HSL.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace AtmoLight
{
  public static class HSL
  {
    // RGB2HSL and HSL2RGB
    //
    // http://www.geekymonkey.com/Programming/CSharp/RGB2HSL_HSL2RGB.htm

    // Given H,S,L in range of 0-1
    // Returns r,g,b in range of 0-255
    public static void HSL2RGB(double h, double sl, double l, out int red, out int green, out int blue)
    {
      double v;
      double r, g, b;

      r = l;   // default to gray
      g = l;
      b = l;
      v = (l <= 0.5) ? (l * (1.0 + sl)) : (l + sl - l * sl);
      if (v > 0)
      {
        double m;
        double sv;
        int sextant;
        double fract, vsf, mid1, mid2;

        m = l + l - v;
        sv = (v - m) / v;
        h *= 6.0;
        sextant = (int)h;
        fract = h - sextant;
        vsf = v * sv * fract;
        mid1 = m + vsf;
        mid2 = v - vsf;
        switch (sextant)
        {
          case 0:
            r = v;
            g = mid1;
            b = m;
            break;
          case 1:
            r = mid2;
            g = v;
            b = m;
            break;
          case 2:
            r = m;
            g = v;
            b = mid1;
            break;
          case 3:
            r = m;
            g = mid2;
            b = v;
            break;
          case 4:
            r = mid1;
            g = m;
            b = v;
            break;
          case 5:
            r = v;
            g = m;
            b = mid2;
            break;
        }
      }
      red = Convert.ToByte(r * 255.0f);
      green = Convert.ToByte(g * 255.0f);
      blue = Convert.ToByte(b * 255.0f);
    }


    // Given r,g,b in range of 0-255
    // Return H,S,L in range of 0-1
    public static void RGB2HSL(int red, int green, int blue, out double h, out double s, out double l)
    {
      double r = red / 255.0;
      double g = green / 255.0;
      double b = blue / 255.0;
      double v;
      double m;
      double vm;
      double r2, g2, b2;

      h = 0; // default to black
      s = 0;
      l = 0;
      v = Math.Max(r, g);
      v = Math.Max(v, b);
      m = Math.Min(r, g);
      m = Math.Min(m, b);
      l = (m + v) / 2.0;
      if (l <= 0.0)
      {
        return;
      }
      vm = v - m;
      s = vm;
      if (s > 0.0)
      {
        s /= (l <= 0.5) ? (v + m) : (2.0 - v - m);
      }
      else
      {
        return;
      }
      r2 = (v - r) / vm;
      g2 = (v - g) / vm;
      b2 = (v - b) / vm;
      if (r == v)
      {
        h = (g == m ? 5.0 + b2 : 1.0 - g2);
      }
      else if (g == v)
      {
        h = (b == m ? 1.0 + r2 : 3.0 - b2);
      }
      else
      {
        h = (r == m ? 3.0 + g2 : 5.0 - r2);
      }
      h /= 6.0;
    }
  }
}