/// <summary>
/// Convert from RGB to HSL color space.
/// </summary>
/// <param name="rgb">Source color in <b>RGB</b> color space.</param>
/// <param name="hsl">Destination color in <b>HSL</b> color space.</param>
/// <remarks>
/// <para>
/// See
/// <a href="http://en.wikipedia.org/wiki/HSI_color_space#Conversion_from_RGB_to_HSL_or_HSV">HSL and HSV Wiki</a>
/// for information about the algorithm to convert from RGB to HSL.
/// </para>
/// </remarks>
public static void FromRGB([NotNull] Rgb rgb, [NotNull] Hsl hsl)
{
float r = rgb.Red / 255.0f;
float g = rgb.Green / 255.0f;
float b = rgb.Blue / 255.0f;
float min = Math.Min(Math.Min(r, g), b);
float max = Math.Max(Math.Max(r, g), b);
float delta = max - min;
// get luminance value
hsl.Luminance = (max + min) / 2;
if (Math.Abs(delta) < float.Epsilon)
{
// gray color
hsl.Hue = 0;
hsl.Saturation = 0.0f;
}
else
{
// get saturation value
hsl.Saturation = hsl.Luminance <= 0.5
? delta / (max + min)
: delta / (2 - max - min);
// get hue value
float hue = Math.Abs(r - max) < float.Epsilon
? (g - b) / 6 / delta
: Math.Abs(g - max) < float.Epsilon
? 1.0f / 3 + (b - r) / 6 / delta
: 2.0f / 3 + (r - g) / 6 / delta;
// correct hue if needed
if (hue < 0)
{
hue += 1;
}
if (hue > 1)
{
hue -= 1;
}
hsl.Hue = (int)(hue * 360);
}
}
/// <summary>
/// Convert from HSL to RGB color space.
/// </summary>
/// <param name="hsl">Source color in <b>HSL</b> color space.</param>
/// <param name="rgb">Destination color in <b>RGB</b> color space.</param>
public static void ToRGB([NotNull] Hsl hsl, [NotNull] Rgb rgb)
{
if (Math.Abs(hsl.Saturation) < float.Epsilon)
{
// gray values
rgb.Red = rgb.Green = rgb.Blue = (byte)(hsl.Luminance * 255);
}
else
{
float hue = (float)hsl.Hue / 360;
float v2 = hsl.Luminance < 0.5
? hsl.Luminance * (1 + hsl.Saturation)
: hsl.Luminance + hsl.Saturation - hsl.Luminance * hsl.Saturation;
float v1 = 2 * hsl.Luminance - v2;
rgb.Red = (byte)(255 * Hue_2_RGB(v1, v2, hue + 1.0f / 3));
rgb.Green = (byte)(255 * Hue_2_RGB(v1, v2, hue));
rgb.Blue = (byte)(255 * Hue_2_RGB(v1, v2, hue - 1.0f / 3));
}
rgb.Alpha = 255;
}
