetfile({'*.jpg;*.tif;*.png;*.gif;*.bmp','All Image Files';...
          '*.*','All Files' },'mytitle',...
          'C:\Work\myfile.jpg');

img = imread(filename);
[ligne colonne dimension]=size(img);
img=double(img);
R=img(:,:,1);
G=img(:,:,2);
B=img(:,:,3);

% rgb to HSV
H=zeros(ligne,colonne);
S=zeros(ligne,colonne);
V=zeros(ligne,colonne);
for l = 1 : ligne
    for c =  1: colonne
        Imax = max(max([R(l,c) G(l,c) B(l,c)]));
        Imin = min(min([R(l,c) G(l,c) B(l,c)]));
       
        if Imax == Imin
            ;
        elseif Imax == R(l,c)
            H(l,c) = mod((60 * (G(l,c) - B(l,c)) / (Imax-Imin) + 360) , 360);
        elseif Imax == G(l,c)
            H(l,c) = 60 * (B(l,c) - R(l,c)) / (Imax-Imin) + 120;  
        elseif Imax == B(l,c)
            H(l,c) = 60 * (R(l,c) - G(l,c)) / (Imax-Imin) + 240;      
        end
       
        if Imax ~= 0
            S(l,c) = 1 - (Imin/Imax);
        end
       
        V(l,c)= Imax;
           
    end
end


Rp=zeros(ligne,colonne);
Gp=zeros(ligne,colonne);
Bp=zeros(ligne,colonne);
for i = 1 : ligne
    for j =  1: colonne
         v=V(i,j);
         h = mod(floor(H(i,j)/60),6);
         f = H(i,j)/60 - h;
         l = v*(1-S(i,j));
         m = v*(1-f*S(i,j));
         n = v*(1-(1-f)*S(i,j));
         if h == 0
             Rp(i,j)=v; Gp(i,j)= n; Bp(i,j)= l;
         elseif h == 1
             Rp(i,j)=m; Gp(i,j)= v; Bp(i,j)= l;
         elseif h == 2
             Rp(i,j)=l; Gp(i,j)= v; Bp(i,j)= n;
         elseif h == 3
             Rp(i,j)=l; Gp(i,j)= m; Bp(i,j)= v;
         elseif h == 4
             Rp(i,j)=n; Gp(i,j)= l; Bp(i,j)= v;
         elseif h == 5
             Rp(i,j)=v; Gp(i,j)= l; Bp(i,j)= m;
         end
             
    end
end



figure(  'Name','RGB --> HSV --> RGB',...
            'NumberTitle','off',...
            'color',[0.3137 0.3137 0.5098]);
vide=zeros(ligne,colonne);
subplot(4,3,1)
imshow(uint8(cat(3,R,G,B)))
title('Image origine')
subplot(4,3,4)
imshow(uint8(cat(3,R,vide,vide)))
title('Image R origine')
subplot(4,3,7)
imshow(uint8(cat(3,vide,G,vide)))
title('Image G origine')
subplot(4,3,10)
imshow(uint8(cat(3,vide,vide,B)))
title('Image B origine')

 
 subplot(4,3,5)
imagesc(H,[min(min(H)) max(max(H))])
colormap('gray')
axis image
title('Image H')
subplot(4,3,8)
imagesc(S,[min(min(S)) max(max(S))])
colormap('gray')
axis image
title('Image S')
subplot(4,3,11)
imagesc(V,[min(min(V)) max(max(V))])
colormap('gray')
axis image
title('Image V')

 subplot(4,3,3)
imshow(uint8(cat(3,Rp,Gp,Bp)))
title('Image reconstuite')
 subplot(4,3,6)
imshow(uint8(cat(3,Rp,vide,vide)))
title('Image R reconstuite')
subplot(4,3,9)
imshow(uint8(cat(3,vide,Gp,vide)))
title('Image G reconstuite')
subplot(4,3,12)
imshow(uint8(cat(3,vide,vide,Bp)))
title('Image B reconstuite')

Example

Color space RGB to HLS

RGB TO HLS


rgbtohsv

H ' = { u n d e f i n e d  if  I max = I min G - B I max - I min m o d ( 6 )  if  I max = R B - R I max - I min + 2  if  I max = G R - G I max - I min + 4  if  I max = B }
H = 60 × H '
L = 1 2 ( I max + I min )
S = { 0  if  I max = I min I max - I min 1 - | 2 L - 1 |  if  o t h e r w i s e }

HLS To RGB

C = V × S
H ' = H 60
X = C ( 1 - | H ' m o d ( 2 ) - 1 | )
( R ' , G ' , B ' ) = { ( 0,0 ,0 )  if  H = u n d e f i n e d ( C , X ,0 )  if  ⌊ H ⌋ = 0 ( X , C ,0 )  if  ⌊ H ⌋ = 1 ( 0 , C , X )  if  ⌊ H ⌋ = 2 ( 0 , X , C )  if  ⌊ H ⌋ = 3 ( X ,0 , C )  if  ⌊ H ⌋ = 4 ( C ,0 , X )  if  ⌊ H ⌋ = 5 }
m = V - C
( R , G , B ) = ( R ' + m , G ' + m , B ' + m )

Program

 clear all;
close all;

[filename, pathname] = uigetfile({'*.jpg;*.tif;*.png;*.gif;*.bmp','All Image Files';...
          '*.*','All Files' },'mytitle',...
          'C:\Work\myfile.jpg');

img = imread(filename);
[ligne colonne dimension]=size(img);
img=double(img);
R=img(:,:,1);
G=img(:,:,2);
B=img(:,:,3);
 % rgb to HLS
R=R/255;
G=G/255;
B=B/255;
H=zeros(ligne,colonne);
L=zeros(ligne,colonne);
S=zeros(ligne,colonne);
for l = 1 : ligne
    for c =  1: colonne
        Imax = max(max([R(l,c) G(l,c) B(l,c)]));
        Imin = min(min([R(l,c) G(l,c) B(l,c)]));
        C = Imax - Imin;
       
        if C == 0
            H(l,c) = NaN;
        elseif Imax == R(l,c)
            H(l,c) = mod(((G(l,c) - B(l,c)) / (C)),6);
        elseif Imax == G(l,c)
            H(l,c) = (B(l,c) - R(l,c)) / (C) + 2;  
        elseif Imax == B(l,c)
            H(l,c) = (R(l,c) - G(l,c)) / (C) + 4;      
        end
       
        L(l,c)= 0.5*(Imax+Imin);
       
        if C ~= 0
            S(l,c) = C / (1-abs(2*L(l,c)-1));
        end
   
    end
end
H=H*60;

Rp=zeros(ligne,colonne);
Gp=zeros(ligne,colonne);
Bp=zeros(ligne,colonne);
Hp=H/60;
for i = 1 : ligne
    for j =  1: colonne
         C=(1-abs(2*L(i,j)-1))* S(i,j);
         h=Hp(i,j);
         X=C*(1-abs(mod(h,2)-1));  
         h=floor(Hp(i,j));
         if  isnan(h)
             Rp(i,j)=0; Gp(i,j)= 0; Bp(i,j)= 0;
         elseif h == 0
             Rp(i,j)=C; Gp(i,j)= X; Bp(i,j)= 0;
         elseif h == 1
             Rp(i,j)=X; Gp(i,j)= C; Bp(i,j)= 0;
         elseif h == 2
             Rp(i,j)=0; Gp(i,j)= C; Bp(i,j)= X;
         elseif h == 3
             Rp(i,j)=0; Gp(i,j)= X; Bp(i,j)= C;
         elseif h == 4
             Rp(i,j)=X; Gp(i,j)= 0; Bp(i,j)= C;
         elseif h == 5
             Rp(i,j)=C; Gp(i,j)= 0; Bp(i,j)= X;
         end
         
         Imin = L(i,j)-0.5 * C;
         Rp(i,j)= Rp(i,j)+Imin;
         Gp(i,j)= Gp(i,j)+Imin;
         Bp(i,j)= Bp(i,j)+Imin;
             
    end
end
R=R*255;
G=G*255;
B=B*255;
Rp=Rp*255;
Gp=Gp*255;
Bp=Bp*255;
figure(  'Name','RGB --> HSL --> RGB',...
            'NumberTitle','off',...
            'color',[0.3137 0.3137 0.5098]);
vide=zeros(ligne,colonne);
subplot(4,3,1)
imshow(uint8(cat(3,R,G,B)))
title('Image origine')
subplot(4,3,4)
imshow(uint8(cat(3,R,vide,vide)))
title('Image R origine')
subplot(4,3,7)
imshow(uint8(cat(3,vide,G,vide)))
title('Image G origine')
subplot(4,3,10)
imshow(uint8(cat(3,vide,vide,B)))
title('Image B origine')

 
 subplot(4,3,5)
imagesc(H,[min(min(H)) max(max(H))])
colormap('gray')
axis image
title('Image H')
subplot(4,3,8)
imagesc(S,[min(min(S)) max(max(S))])
colormap('gray')
axis image
title('Image S')
subplot(4,3,11)
imagesc(V,[min(min(V)) max(max(V))])
colormap('gray')
axis image
title('Image V')

 subplot(4,3,3)
imshow(uint8(cat(3,Rp,Gp,Bp)))
title('Image reconstuite')
 subplot(4,3,6)
imshow(uint8(cat(3,Rp,vide,vide)))
title('Image R reconstuite')
subplot(4,3,9)
imshow(uint8(cat(3,vide,Gp,vide)))
title('Image G reconstuite')
subplot(4,3,12)
imshow(uint8(cat(3,vide,vide,Bp)))
title('Image B reconstuite')

Example


rgbtohsl


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