How to change RGB color to HSV?

Question

How to change RGB color to HSV? In C# language. I search for very fast method without any external library.

Answer 1

See Wikipedia. It should be relatively straightforward to convert those formulas into code. Just be careful about the ranges of your inputs and outputs: are they floats between 0 and 1, integers between 0 and 255, or something else?

Answer 2

There's a C implementation here:

http://www.cs.rit.edu/~ncs/color/t_convert.html

Should be very straightforward to convert to C#, as almost no functions are called - just calculations.

found via Google

Answer 3

Have you considered simply using System.Drawing namespace? E.g.

System.Drawing.Color color = System.Drawing.Color.FromArgb(red, green, blue);
float hue = color.Gethue();
float saturation = color.GetSaturation();
float lightness = color.GetBrightness();

Note that it's not exactly what you've asked for (see differences between HSL and HSV and the Color class does not have a conversion back from HSL/HSV but the latter is reasonably easy to add.

Answer 4

This is the VB.net version which works fine for me ported from the C code in BlaM's post.

There's a C implementation here:

http://www.cs.rit.edu/~ncs/color/t_convert.html

Should be very straightforward to convert to C#, as almost no functions are called - just > calculations.

---

Public Sub HSVtoRGB(ByRef r As Double, ByRef g As Double, ByRef b As Double, ByVal h As Double, ByVal s As Double, ByVal v As Double)
    Dim i As Integer
    Dim f, p, q, t As Double

    If (s = 0) Then
        ' achromatic (grey)
        r = v
        g = v
        b = v
        Exit Sub
    End If

    h /= 60 'sector 0 to 5
    i = Math.Floor(h)
    f = h - i 'factorial part of h
    p = v * (1 - s)
    q = v * (1 - s * f)
    t = v * (1 - s * (1 - f))

    Select Case (i)
        Case 0
            r = v
            g = t
            b = p
            Exit Select
        Case 1
            r = q
            g = v
            b = p
            Exit Select
        Case 2
            r = p
            g = v
            b = t
            Exit Select
        Case 3
            r = p
            g = q
            b = v
            Exit Select
        Case 4
            r = t
            g = p
            b = v
            Exit Select
        Case Else   'case 5:
            r = v
            g = p
            b = q
            Exit Select
    End Select
End Sub

Answer 5

Note that Color.GetSaturation() and Color.GetBrightness() return HSL values, not HSV.
The following code demonstrates the difference.

Color original = Color.FromArgb(50, 120, 200);
// original = {Name=ff3278c8, ARGB=(255, 50, 120, 200)}

double hue;
double saturation;
double value;
ColorToHSV(original, out hue, out saturation, out value);
// hue        = 212.0
// saturation = 0.75
// value      = 0.78431372549019607

Color copy = ColorFromHSV(hue, saturation, value);
// copy = {Name=ff3278c8, ARGB=(255, 50, 120, 200)}

// Compare that to the HSL values that the .NET framework provides: 
original.GetHue();        // 212.0
original.GetSaturation(); // 0.6
original.GetBrightness(); // 0.490196079

The following C# code is what you want. It converts between RGB and HSV using the algorithms described on Wikipedia.

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);
}