色差及范围界定
前段时间，关于主色提取方面，用到了色差的概念。色差是应用在Lab颜色空间上的，个人感觉效果还可以，不知道为何关于这方面的应用不是很多，是不是有什么大的弊端，还请大家多多指教！
色差相关定义可以参阅：http://www.cgan.net/book/books/print/packcolor/link/5-4-3.html
code：
/******************************************************************************
*
* CIEDE2000 Color Difference Calculator
*
* Copyright (c) 2007 yoneh (http://d.hatena.ne.jp/yoneh/)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*
******************************************************************************
*
* References:
* [1] Gaurav Sharma, Wencheng Wu, and Edul N. Dalal, ``The CIEDE2000 Color-
* Difference Formula: Implementation Notes, Supplementary Test Data,
* and Mathematical Observations'', Color Research and Application, Vol. 30,
* No. 1, Feb 2005.
*
******************************************************************************/
#include <cmath>
#include <iostream>
using namespace std;
double CIEDE2000(const double L1,const double a1,const double b1,
const double L2,const double a2,const double b2);
int main(void)
{
double L1,a1,b1;
double L2,a2,b2;
cout << "<<< CIEDE2000 Color Difference Calculator >>>" << endl << endl;
cout << "L1 = ";
cin >> L1;
cout << "a1 = ";
cin >> a1;
cout << "b1 = ";
cin >> b1;
cout << endl;
cout << "L2 = ";
cin >> L2;
cout << "a2 = ";
cin >> a2;
cout << "b2 = ";
cin >> b2;
cout << endl;
cout << "E00 = " << CIEDE2000(L1,a1,b1,L2,a2,b2) << endl;
return 0;
}
/**
* Can x be assumed to be 0
* @param x a value
* @return true if x can be assumed to be 0
*/
inline bool tolerance_zero(const double x)
{
return fabs(x)<1e-9;
}
/**
* cosine
* @param degree angle [degree]
* @return cosine value
*/
inline double cosd(const double degree)
{
return cos(degree*M_PI/180.0);
}
/**
* sine
* @param degree angle [degree]
* @return sine value
*/
inline double sind(const double degree)
{
return sin(degree*M_PI/180.0);
}
/**
* arctangent (four quadrant)
* @param y y-coordinate
* @param x x-coordinate
* @return angle [degree]
*/
inline double fqatan(const double y,const double x)
{
double t=atan2(y,x)/M_PI*180.0;
if(t<0.0)
t+=360.0;
return t;
}
/**
* Calculate f7(x)=(x^7 / (x^7+25^7))^0.5
* @param x a value
* @return f7(x)
*/
inline double f7(const double x)
{
// if x is small, using the following approx.
if(x<1.0)
return pow(x/25.0,3.5);
return 1.0/sqrt(1.0+pow(25.0/x,7.0));
}
/**
* Calculate `CIEDE2000 Color Difference'
* @param L1 L* parameter of a color
* @param a1 a* parameter of a color
* @param b1 b* parameter of a color
* @param L2 L* parameter of a color
* @param a2 a* parameter of a color
* @param b2 b* parameter of a color
* @return `CIEDE2000 Color Difference' between (L1,a1,b1) and (L2,a2,b2)
*/
double CIEDE2000(const double L1,const double a1,const double b1,
const double L2,const double a2,const double b2)
{
const double epsilon=1e-9;
// Calculate C1', C2', h1', and h2'
double C1ab,C2ab;
double Cab,G;
double a1_,a2_;
double C1_,C2_;
double h1_,h2_;
C1ab=sqrt(a1*a1+b1*b1);
C2ab=sqrt(a2*a2+b2*b2);
Cab=(C1ab+C2ab)/2.0;
G=0.5*(1.0-f7(Cab));
a1_=(1.0+G)*a1;
a2_=(1.0+G)*a2;
C1_=sqrt(a1_*a1_+b1*b1);
C2_=sqrt(a2_*a2_+b2*b2);
if(tolerance_zero(a1_) && tolerance_zero(b1))
h1_=0.0;
else
h1_=fqatan(b1,a1_);
if(tolerance_zero(a2_) && tolerance_zero(b2))
h2_=0.0;
else
h2_=fqatan(b2,a2_);
// Calculate dL', dC', and dH'
double dL_,dC_,dH_,dh_;
double C12;
dL_=L2-L1;
dC_=C2_-C1_;
C12=C1_*C2_;
if(tolerance_zero(C12))
{
dh_=0.0;
}
else
{
double tmp=h2_-h1_;
if(fabs(tmp)<=180.0+epsilon)
dh_=tmp;
else if(tmp>180.0)
dh_=tmp-360.0;
else if(tmp<-180.0)
dh_=tmp+360.0;
}
dH_=2.0*sqrt(C12)*sind(dh_/2.0);
// Calculate L', C', h', T, and dTh
double L_,C_,h_,T,dTh;
L_=(L1+L2)/2.0;
C_=(C1_+C2_)/2.0;
if(tolerance_zero(C12))
{
h_=h1_+h2_;
}
else
{
double tmp1=fabs(h1_-h2_);
double tmp2=h1_+h2_;
if(tmp1<=180.0+epsilon)
h_=tmp2/2.0;
else if(tmp2<360.0)
h_=(tmp2+360.0)/2.0;
else if(tmp2>=360.0)
h_=(tmp2-360.0)/2.0;
}
T=1.0-0.17*cosd(h_-30.0)+0.24*cosd(2.0*h_)
+0.32*cosd(3.0*h_+6.0)-0.2*cosd(4.0*h_-63.0);
dTh=30.0*exp(-pow((h_-275.0)/25.0,2.0));
// Calculate RC, SL, SC, SH, and RT
double RC,SL,SC,SH,RT;
double L_2=(L_-50.0)*(L_-50.0);
RC=2.0*f7(C_);
SL=1.0+0.015*L_2/sqrt(20.0+L_2);
SC=1.0+0.045*C_;
SH=1.0+0.015*C_*T;
RT=-sind(2.0*dTh)*RC;
// Calculate dE00
const double kL=1.0; // These are proportionally coefficients
const double kC=1.0; // and vary according to the condition.
const double kH=1.0; // These mostly are 1.
double LP=dL_/(kL*SL);
double CP=dC_/(kC*SC);
double HP=dH_/(kH*SH);
return sqrt(LP*LP+CP*CP+HP*HP+RT*CP*HP);
}