Simple RGB/HSV conversion in C++

hsvrgb-cpp

// Copyright (c) 2014, Jan Winkler <winkler@cs.uni-bremen.de>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
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//       this software without specific prior written permission.
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/* Author: Jan Winkler */


#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;


/*! \brief Convert RGB to HSV color space
  
  Converts a given set of RGB values `r', `g', `b' into HSV
  coordinates. The input RGB values are in the range [0, 1], and the
  output HSV values are in the ranges h = [0, 360], and s, v = [0,
  1], respectively.
  
  \param fR Red component, used as input, range: [0, 1]
  \param fG Green component, used as input, range: [0, 1]
  \param fB Blue component, used as input, range: [0, 1]
  \param fH Hue component, used as output, range: [0, 360]
  \param fS Hue component, used as output, range: [0, 1]
  \param fV Hue component, used as output, range: [0, 1]
  
*/
void RGBtoHSV(float& fR, float& fG, float fB, float& fH, float& fS, float& fV) {
  float fCMax = max(max(fR, fG), fB);
  float fCMin = min(min(fR, fG), fB);
  float fDelta = fCMax - fCMin;
  
  if(fDelta > 0) {
    if(fCMax == fR) {
      fH = 60 * (fmod(((fG - fB) / fDelta), 6));
    } else if(fCMax == fG) {
      fH = 60 * (((fB - fR) / fDelta) + 2);
    } else if(fCMax == fB) {
      fH = 60 * (((fR - fG) / fDelta) + 4);
    }
    
    if(fCMax > 0) {
      fS = fDelta / fCMax;
    } else {
      fS = 0;
    }
    
    fV = fCMax;
  } else {
    fH = 0;
    fS = 0;
    fV = fCMax;
  }
  
  if(fH < 0) {
    fH = 360 + fH;
  }
}


/*! \brief Convert HSV to RGB color space
  
  Converts a given set of HSV values `h', `s', `v' into RGB
  coordinates. The output RGB values are in the range [0, 1], and
  the input HSV values are in the ranges h = [0, 360], and s, v =
  [0, 1], respectively.
  
  \param fR Red component, used as output, range: [0, 1]
  \param fG Green component, used as output, range: [0, 1]
  \param fB Blue component, used as output, range: [0, 1]
  \param fH Hue component, used as input, range: [0, 360]
  \param fS Hue component, used as input, range: [0, 1]
  \param fV Hue component, used as input, range: [0, 1]
  
*/
void HSVtoRGB(float& fR, float& fG, float& fB, float& fH, float& fS, float& fV) {
  float fC = fV * fS; // Chroma
  float fHPrime = fmod(fH / 60.0, 6);
  float fX = fC * (1 - fabs(fmod(fHPrime, 2) - 1));
  float fM = fV - fC;
  
  if(0 <= fHPrime && fHPrime < 1) {
    fR = fC;
    fG = fX;
    fB = 0;
  } else if(1 <= fHPrime && fHPrime < 2) {
    fR = fX;
    fG = fC;
    fB = 0;
  } else if(2 <= fHPrime && fHPrime < 3) {
    fR = 0;
    fG = fC;
    fB = fX;
  } else if(3 <= fHPrime && fHPrime < 4) {
    fR = 0;
    fG = fX;
    fB = fC;
  } else if(4 <= fHPrime && fHPrime < 5) {
    fR = fX;
    fG = 0;
    fB = fC;
  } else if(5 <= fHPrime && fHPrime < 6) {
    fR = fC;
    fG = 0;
    fB = fX;
  } else {
    fR = 0;
    fG = 0;
    fB = 0;
  }
  
  fR += fM;
  fG += fM;
  fB += fM;
}


int main(int argc, char** argv) {
  float fR = 0, fG = 0, fB = 0, fH = 0, fS = 0, fV = 0;
  
  fH = 146.0;
  fS = 0.19;
  fV = 0.66;
  
  HSVtoRGB(fR, fG, fB, fH, fS, fV);

  /*fR = 136.0;
    fG = 168.0;
    fB = 150.0;
    
    RGBtoHSV(fR, fG, fB, fH, fS, fV);*/
  
  cout << "[RGB] "
       << "Float:   (" << fR << ", " << fG << ", " << fB << ")" << endl
       << "      Integer: (" << (255 * fR) << ", " << (255 * fG) << ", " << (255 * fB) << ")" << endl;
  cout << "[HSV] (" << fH << ", " << fS << ", " << fV << ")" << endl;
  
  return EXIT_SUCCESS;
}