/* Our main loop.
*/
void
imb_Lab2LCh( float *p, float *q, int n )
{
int x;
for( x = 0; x < n; x++ ) {
float L = p[0];
float a = p[1];
float b = p[2];
float C, h;
p += 3;
C = sqrt( a * a + b * b );
h = im_col_ab2h( a, b );
q[0] = L;
q[1] = C;
q[2] = h;
q += 3;
}
}
/**
* im_col_dE00:
* @L1: Input coordinate 1
* @a1: Input coordinate 1
* @b1: Input coordinate 1
* @L2: Input coordinate 2
* @a2: Input coordinate 2
* @b2: Input coordinate 2
*
* CIEDE2000, from:
*
* Luo, Cui, Rigg, "The Development of the CIE 2000 Colour-Difference
* Formula: CIEDE2000", COLOR research and application, pp 340
*
* Returns: CIE dE2000 colour difference.
*/
float
im_col_dE00( float L1, float a1, float b1,
float L2, float a2, float b2 )
{
/* Code if you want XYZ params and the colour temp used in the reference
float
im_col_dE00( float X1, float Y1, float Z1,
float X2, float Y2, float Z2 )
{
const double X0 = 94.811;
const double Y0 = 100.0;
const double Z0 = 107.304;
#define f(I) ((I) > 0.008856 ? \
cbrt( (I), 1.0 / 3.0 ) : 7.7871 * (I) + (16.0 / 116.0))
double nX1 = f( X1 / X0 );
double nY1 = f( Y1 / Y0 );
double nZ1 = f( Z1 / Z0 );
double L1 = 116 * nY1 - 16;
double a1 = 500 * (nX1 - nY1);
double b1 = 200 * (nY1 - nZ1);
double nX2 = f( X2 / X0 );
double nY2 = f( Y2 / Y0 );
double nZ2 = f( Z2 / Z0 );
double L2 = 116 * nY2 - 16;
double a2 = 500 * (nX2 - nY2);
double b2 = 200 * (nY2 - nZ2);
*/
/* Chroma and mean chroma (C bar)
*/
double C1 = sqrt( a1 * a1 + b1 * b1 );
double C2 = sqrt( a2 * a2 + b2 * b2 );
double Cb = (C1 + C2) / 2;
/* G
*/
double Cb7 = Cb * Cb * Cb * Cb * Cb * Cb * Cb;
double G = 0.5 * (1 - sqrt( Cb7 / (Cb7 + pow( 25, 7 )) ));
/* L', a', b', C', h'
*/
double L1d = L1;
double a1d = (1 + G) * a1;
double b1d = b1;
double C1d = sqrt( a1d * a1d + b1d * b1d );
double h1d = im_col_ab2h( a1d, b1d );
double L2d = L2;
double a2d = (1 + G) * a2;
double b2d = b2;
double C2d = sqrt( a2d * a2d + b2d * b2d );
double h2d = im_col_ab2h( a2d, b2d );
/* L' bar, C' bar, h' bar
*/
double Ldb = (L1d + L2d) / 2;
double Cdb = (C1d + C2d) / 2;
double hdb = fabs( h1d - h2d ) < 180 ?
(h1d + h2d) / 2 :
fabs( h1d + h2d - 360 ) / 2;
/* dtheta, RC
*/
double hdbd = (hdb - 275) / 25;
double dtheta = 30 * exp( -(hdbd * hdbd) );
double Cdb7 = Cdb * Cdb * Cdb * Cdb * Cdb * Cdb * Cdb;
double RC = 2 * sqrt( Cdb7 / (Cdb7 + pow( 25, 7 )) );
/* RT, T.
*/
double RT = -sin( IM_RAD( 2 * dtheta ) ) * RC;
double T = 1 -
0.17 * cos( IM_RAD( hdb - 30 ) ) +
0.24 * cos( IM_RAD( 2 * hdb ) ) +
0.32 * cos( IM_RAD( 3 * hdb + 6 ) ) -
0.20 * cos( IM_RAD( 4 * hdb - 63 ) );
/* SL, SC, SH
*/
double Ldb50 = Ldb - 50;
double SL = 1 + (0.015 * Ldb50 * Ldb50) / sqrt( 20 + Ldb50 * Ldb50);
double SC = 1 + 0.045 * Cdb;
double SH = 1 + 0.015 * Cdb * T;
/* hue difference ... careful!
*/
double dhd = fabs( h1d - h2d ) < 180 ?
h1d - h2d :
360 - (h1d - h2d);
/* dLd, dCd dHd
*/
double dLd = L1d - L2d;
double dCd = C1d - C2d;
double dHd = 2 * sqrt( C1d * C2d ) * sin( IM_RAD( dhd / 2 ) );
/* Parametric factors for viewing parameters.
*/
const double kL = 1.0;
const double kC = 1.0;
const double kH = 1.0;
/* Normalised terms.
*/
double nL = dLd / (kL * SL);
double nC = dCd / (kC * SC);
double nH = dHd / (kH * SH);
/* dE00!!
*/
double dE00 = sqrt( nL * nL + nC * nC + nH * nH + RT * nC * nH );
/*
printf( "X1 = %g, Y1 = %g, Z1 = %g\n", X1, Y1, Z1 );
printf( "X2 = %g, Y2 = %g, Z2 = %g\n", X2, Y2, Z2 );
printf( "L1 = %g, a1 = %g, b1 = %g\n", L1, a1, b1 );
printf( "L2 = %g, a2 = %g, b2 = %g\n", L2, a2, b2 );
printf( "L1d = %g, a1d = %g, b1d = %g, C1d = %g, h1d = %g\n",
L1d, a1d, b1d, C1d, h1d );
printf( "L2d = %g, a2d = %g, b2d = %g, C2d = %g, h2d = %g\n",
L2d, a2d, b2d, C2d, h2d );
printf( "G = %g, T = %g, SL = %g, SC = %g, SH = %g, RT = %g\n",
G, T, SL, SC, SH, RT );
printf( "dE00 = %g\n", dE00 );
*/
return( dE00 );
}
