RGBHSVConversion.cs

using System;

namespace Algorithms.Other
{
    /// <summary>
    ///     The RGB color model is an additive color model in which red, green, and
    ///     blue light are added together in various ways to reproduce a broad array of
    ///     colors. The name of the model comes from the initials of the three additive
    ///     primary colors, red, green, and blue. Meanwhile, the HSV representation
    ///     models how colors appear under light. In it, colors are represented using
    ///     three components: hue, saturation and (brightness-)value. This class
    ///     provides methods for converting colors from one representation to the other.
    ///     (description adapted from https://en.wikipedia.org/wiki/RGB_color_model and
    ///     https://en.wikipedia.org/wiki/HSL_and_HSV).
    /// </summary>
    public static class RgbHsvConversion
    {
        /// <summary>
        ///     Conversion from the HSV-representation to the RGB-representation.
        /// </summary>
        /// <param name="hue">Hue of the color.</param>
        /// <param name="saturation">Saturation of the color.</param>
        /// <param name="value">Brightness-value of the color.</param>
        /// <returns>The tuple of RGB-components.</returns>
        public static (byte red, byte green, byte blue) HsvToRgb(
            double hue,
            double saturation,
            double value)
        {
            if (hue < 0 || hue > 360)
            {
                throw new ArgumentOutOfRangeException(nameof(hue), $"{nameof(hue)} should be between 0 and 360");
            }

            if (saturation < 0 || saturation > 1)
            {
                throw new ArgumentOutOfRangeException(
                    nameof(saturation),
                    $"{nameof(saturation)} should be between 0 and 1");
            }

            if (value < 0 || value > 1)
            {
                throw new ArgumentOutOfRangeException(nameof(value), $"{nameof(value)} should be between 0 and 1");
            }

            var chroma = value * saturation;
            var hueSection = hue / 60;
            var secondLargestComponent = chroma * (1 - Math.Abs(hueSection % 2 - 1));
            var matchValue = value - chroma;

            return GetRgbBySection(hueSection, chroma, matchValue, secondLargestComponent);
        }

        /// <summary>
        ///     Conversion from the RGB-representation to the HSV-representation.
        /// </summary>
        /// <param name="red">Red-component of the color.</param>
        /// <param name="green">Green-component of the color.</param>
        /// <param name="blue">Blue-component of the color.</param>
        /// <returns>The tuple of HSV-components.</returns>
        public static (double hue, double saturation, double value) RgbToHsv(
            byte red,
            byte green,
            byte blue)
        {
            var dRed = (double)red / 255;
            var dGreen = (double)green / 255;
            var dBlue = (double)blue / 255;
            var value = Math.Max(Math.Max(dRed, dGreen), dBlue);
            var chroma = value - Math.Min(Math.Min(dRed, dGreen), dBlue);
            var saturation = value.Equals(0) ? 0 : chroma / value;
            double hue;

            if (chroma.Equals(0))
            {
                hue = 0;
            }
            else if (value.Equals(dRed))
            {
                hue = 60 * (0 + (dGreen - dBlue) / chroma);
            }
            else if (value.Equals(dGreen))
            {
                hue = 60 * (2 + (dBlue - dRed) / chroma);
            }
            else
            {
                hue = 60 * (4 + (dRed - dGreen) / chroma);
            }

            hue = (hue + 360) % 360;

            return (hue, saturation, value);
        }

        private static (byte red, byte green, byte blue) GetRgbBySection(
            double hueSection,
            double chroma,
            double matchValue,
            double secondLargestComponent)
        {
            byte red;
            byte green;
            byte blue;

            if (hueSection >= 0 && hueSection <= 1)
            {
                red = ConvertToByte(chroma + matchValue);
                green = ConvertToByte(secondLargestComponent + matchValue);
                blue = ConvertToByte(matchValue);
            }
            else if (hueSection > 1 && hueSection <= 2)
            {
                red = ConvertToByte(secondLargestComponent + matchValue);
                green = ConvertToByte(chroma + matchValue);
                blue = ConvertToByte(matchValue);
            }
            else if (hueSection > 2 && hueSection <= 3)
            {
                red = ConvertToByte(matchValue);
                green = ConvertToByte(chroma + matchValue);
                blue = ConvertToByte(secondLargestComponent + matchValue);
            }
            else if (hueSection > 3 && hueSection <= 4)
            {
                red = ConvertToByte(matchValue);
                green = ConvertToByte(secondLargestComponent + matchValue);
                blue = ConvertToByte(chroma + matchValue);
            }
            else if (hueSection > 4 && hueSection <= 5)
            {
                red = ConvertToByte(secondLargestComponent + matchValue);
                green = ConvertToByte(matchValue);
                blue = ConvertToByte(chroma + matchValue);
            }
            else
            {
                red = ConvertToByte(chroma + matchValue);
                green = ConvertToByte(matchValue);
                blue = ConvertToByte(secondLargestComponent + matchValue);
            }

            return (red, green, blue);
        }

        private static byte ConvertToByte(double input) => (byte)Math.Round(255 * input);
    }
}