C# setHue (or alternatively, convert HSL to RGB an

Question

C# has a very convenient getHue method, but I can't find a setHue method. Is there one?

If not, I think the best way to define a color after changing the hue would be to convert the HSL value to RGB, and then set the RGB value. I know there are formulas on the internet for doing this, but how would I best go about performing this conversion from HSL to RGB using C#?

Thank You

Answer 1

System.Drawing.Color is a value type, which are almost always made immutable, especially in frameworks. That's why you can't setHue on it, you can only construct a new value type with fields you need.

So, if you have a function that will give you RGB values for your HSB values, you can do it like this

Color oldColor = ...;
int red, green, blue;
FromHSB(oldColor.GetHue(), oldColor.GetSaturation(), oldColor.GetBrightness(), out red, out green out blue);
Color newColor = Color.FromArgb(oldColor.A, red, green, blue);

where FromHSB looks like this

void FromHSB(float hue, float saturation, float brightness, out int red, out int green, out int blue)
{
    // ...
}

Answer 2

To set the Hue you create a new Color, maybe from a given one by using GetHue and GetSaturation. See below for the getBrightness function!

I'm using this:

Color SetHue(Color oldColor)
{
    var temp = new HSV();
    temp.h = oldColor.GetHue();
    temp.s = oldColor.GetSaturation();
    temp.v = getBrightness(oldColor);
    return ColorFromHSL(temp);
}

// A common triple float struct for both HSL & HSV
// Actually this should be immutable and have a nice constructor!!
public struct HSV { public float h; public float s; public float v;}

// the Color Converter
static public Color ColorFromHSL(HSV hsl)
{
    if (hsl.s == 0)
    { int L = (int)hsl.v; return Color.FromArgb(255, L, L, L); }

    double min, max, h;
    h = hsl.h / 360d;

    max = hsl.v < 0.5d ? hsl.v * (1 + hsl.s) : (hsl.v + hsl.s) - (hsl.v * hsl.s);
    min = (hsl.v * 2d) - max;

    Color c = Color.FromArgb(255, (int)(255 * RGBChannelFromHue(min, max,h + 1 / 3d)),
                                  (int)(255 * RGBChannelFromHue(min, max,h)), 
                                  (int)(255 * RGBChannelFromHue(min, max,h - 1 / 3d)));
    return c;
}

static double RGBChannelFromHue(double m1, double m2, double h)
{
    h = (h + 1d) % 1d;
    if (h < 0) h += 1;
    if (h * 6 < 1) return m1 + (m2 - m1) * 6 * h;
    else if (h * 2 < 1) return m2;
    else if (h * 3 < 2) return m1 + (m2 - m1) * 6 * (2d / 3d - h);
    else return m1;

}

Do not use the built-in GetBrightness method! It returns the same value (0.5f) for red, magenta, cyan, blue and yellow (!). This is better:

// color brightness as perceived:
float getBrightness(Color c)  
   {  return (c.R * 0.299f + c.G * 0.587f + c.B *0.114f) / 256f; }