% cdemo.m
% Demonstrating how to transform from different color coordinates
% (c) copyright 1997-2005 by Yu Hen Hu
% created 9/15/97
% last updated: 9/22/2005
%
clear all
echo on
[x,map]=imread('images/mysail.bmp'); 
    % Matlab represent each image by an index value and a color map
    % associated with that index.  Each row of the color map
    % contains the R,G,B value of that index. If a picture has 256
    % colors, the map will contain at most 256 rows.  
    % For example, x(1,1) = 99, and map(99,:)=[.2784 .2824 .3412];
    % after converting this image to rgb format, r(1,1)=.2784,
    % g(1,1)=.2824, and b(1,1,) = .3412
oldmap=map;
figure(1),imshow(x,map)
pause

% Now let use work only on the first five by five block of the image. 
bsize=input('demostration size = (default: 5) ');
if isempty(bsize), bsize=5; end
yx=x(1:bsize,1:bsize);
bsize2=bsize*bsize;
rgb=ind2rgb(yx,map)
% You may verify [r(1,1) g(1,1) b(1,1)]=map(99,:)!
pause

% Now let us convert the rgb image to YIQ coordinate
% For convenience, we convert the 5 by 5 matrices of r,g,b into 
% row vectors using the command "reshape"

rv=reshape(rgb(:,:,1),1,bsize2); 
gv=reshape(rgb(:,:,2),1,bsize2); 
bv=reshape(rgb(:,:,3),1,bsize2);

% Then construct a 3 by bsize*bsize matrix

v = [rv; gv; bv];

% Next multiply v by the 3 by 3 transformation matrix in 
% eq. 4.6.6 (pp.228 of the text book)

yiq=[.299 .587 .114; .596 -.275 -.321; .212 -.523 .311]*v;

% next convert each row of yiq into bsize by bsize matrices

yi=reshape(yiq(2,:),bsize,bsize); yq=reshape(yiq(3,:),bsize,bsize);
y = reshape(yiq(1,:),bsize,bsize) 
pause

% Now to check y is indeed the intensity, let us use image processing
% tool box command

Igray=rgb2gray(rgb)

% You can verify that y and Igray are the same.

% Our next goal is to convert the rgb colormap to hsi (hsv) colormap
pause

hsv=rgb2hsv(map);  % Hue, Saturation and Value
                   % Hue is actually cos(H) in the text book(?)

% Let us change the saturation values of the color map to 1 and 
% convert it back to rgb

[mh,nh]=size(hsv);
newmap = hsv2rgb([hsv(:,1) ones(mh,1) hsv(:,3)]);

set(gcf,'ColorMap',newmap)
imshow(x)