ColorExtensions.cs

using System;
using System.Drawing;

namespace FMUtils.Screenshot
{
    public static class ColorExtensions
    {
        public static Color HSL2RGB(double h, double sl, double l)
        {
            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;
                }
            }
            Color rgb = Color.FromArgb(Convert.ToByte(r * 255.0f), Convert.ToByte(g * 255.0f), Convert.ToByte(b * 255.0f));
            return rgb;
        }

        public static void ColorToHSV(Color color, out double hue, out double saturation, out double value)
        {
            int max = Math.Max(color.R, Math.Max(color.G, color.B));
            int min = Math.Min(color.R, Math.Min(color.G, color.B));

            hue = color.GetHue();
            saturation = (max == 0) ? 0 : 1d - (1d * min / max);
            value = max / 255d;
        }

        public static Color ColorFromHSV(double hue, double saturation, double value)
        {
            int hi = Convert.ToInt32(Math.Floor(hue / 60)) % 6;
            double f = hue / 60 - Math.Floor(hue / 60);

            value = value * 255;
            int v = Convert.ToInt32(value);
            int p = Convert.ToInt32(value * (1 - saturation));
            int q = Convert.ToInt32(value * (1 - f * saturation));
            int t = Convert.ToInt32(value * (1 - (1 - f) * saturation));

            if (hi == 0)
                return Color.FromArgb(255, v, t, p);
            else if (hi == 1)
                return Color.FromArgb(255, q, v, p);
            else if (hi == 2)
                return Color.FromArgb(255, p, v, t);
            else if (hi == 3)
                return Color.FromArgb(255, p, q, v);
            else if (hi == 4)
                return Color.FromArgb(255, t, p, v);
            else
                return Color.FromArgb(255, v, p, q);
        }
    }
}