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dynare/matlab/utilities/graphics/colorspace.m

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function varargout = colorspace(Conversion,varargin)
%COLORSPACE Transform a color image between color representations.
% B = COLORSPACE(S,A) transforms the color representation of image A
% where S is a string specifying the conversion. The input array A
% should be a real full double array of size Mx3 or MxNx3. The output B
% is the same size as A.
%
% S tells the source and destination color spaces, S = 'dest<-src', or
% alternatively, S = 'src->dest'. Supported color spaces are
%
% 'RGB' sRGB IEC 61966-2-1
% 'YCbCr' Luma + Chroma ("digitized" version of Y'PbPr)
% 'JPEG-YCbCr' Luma + Chroma space used in JFIF JPEG
% 'YDbDr' SECAM Y'DbDr Luma + Chroma
% 'YPbPr' Luma (ITU-R BT.601) + Chroma
% 'YUV' NTSC PAL Y'UV Luma + Chroma
% 'YIQ' NTSC Y'IQ Luma + Chroma
% 'HSV' or 'HSB' Hue Saturation Value/Brightness
% 'HSL' or 'HLS' Hue Saturation Luminance
% 'HSI' Hue Saturation Intensity
% 'XYZ' CIE 1931 XYZ
% 'Lab' CIE 1976 L*a*b* (CIELAB)
% 'Luv' CIE L*u*v* (CIELUV)
% 'LCH' CIE L*C*H* (CIELCH)
% 'CAT02 LMS' CIE CAT02 LMS
%
% All conversions assume 2 degree observer and D65 illuminant.
%
% Color space names are case insensitive and spaces are ignored. When
% sRGB is the source or destination, it can be omitted. For example
% 'yuv<-' is short for 'yuv<-rgb'.
%
% For sRGB, the values should be scaled between 0 and 1. Beware that
% transformations generally do not constrain colors to be "in gamut."
% Particularly, transforming from another space to sRGB may obtain
% R'G'B' values outside of the [0,1] range. So the result should be
% clamped to [0,1] before displaying:
% image(min(max(B,0),1)); % Clamp B to [0,1] and display
%
% sRGB (Red Green Blue) is the (ITU-R BT.709 gamma-corrected) standard
% red-green-blue representation of colors used in digital imaging. The
% components should be scaled between 0 and 1. The space can be
% visualized geometrically as a cube.
%
% Y'PbPr, Y'CbCr, Y'DbDr, Y'UV, and Y'IQ are related to sRGB by linear
% transformations. These spaces separate a color into a grayscale
% luminance component Y and two chroma components. The valid ranges of
% the components depends on the space.
%
% HSV (Hue Saturation Value) is related to sRGB by
% H = hexagonal hue angle (0 <= H < 360),
% S = C/V (0 <= S <= 1),
% V = max(R',G',B') (0 <= V <= 1),
% where C = max(R',G',B') - min(R',G',B'). The hue angle H is computed on
% a hexagon. The space is geometrically a hexagonal cone.
%
% HSL (Hue Saturation Lightness) is related to sRGB by
% H = hexagonal hue angle (0 <= H < 360),
% S = C/(1 - |2L-1|) (0 <= S <= 1),
% L = (max(R',G',B') + min(R',G',B'))/2 (0 <= L <= 1),
% where H and C are the same as in HSV. Geometrically, the space is a
% double hexagonal cone.
%
% HSI (Hue Saturation Intensity) is related to sRGB by
% H = polar hue angle (0 <= H < 360),
% S = 1 - min(R',G',B')/I (0 <= S <= 1),
% I = (R'+G'+B')/3 (0 <= I <= 1).
% Unlike HSV and HSL, the hue angle H is computed on a circle rather than
% a hexagon.
%
% CIE XYZ is related to sRGB by inverse gamma correction followed by a
% linear transform. Other CIE color spaces are defined relative to XYZ.
%
% CIE L*a*b*, L*u*v*, and L*C*H* are nonlinear functions of XYZ. The L*
% component is designed to match closely with human perception of
% lightness. The other two components describe the chroma.
%
% CIE CAT02 LMS is the linear transformation of XYZ using the MCAT02
% chromatic adaptation matrix. The space is designed to model the
% response of the three types of cones in the human eye, where L, M, S,
% correspond respectively to red ("long"), green ("medium"), and blue
% ("short").
% Copyright (C) 2005-2010 Pascal Getreuer
% Copyright (C) 2017 Dynare Team
%
% Redistribution and use in source and binary forms, with or without
% modification, are permitted provided that the following conditions are
% met:
%
% * Redistributions of source code must retain the above copyright
% notice, this list of conditions and the following disclaimer.
% * Redistributions in binary form must reproduce the above copyright
% notice, this list of conditions and the following disclaimer in
% the documentation and/or other materials provided with the distribution
%
% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
% AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
% IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
% ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
% LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
% CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
% SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
% INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
% CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
% ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
% POSSIBILITY OF SUCH DAMAGE.
%%% Input parsing %%%
if nargin < 2, error('Not enough input arguments.'); end
[SrcSpace,DestSpace] = parse(Conversion);
if nargin == 2
Image = varargin{1};
elseif nargin >= 3
Image = cat(3,varargin{:});
else
error('Invalid number of input arguments.');
end
FlipDims = (size(Image,3) == 1);
if FlipDims, Image = permute(Image,[1,3,2]); end
if ~isa(Image,'double'), Image = double(Image)/255; end
if size(Image,3) ~= 3, error('Invalid input size.'); end
SrcT = gettransform(SrcSpace);
DestT = gettransform(DestSpace);
if ~ischar(SrcT) && ~ischar(DestT)
% Both source and destination transforms are affine, so they
% can be composed into one affine operation
T = [DestT(:,1:3)*SrcT(:,1:3),DestT(:,1:3)*SrcT(:,4)+DestT(:,4)];
Temp = zeros(size(Image));
Temp(:,:,1) = T(1)*Image(:,:,1) + T(4)*Image(:,:,2) + T(7)*Image(:,:,3) + T(10);
Temp(:,:,2) = T(2)*Image(:,:,1) + T(5)*Image(:,:,2) + T(8)*Image(:,:,3) + T(11);
Temp(:,:,3) = T(3)*Image(:,:,1) + T(6)*Image(:,:,2) + T(9)*Image(:,:,3) + T(12);
Image = Temp;
elseif ~ischar(DestT)
Image = rgb(Image,SrcSpace);
Temp = zeros(size(Image));
Temp(:,:,1) = DestT(1)*Image(:,:,1) + DestT(4)*Image(:,:,2) + DestT(7)*Image(:,:,3) + DestT(10);
Temp(:,:,2) = DestT(2)*Image(:,:,1) + DestT(5)*Image(:,:,2) + DestT(8)*Image(:,:,3) + DestT(11);
Temp(:,:,3) = DestT(3)*Image(:,:,1) + DestT(6)*Image(:,:,2) + DestT(9)*Image(:,:,3) + DestT(12);
Image = Temp;
else
Image = feval(DestT,Image,SrcSpace);
end
%%% Output format %%%
if nargout > 1
varargout = {Image(:,:,1),Image(:,:,2),Image(:,:,3)};
else
if FlipDims, Image = permute(Image,[1,3,2]); end
varargout = {Image};
end
return
function [SrcSpace,DestSpace] = parse(Str)
% Parse conversion argument
if ischar(Str)
Str = lower(strrep(strrep(Str,'-',''),'=',''));
k = find(Str == '>');
if length(k) == 1 % Interpret the form 'src->dest'
SrcSpace = Str(1:k-1);
DestSpace = Str(k+1:end);
else
k = find(Str == '<');
if length(k) == 1 % Interpret the form 'dest<-src'
DestSpace = Str(1:k-1);
SrcSpace = Str(k+1:end);
else
error(['Invalid conversion, ''',Str,'''.']);
end
end
SrcSpace = alias(SrcSpace);
DestSpace = alias(DestSpace);
else
SrcSpace = 1; % No source pre-transform
DestSpace = Conversion;
if any(size(Conversion) ~= 3), error('Transformation matrix must be 3x3.'); end
end
return
function Space = alias(Space)
Space = strrep(strrep(Space,'cie',''),' ','');
if isempty(Space)
Space = 'rgb';
end
switch Space
case {'ycbcr','ycc'}
Space = 'ycbcr';
case {'hsv','hsb'}
Space = 'hsv';
case {'hsl','hsi','hls'}
Space = 'hsl';
case {'rgb','yuv','yiq','ydbdr','ycbcr','jpegycbcr','xyz','lab','luv','lch'}
return
end
return
function T = gettransform(Space)
% Get a colorspace transform: either a matrix describing an affine transform,
% or a string referring to a conversion subroutine
switch Space
case 'ypbpr'
T = [0.299,0.587,0.114,0;-0.1687367,-0.331264,0.5,0;0.5,-0.418688,-0.081312,0];
case 'yuv'
% sRGB to NTSC/PAL YUV
% Wikipedia: http://en.wikipedia.org/wiki/YUV
T = [0.299,0.587,0.114,0;-0.147,-0.289,0.436,0;0.615,-0.515,-0.100,0];
case 'ydbdr'
% sRGB to SECAM YDbDr
% Wikipedia: http://en.wikipedia.org/wiki/YDbDr
T = [0.299,0.587,0.114,0;-0.450,-0.883,1.333,0;-1.333,1.116,0.217,0];
case 'yiq'
% sRGB in [0,1] to NTSC YIQ in [0,1];[-0.595716,0.595716];[-0.522591,0.522591];
% Wikipedia: http://en.wikipedia.org/wiki/YIQ
T = [0.299,0.587,0.114,0;0.595716,-0.274453,-0.321263,0;0.211456,-0.522591,0.311135,0];
case 'ycbcr'
% sRGB (range [0,1]) to ITU-R BRT.601 (CCIR 601) Y'CbCr
% Wikipedia: http://en.wikipedia.org/wiki/YCbCr
% Poynton, Equation 3, scaling of R'G'B to Y'PbPr conversion
T = [65.481,128.553,24.966,16;-37.797,-74.203,112.0,128;112.0,-93.786,-18.214,128];
case 'jpegycbcr'
% Wikipedia: http://en.wikipedia.org/wiki/YCbCr
T = [0.299,0.587,0.114,0;-0.168736,-0.331264,0.5,0.5;0.5,-0.418688,-0.081312,0.5]*255;
case {'rgb','xyz','hsv','hsl','lab','luv','lch','cat02lms'}
T = Space;
otherwise
error(['Unknown color space, ''',Space,'''.']);
end
return
function Image = rgb(Image,SrcSpace)
% Convert to sRGB from 'SrcSpace'
switch SrcSpace
case 'rgb'
return
case 'hsv'
% Convert HSV to sRGB
Image = huetorgb((1 - Image(:,:,2)).*Image(:,:,3),Image(:,:,3),Image(:,:,1));
case 'hsl'
% Convert HSL to sRGB
L = Image(:,:,3);
Delta = Image(:,:,2).*min(L,1-L);
Image = huetorgb(L-Delta,L+Delta,Image(:,:,1));
case {'xyz','lab','luv','lch','cat02lms'}
% Convert to CIE XYZ
Image = xyz(Image,SrcSpace);
% Convert XYZ to RGB
T = [3.2406, -1.5372, -0.4986; -0.9689, 1.8758, 0.0415; 0.0557, -0.2040, 1.057];
R = T(1)*Image(:,:,1) + T(4)*Image(:,:,2) + T(7)*Image(:,:,3); % R
G = T(2)*Image(:,:,1) + T(5)*Image(:,:,2) + T(8)*Image(:,:,3); % G
B = T(3)*Image(:,:,1) + T(6)*Image(:,:,2) + T(9)*Image(:,:,3); % B
% Desaturate and rescale to constrain resulting RGB values to [0,1]
AddWhite = -min(min(min(R,G),B),0);
R = R + AddWhite;
G = G + AddWhite;
B = B + AddWhite;
% Apply gamma correction to convert linear RGB to sRGB
Image(:,:,1) = gammacorrection(R); % R'
Image(:,:,2) = gammacorrection(G); % G'
Image(:,:,3) = gammacorrection(B); % B'
otherwise % Conversion is through an affine transform
T = gettransform(SrcSpace);
temp = inv(T(:,1:3));
T = [temp,-temp*T(:,4)];
R = T(1)*Image(:,:,1) + T(4)*Image(:,:,2) + T(7)*Image(:,:,3) + T(10);
G = T(2)*Image(:,:,1) + T(5)*Image(:,:,2) + T(8)*Image(:,:,3) + T(11);
B = T(3)*Image(:,:,1) + T(6)*Image(:,:,2) + T(9)*Image(:,:,3) + T(12);
Image(:,:,1) = R;
Image(:,:,2) = G;
Image(:,:,3) = B;
end
% Clip to [0,1]
Image = min(max(Image,0),1);
return
function Image = xyz(Image,SrcSpace)
% Convert to CIE XYZ from 'SrcSpace'
WhitePoint = [0.950456,1,1.088754];
switch SrcSpace
case 'xyz'
return
case 'luv'
% Convert CIE L*uv to XYZ
WhitePointU = (4*WhitePoint(1))./(WhitePoint(1) + 15*WhitePoint(2) + 3*WhitePoint(3));
WhitePointV = (9*WhitePoint(2))./(WhitePoint(1) + 15*WhitePoint(2) + 3*WhitePoint(3));
L = Image(:,:,1);
Y = (L + 16)/116;
Y = invf(Y)*WhitePoint(2);
U = Image(:,:,2)./(13*L + 1e-6*(L==0)) + WhitePointU;
V = Image(:,:,3)./(13*L + 1e-6*(L==0)) + WhitePointV;
Image(:,:,1) = -(9*Y.*U)./((U-4).*V - U.*V); % X
Image(:,:,2) = Y; % Y
Image(:,:,3) = (9*Y - (15*V.*Y) - (V.*Image(:,:,1)))./(3*V); % Z
case {'lab','lch'}
Image = lab(Image,SrcSpace);
% Convert CIE L*ab to XYZ
fY = (Image(:,:,1) + 16)/116;
fX = fY + Image(:,:,2)/500;
fZ = fY - Image(:,:,3)/200;
Image(:,:,1) = WhitePoint(1)*invf(fX); % X
Image(:,:,2) = WhitePoint(2)*invf(fY); % Y
Image(:,:,3) = WhitePoint(3)*invf(fZ); % Z
case 'cat02lms'
% Convert CAT02 LMS to XYZ
T = inv([0.7328, 0.4296, -0.1624;-0.7036, 1.6975, 0.0061; 0.0030, 0.0136, 0.9834]);
L = Image(:,:,1);
M = Image(:,:,2);
S = Image(:,:,3);
Image(:,:,1) = T(1)*L + T(4)*M + T(7)*S; % X
Image(:,:,2) = T(2)*L + T(5)*M + T(8)*S; % Y
Image(:,:,3) = T(3)*L + T(6)*M + T(9)*S; % Z
otherwise % Convert from some gamma-corrected space
% Convert to sRGB
Image = rgb(Image,SrcSpace);
% Undo gamma correction
R = invgammacorrection(Image(:,:,1));
G = invgammacorrection(Image(:,:,2));
B = invgammacorrection(Image(:,:,3));
% Convert RGB to XYZ
T = inv([3.2406, -1.5372, -0.4986; -0.9689, 1.8758, 0.0415; 0.0557, -0.2040, 1.057]);
Image(:,:,1) = T(1)*R + T(4)*G + T(7)*B; % X
Image(:,:,2) = T(2)*R + T(5)*G + T(8)*B; % Y
Image(:,:,3) = T(3)*R + T(6)*G + T(9)*B; % Z
end
return
function Image = hsv(Image,SrcSpace)
% Convert to HSV
Image = rgb(Image,SrcSpace);
V = max(Image,[],3);
S = (V - min(Image,[],3))./(V + (V == 0));
Image(:,:,1) = rgbtohue(Image);
Image(:,:,2) = S;
Image(:,:,3) = V;
return
function Image = hsl(Image,SrcSpace)
% Convert to HSL
switch SrcSpace
case 'hsv'
% Convert HSV to HSL
MaxVal = Image(:,:,3);
MinVal = (1 - Image(:,:,2)).*MaxVal;
L = 0.5*(MaxVal + MinVal);
temp = min(L,1-L);
Image(:,:,2) = 0.5*(MaxVal - MinVal)./(temp + (temp == 0));
Image(:,:,3) = L;
otherwise
Image = rgb(Image,SrcSpace); % Convert to sRGB
% Convert sRGB to HSL
MinVal = min(Image,[],3);
MaxVal = max(Image,[],3);
L = 0.5*(MaxVal + MinVal);
temp = min(L,1-L);
S = 0.5*(MaxVal - MinVal)./(temp + (temp == 0));
Image(:,:,1) = rgbtohue(Image);
Image(:,:,2) = S;
Image(:,:,3) = L;
end
return
function Image = lab(Image,SrcSpace)
% Convert to CIE L*a*b* (CIELAB)
WhitePoint = [0.950456,1,1.088754];
switch SrcSpace
case 'lab'
return
case 'lch'
% Convert CIE L*CH to CIE L*ab
C = Image(:,:,2);
Image(:,:,2) = cos(Image(:,:,3)*pi/180).*C; % a*
Image(:,:,3) = sin(Image(:,:,3)*pi/180).*C; % b*
otherwise
Image = xyz(Image,SrcSpace); % Convert to XYZ
% Convert XYZ to CIE L*a*b*
X = Image(:,:,1)/WhitePoint(1);
Y = Image(:,:,2)/WhitePoint(2);
Z = Image(:,:,3)/WhitePoint(3);
fX = f(X);
fY = f(Y);
fZ = f(Z);
Image(:,:,1) = 116*fY - 16; % L*
Image(:,:,2) = 500*(fX - fY); % a*
Image(:,:,3) = 200*(fY - fZ); % b*
end
return
function Image = luv(Image,SrcSpace)
% Convert to CIE L*u*v* (CIELUV)
WhitePoint = [0.950456,1,1.088754];
WhitePointU = (4*WhitePoint(1))./(WhitePoint(1) + 15*WhitePoint(2) + 3*WhitePoint(3));
WhitePointV = (9*WhitePoint(2))./(WhitePoint(1) + 15*WhitePoint(2) + 3*WhitePoint(3));
Image = xyz(Image,SrcSpace); % Convert to XYZ
Denom = Image(:,:,1) + 15*Image(:,:,2) + 3*Image(:,:,3);
U = (4*Image(:,:,1))./(Denom + (Denom == 0));
V = (9*Image(:,:,2))./(Denom + (Denom == 0));
Y = Image(:,:,2)/WhitePoint(2);
L = 116*f(Y) - 16;
Image(:,:,1) = L; % L*
Image(:,:,2) = 13*L.*(U - WhitePointU); % u*
Image(:,:,3) = 13*L.*(V - WhitePointV); % v*
return
function Image = lch(Image,SrcSpace)
% Convert to CIE L*ch
Image = lab(Image,SrcSpace); % Convert to CIE L*ab
H = atan2(Image(:,:,3),Image(:,:,2));
H = H*180/pi + 360*(H < 0);
Image(:,:,2) = sqrt(Image(:,:,2).^2 + Image(:,:,3).^2); % C
Image(:,:,3) = H; % H
return
function Image = cat02lms(Image,SrcSpace)
% Convert to CAT02 LMS
Image = xyz(Image,SrcSpace);
T = [0.7328, 0.4296, -0.1624;-0.7036, 1.6975, 0.0061; 0.0030, 0.0136, 0.9834];
X = Image(:,:,1);
Y = Image(:,:,2);
Z = Image(:,:,3);
Image(:,:,1) = T(1)*X + T(4)*Y + T(7)*Z; % L
Image(:,:,2) = T(2)*X + T(5)*Y + T(8)*Z; % M
Image(:,:,3) = T(3)*X + T(6)*Y + T(9)*Z; % S
return
function Image = huetorgb(m0,m2,H)
% Convert HSV or HSL hue to RGB
N = size(H);
H = min(max(H(:),0),360)/60;
m0 = m0(:);
m2 = m2(:);
F = H - round(H/2)*2;
M = [m0, m0 + (m2-m0).*abs(F), m2];
Num = length(m0);
j = [2 1 0;1 2 0;0 2 1;0 1 2;1 0 2;2 0 1;2 1 0]*Num;
k = floor(H) + 1;
Image = reshape([M(j(k,1)+(1:Num).'),M(j(k,2)+(1:Num).'),M(j(k,3)+(1:Num).')],[N,3]);
return
function H = rgbtohue(Image)
% Convert RGB to HSV or HSL hue
[M,i] = sort(Image,3);
i = i(:,:,3);
Delta = M(:,:,3) - M(:,:,1);
Delta = Delta + (Delta == 0);
R = Image(:,:,1);
G = Image(:,:,2);
B = Image(:,:,3);
H = zeros(size(R));
k = (i == 1);
H(k) = (G(k) - B(k))./Delta(k);
k = (i == 2);
H(k) = 2 + (B(k) - R(k))./Delta(k);
k = (i == 3);
H(k) = 4 + (R(k) - G(k))./Delta(k);
H = 60*H + 360*(H < 0);
H(Delta == 0) = nan;
return
function Rp = gammacorrection(R)
Rp = zeros(size(R));
i = (R <= 0.0031306684425005883);
Rp(i) = 12.92*R(i);
Rp(~i) = real(1.055*R(~i).^0.416666666666666667 - 0.055);
return
function R = invgammacorrection(Rp)
R = zeros(size(Rp));
i = (Rp <= 0.0404482362771076);
R(i) = Rp(i)/12.92;
R(~i) = real(((Rp(~i) + 0.055)/1.055).^2.4);
return
function fY = f(Y)
fY = real(Y.^(1/3));
i = (Y < 0.008856);
fY(i) = Y(i)*(841/108) + (4/29);
return
function Y = invf(fY)
Y = fY.^3;
i = (Y < 0.008856);
Y(i) = (fY(i) - 4/29)*(108/841);
return
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