clear all;
close all;

rgb             = imread('lena.bmp');
rgb             = single(rgb);

[row col dim]   = size(rgb);
set(gcf, "position", [50 50 600 600]);
set(gca, "position", [0.07 -0.07 1 1]);
imshow(rgb/256);

tic
ycbcr           = rgb2ycbcr(rgb);
toc
y               = ycbcr(:,:,1);
cb              = ycbcr(:,:,2);
cr              = ycbcr(:,:,3);

yn              = round(y   + 20*randn(row, col));
cbn             = round(cb  + 20*randn(row, col));
crn             = round(cr  + 20*randn(row, col));

yn(find(yn < 0)) = 0;
yn(find(yn > 255)) = 255;
cbn(find(yn < 0)) = 0;
cbn(find(yn > 255)) = 255;
crn(find(yn < 0)) = 0;
crn(find(yn > 255)) = 255;

ycbcr_n = cat(3, yn, cbn, crn);
tic
rgb_n   = ycbcr2rgb(ycbcr_n);
toc

figure;
set(gcf, "position", [50 50 600 600]);
set(gca, "position", [0.07 -0.07 1 1]);
imshow(rgb_n/256);