100 lines
3.1 KiB
C++
100 lines
3.1 KiB
C++
////////////////////////////////////////////////////////////////
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//
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// Gamut mapping algorithm
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//
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// copyright (c) 2010-2011 Emil Martinec <ejmartin@uchicago.edu>
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//
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//
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// code dated: February 2, 2011
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//
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// sRGBgamutbdy.cc is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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//
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////////////////////////////////////////////////////////////////
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//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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#define SQR(x) ((x)*(x))
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#define D50x 0.96422
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#define D50z 0.82521
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#define u0 4.0*D50x/(D50x+15+3*D50z)
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#define v0 9.0/(D50x+15+3*D50z)
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#define sgn(x) (x<0 ? -1 : 1)
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#define sqrt2 (sqrt(2))
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#define sqrt3 (sqrt(3))
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#define sqrt6 (sqrt(6))
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#define K 20
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#define rmax (3*K + 1)
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#define rctr (2*K)
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#define cctr (2*K + 1)
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#define maxindx (2*(3*K+1) + SQR(3*K+1))
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// solutions to scaling u and v to XYZ paralleliped boundaries
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/* some equations:
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fu(X,Y,Z) = 4 X/(X + 15 Y + 3 Z);
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fv(X,Y,Z) = 9 Y/(X + 15 Y + 3 Z);
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take the plane spanned by X=a*Xr+b*Xg+c*Xb etc with one of a,b,c equal to 0 or 1,
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and itersect with the line u0+lam*u, or in other words solve
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u0+lam*u=fu(X,Y,Z)
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v0+lam*v=fv(X,Y,Z)
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the value of lam is the scale factor that takes the color to the gamut boundary
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*/
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// columns of the matrix p=xyz_rgb are RGB tristimulus primaries in XYZ
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// c is the color fixed on the boundary; and m=0 for c=0, m=1 for c=255
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void ImProcFunctions::gamutmap(float &X, float &Y, float &Z, const double p[3][3])
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{
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float u = 4*X/(X+15*Y+3*Z)-u0;
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float v = 9*Y/(X+15*Y+3*Z)-v0;
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float lam[3][2];
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float lam_min = 1.0;
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for (int c=0; c<3; c++)
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for (int m=0; m<2; m++) {
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int c1=(c+1)%3;
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int c2=(c+2)%3;
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lam[c][m] = (-(p[0][c1]*p[1][c]*((-12 + 3*u0 + 20*v0)*Y + 4*m*65535*v0*p[2][c2])) + \
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p[0][c]*p[1][c1]*((-12 + 3*u0 + 20*v0)*Y + 4*m*65535*v0*p[2][c2]) - \
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4*v0*p[0][c1]*(Y - m*65535*p[1][c2])*p[2][c] + 4*v0*p[0][c]*(Y - m*65535*p[1][c2])*p[2][c1] - \
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(4*m*65535*v0*p[0][c2] - 9*u0*Y)*(p[1][c1]*p[2][c] - p[1][c]*p[2][c1]));
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lam[c][m] /= (3*u*Y*(p[0][c1]*p[1][c] - p[1][c1]*(p[0][c] + 3*p[2][c]) + 3*p[1][c]*p[2][c1]) + \
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4*v*(p[0][c1]*(5*Y*p[1][c] + m*65535*p[1][c]*p[2][c2] + Y*p[2][c] - m*65535*p[1][c2]*p[2][c]) - \
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p[0][c]*(5*Y*p[1][c1] + m*65535*p[1][c1]*p[2][c2] + Y*p[2][c1] - m*65535*p[1][c2]*p[2][c1]) + \
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m*65535*p[0][c2]*(p[1][c1]*p[2][c] - p[1][c]*p[2][c1])));
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if (lam[c][m]<lam_min && lam[c][m]>0) lam_min=lam[c][m];
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}
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u = u*lam_min + u0;
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v = v*lam_min + v0;
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X = (9*u*Y)/(4*v);
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Z = (12 - 3*u - 20*v)*Y/(4*v);
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}
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//};//namespace
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