clear all;

close all;

clc;

img=imread('colorbar.jpg');%('ngc6543a.jpg');

%img=mat2gray(img);  %[0,1];

[m n dim]=size(img);

imshow(img);

%picture RGB

img=double(img);

R=img(:,:,1);

G=img(:,:,2);

B=img(:,:,3);

%%RGB2YCbCr

Y=zeros(m,n);    %

Cb=zeros(m,n);

Cr=zeros(m,n);

matrix=[0.299 0.587 0.114;

        -0.172 -0.339 0.511;

        0.511 -0.428 -0.083];

for i=1:m

   for j=1:n

        tmp=matrix*[R(i,j) G(i,j) B(i,j)]';

        Y(i,j)=tmp(1);

        Cb(i,j)=tmp(2)+128;

        Cr(i,j)=tmp(3)+128;

   end

end

%%YCbCr2RGB

matrix=inv(matrix);

for i=1:m

   for j=1:n

        tmp=matrix*[Y(i,j) Cb(i,j)-128 Cr(i,j)-128]';

        R(i,j)=tmp(1);

        G(i,j)=tmp(2);

        B(i,j)=tmp(3);

   end

end

%%

img(:,:,1)=R;

img(:,:,2)=G;

img(:,:,3)=B;

figure;

imshow(uint8(img))