/********************************************************************
 * 函數(shù)名稱：rgb2hsi
 * 功能：實現(xiàn)rgb到hsi的轉(zhuǎn)換
 * 參數(shù)：hsi  -  長度為3的雙精度數(shù)組
 *       rgb  -  長度為3的雙精度數(shù)組
 *******************************************************************/
void rgb2hsi(double *hsi, double *rgb)
{
	double& R = rgb[0];
	double& G = rgb[1];
	double& B = rgb[2];
	double& H = hsi[0];
	double& S = hsi[1];
	double& I = hsi[2];

	double min = R;
	if (G < min)
		min = G;
	if (B < min)
		min = B;

	I = (R+G+B)/3.0;
	S = 1 - min/I;
	if (S == 0.0)
	{
		H = 0.0;
    }
	else
	{
		H = ((R-G)+(R-B))/2.0;
		H = H/sqrt((R-G)*(R-G) + (R-B)*(G-B));
		H = acos(H);
		if (B > G)
		{
			H = 2*PI - H;
		}
		H = H/(2*PI);
	}
}