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function YCbCr = rgb2jpeg(RGB)
%-*- texinfo -*-
%@deftypefn {Function} rgb2jpeg
%@verbatim
%RGB2JPEG Coverts from RGB format to the YCbCr format used by JPEG
% Usage: YCbCr = rgb2jpeg(RGB);
%
% Input parameters:
% RGB : 3d data-cube, containing RGB information of the image
%
% Output parameters:
% YCbCr : 3d data-cube, containing the YCbCr information of the
% image
%
% 'rgb2jpeg(RGB)' performs a transformation of the 3d data-cube RGB with
% dimensions N xM x3, which contains information of the
% colours "red", "green" and "blue". The output variable YCbCr is a 3d
% data-cube of the same size containing information about "luminance",
% "chrominance blue" and "chrominance red". The output will be of
% the uint8 type.
%
% See http://en.wikipedia.org/wiki/YCbCr and
% http://de.wikipedia.org/wiki/JPEG.
%
% Examples:
% ---------
%
% In the following example, the Lichtenstein test image is split into
% its three components. The very first subplot is the original image:
%
% f=lichtenstein;
%
% f_jpeg=rgb2jpeg(f);
%
% subplot(2,2,1);
% image(f);axis('image');
%
% Ymono=zeros(512,512,3,'uint8');
% Ymono(:,:,1)=f_jpeg(:,:,1);
% Ymono(:,:,2:3)=128;
% fmono=jpeg2rgb(Ymono);
% subplot(2,2,2);
% image(fmono);axis('image');
%
% Cbmono=zeros(512,512,3,'uint8');
% Cbmono(:,:,2)=f_jpeg(:,:,2);
% Cbmono(:,:,3)=128;
% fmono=jpeg2rgb(Cbmono);
% subplot(2,2,3);
% image(fmono);axis('image');
%
% Crmono=zeros(512,512,3,'uint8');
% Crmono(:,:,3)=f_jpeg(:,:,3);
% Crmono(:,:,2)=128;
% fmono=jpeg2rgb(Crmono);
% subplot(2,2,4);
% image(fmono);axis('image');
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/sigproc/rgb2jpeg.html}
%@seealso{jpeg2rgb}
%@end deftypefn
% Copyright (C) 2005-2016 Peter L. Soendergaard <peter@sonderport.dk>.
% This file is part of LTFAT version 2.3.1
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program. If not, see <http://www.gnu.org/licenses/>.
% AUTHOR: Markus Faulhuber, February 2013
[s1,s2,s3] = size(RGB);
RGB = double(RGB);
if s3 ~= 3
disp('Sorry, this routine is for RGB of dimension NxMx3 only')
return;
end
YCbCr(:,:,1) = 0.299*RGB(:,:,1)+0.587*RGB(:,:,2)+0.114*RGB(:,:,3);
YCbCr(:,:,2) = 128-0.168736*RGB(:,:,1)-0.331264*RGB(:,:,2)+0.5*RGB(:,:,3);
YCbCr(:,:,3) = 128+0.5*RGB(:,:,1)-0.418688*RGB(:,:,2)-0.081312*RGB(:,:,3);
YCbCr = uint8(YCbCr);
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