function [M,ColorP] = change_color_mode(M,dir,options)
% change_color_mode - change of color representation
%
% M = change_color_mode(M,dir,options);
%
% switch between RGB and another color mode.
%
% options.color_mode can be:
% 'rgb' (no change), 'hsv', 'ycbcr', 'pca'
%
% For PCA you should proceed like this:
% [Mg,options.ColorP] = change_color_mode(M0,+1,options);
% M1 = change_color_mode(Mg,-1,options);
%
% Copyright (c) 2007 Gabriel Peyre
options.null = 0;
color_mode = getoptions(options, 'color_mode', 'hsv');
if strcmp(color_mode,'rgb')
return;
end
n = size(M,1);
if size(M,3)~=3
error('Works only for color images');
end
if strcmp(color_mode, 'pca')
nsamples = min(8000,n^2);
if not(isfield(options, 'ColorP'))
if dir==-1
error('You must provide options.ColorP');
end
if nargout==1
error('Output argument ColorP Missing');
end
% compute PCA components
Ma = reshape(M,n^2,3);
sel = randperm(n^2); sel = sel(1:nsamples);
[Y,X1,v,Psi] = pca( Ma(sel,:)',3);
ColorP = cat(2, Y, Psi(:));
else
ColorP = options.ColorP;
end
if dir==1
M = reshape(M,n^2,3)';
M = ColorP(:,1:3)'*(M - repmat(ColorP(:,4), 1,n^2));
M = reshape(M',n,n,3);
else
M = reshape(M,n^2,3)';
M = ColorP(:,1:3)*M + repmat(ColorP(:,4), 1,n^2);
M = reshape(M',n,n,3);
end
return;
end
warning off;
if dir==1
M = feval( ['rgb2' color_mode], M);
end
if strcmp(color_mode, 'hsv')
M = M(:,:,3:-1:1);
end
if dir==-1
M = feval( [color_mode '2rgb'], M);
end
warning on;
function out = rgb2ycbcr(in)
%RGB2YCBCR Convert RGB values to YCBCR color space.
% YCBCRMAP = RGB2YCBCR(MAP) converts the RGB values in MAP to
% the YCBCR color space. YCBCRMAP is a M-by-3 matrix that contains
% the YCBCR luminance (Y) and chrominance (Cb and Cr) color values as
% columns. Each row represents the equivalent color to the
% corresponding row in the RGB colormap.
%
% YCBCR = RGB2YCBCR(RGB) converts the truecolor image RGB to the
% equivalent image in the YCBCR color space.
%
% Class Support
% -------------
% If the input is an RGB image, it can be of class uint8, uint16,
% or double; the output image is of the same class as the input
% image. If the input is a colormap, the input and output colormaps
% are both of class double.
%
% Examples
% --------
% Convert RGB image to YCbCr.
%
% RGB = imread('board.tif');
% YCBCR = rgb2ycbcr(RGB);
%
% Convert RGB color space to YCbCr.
%
% map = jet(256);
% newmap = rgb2ycbcr(map);
% See also NTSC2RGB, RGB2NTSC, YCBCR2RGB.
% Copyright 1993-2003 The MathWorks, Inc.
% $Revision: 1.13.4.2 $ $Date: 2003/08/23 05:54:37 $
% Reference:
% C.A. Poynton, "A Technical Introduction to Digital Video", John Wiley
% & Sons, Inc., 1996, p. 175
%initialize variables
isColormap = false;
classin = class(in);
%must reshape colormap to be m x n x 3 for transformation
if (ndims(in)==2)
%colormap
isColormap=true;
colors = size(in,1);
in = reshape(in, [colors 1 3]);
end
% set up constants for transformation
T = [65.481 128.553 24.966;...
-37.797 -74.203 112; ...
112 -93.786 -18.214];
offset = [16;128;128];
offset16 = 257 * offset;
fac8 = 1/255;
fac16 = 257/65535;
%initialize output
out = in;
% do transformation
switch classin
case 'uint8'
for p=1:3
out(:,:,p) = imlincomb(T(p,1)*fac8,in(:,:,1),T(p,2)*fac8,in(:,:,2),...
T(p,3)*fac8,in(:,:,3),offset(p));
end
case 'uint16'
for p=1:3
out(:,:,p) = imlincomb(T(p,1)*fac16,in(:,:,1),T(p,2)*fac16,in(:,:,2),...
T(p,3)*fac16,in(:,:,3),offset16(p));
end
case 'double'
% These equations transform RGB in [0,1] to YCBCR in [0, 255]
for p=1:3
out(:,:,p) = T(p,1) * in(:,:,1) + T(p,2) * in(:,:,2) + T(p,3) * ...
in(:,:,3) + offset(p);
end
out = out / 255;
end
if isColormap
out = reshape(out, [colors 3 1]);
end
function rgb = ycbcr2rgb(in)
%YCBCR2RGB Convert YCbCr values to RGB color space.
% RGBMAP = YCBCR2RGB(YCBCRMAP) converts the YCbCr values in the
% colormap YCBCRMAP to the RGB color space. If YCBCRMAP is M-by-3 and
% contains the YCbCr luminance (Y) and chrominance (Cb and Cr) color
% values as columns, then RGBMAP is an M-by-3 matrix that contains
% the red, green, and blue values equivalent to those colors.
%
% RGB = YCBCR2RGB(YCBCR) converts the YCbCr image to the equivalent
% truecolor image RGB.
%
% Class Support
% -------------
% If the input is a YCbCr image, it can be of class uint8, uint16,
% or double; the output image is of the same class as the input
% image. If the input is a colormap, the input and output
% colormaps are both of class double.
%
% Example
% -------
% Convert image from RGB space to YCbCr space and back.
%
% rgb = imread('board.tif');
% ycbcr = rgb2ycbcr(rgb);
% rgb2 = ycbcr2rgb(ycbcr);
%
% See also NTSC2RGB, RGB2NTSC, RGB2YCBCR.
% Copyright 1993-2003 The MathWorks, Inc.
% $Revision: 1.15.4.2 $ $Date: 2003/08/23 05:54:51 $
% Reference:
% Charles A. Poynton, "A Technical Introduction to Digital Video",
% John Wiley & Sons, Inc., 1996
%initialize variables
isColormap = false;
classin = class(in);
%must reshape colormap to be m x n x 3 for transformation
if (ndims(in)==2)
%colormap
isColormap=true;
colors = size(in,1);
in = reshape(in, [colors 1 3]);
end
%initialize output
rgb = in;
% set up constants for transformation. T alone will transform YCBCR in [0,255]
% to RGB in [0,1]. We must scale T and the offsets to get RGB in the appropriate
% range for uint8 and for uint16 arrays.
T = [65.481 128.553 24.966;...
-37.797 -74.203 112; ...
112 -93.786 -18.214];
Tinv = T^-1;
offset = [16;128;128];
Td = 255 * Tinv;
offsetd = Tinv * offset;
T8 = Td;
offset8 = T8 * offset;
T16 = (65535/257) * Tinv;
offset16 = 65535 * Tinv * offset;
switch classin
case 'double'
for p = 1:3
rgb(:,:,p) = Td(p,1) * in(:,:,1) + Td(p,2) * in(:,:,2) + ...
Td(p,3) * in(:,:,3) - offsetd(p);
end
case 'uint8'
for p = 1:3
rgb(:,:,p) = imlincomb(T8(p,1),in(:,:,1),T8(p,2),in(:,:,2), ...
T8(p,3),in(:,:,3),-offset8(p));
end
case 'uint16'
for p = 1:3
rgb(:,:,p) = imlincomb(T16(p,1),in(:,:,1),T16(p,2),in(:,:,2), ...
T16(p,3),in(:,:,3),-offset16(p));
end
end
if isColormap
rgb = reshape(rgb, [colors 3 1]);
end
if isa(rgb,'double')
rgb = min(max(rgb,0.0),1.0);
end
%%%
%Parse Inputs
%%%
function X = parse_inputs(varargin)
checknargin(1,1,nargin,mfilename);
X = varargin{1};
if ndims(X)==2
checkinput(X,{'uint8','uint16','double'},'real nonempty',mfilename,'MAP',1);
if (size(X,2) ~=3 || size(X,1) < 1)
eid = sprintf('Images:%s:invalidSizeForColormap',mfilename);
msg = 'MAP must be a m x 3 array.';
error(eid,'%s',msg);
end
elseif ndims(X)==3
checkinput(X,{'uint8','uint16','double'},'real',mfilename,'RGB',1);
if (size(X,3) ~=3)
eid = sprintf('Images:%s:invalidTruecolorImage',mfilename);
msg = 'RGB must a m x n x 3 array.';
error(eid,'%s',msg);
end
else
eid = sprintf('Images:%s:invalidInputSize',mfilename);
msg = ['RGB2GRAY only accepts two-dimensional or three-dimensional ' ...
'inputs.'];
error(eid,'%s',msg);
end
