C# RGB to HSL / HSL
This seems to be something difficult to find, but extremely useful for creating colour schemes that look nice. I needed to create my own colour class for persistent storage reasons. The technique below works just as easily by replacing the ColorRGB references with a simple ::System.Drawing.Color. My Color class provides operators to convert to and from System.Drawing.Color
public struct ColorRGB
{
public byte R;
public byte G;
public byte B;
public ColorRGB(Color value)
{
this.R = value.R;
this.G = value.G;
this.B = value.B;
}
public static implicit operator Color(ColorRGB rgb)
{
Color c = Color.FromArgb(rgb.R,rgb.G,rgb.B);
return c;
}
public static explicit operator ColorRGB(Color c)
{
return new ColorRGB(c);
}
}
This function will take an HSL value in the ranges of 0-1 and return a color object. I use this function all the time.
// Given H,S,L in range of 0-1
// Returns a Color (RGB struct) in range of 0-255
public static ColorRGB 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;
}
}
ColorRGB rgb;
rgb.R = Convert.ToByte(r * 255.0f);
rgb.G = Convert.ToByte(g * 255.0f);
rgb.B = Convert.ToByte(b * 255.0f);
return rgb;
}
To be honest – I haven’t yet needed to convert an RGB into an HSL, but if I did – this is what I would do
// Given a Color (RGB Struct) in range of 0-255
// Return H,S,L in range of 0-1
public static void RGB2HSL (ColorRGB rgb, out double h, out double s, out double l)
{
double r = rgb.R/255.0;
double g = rgb.G/255.0;
double b = rgb.B/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;
}