#include <iostream.h>
#include <math.h>
#include <stdlib.h>

void rgb2hsi(double *hsi, double *rgb);

int main(int argc, char** argv) {

   if (argc != 4) {
      cout << "Usage: " << argv[0] << " R G B" << endl;
      exit(1);
   }

   double R = atof(argv[1]);
   double G = atof(argv[2]);
   double B = atof(argv[3]);

   if (R > 1.0) {
      R = R/256.0;
   }
   if (G > 1.0) {
      G = G/256.0;
   }
   if (B > 1.0) {
      B = B/256.0;
   }
   double rgb[3];
   rgb[0] = R;
   rgb[1] = G;
   rgb[2] = B;

   double hsi[3] = {0};

   rgb2hsi(hsi, rgb);

   cout << "H = " << hsi[0] << endl;
   cout << "S = " << hsi[1] << endl;
   cout << "I = " << hsi[2] << endl;

   return 0;
}


//////////////////////////////////////////////////////////////////////////


//////////////////////////////
//
// rgb2hsi -- convert from RGB color space to HSI color space.
//

#ifndef PI
   #define PI M_PI
#endif

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);
   }
}