How do I adjust the brightness of a color?

Question

I would like to darken an existing color for use in a gradient brush. Could somebody tell me how to do this please?

C#, .net 2.0, GDI+

Answer 1

As a simple approach, you can just factor the RGB values:

    Color c1 = Color.Red;
    Color c2 = Color.FromArgb(c1.A,
        (int)(c1.R * 0.8), (int)(c1.G * 0.8), (int)(c1.B * 0.8));

(which should darken it; or, for example, * 1.25 to brighten it)

Answer 2

You could also try using

ControlPaint.Light(baseColor, percOfLightLight)

ControlPaint.Light

or

ControlPaint.Dark(baseColor, percOfDarkDark)

ControlPaint.Dark

Answer 3

Convert from RGB to HSV (or HSL), then adjust the V (or L) down and then convert back.

While System.Drawing.Color provides methods to get hue (H), saturation (S) and brightness it does not provide much in the way of other conversions, notable nothing to create a new instance from HSV (or HSV values), but the conversion is pretty simple to implement. The wikipedia articles give decent converage, starting here: "HSL and HSV".

Answer 4

Here's some C# code for the conversions Richard mentioned:

RGB to HSL / HSL to RGB in C#

Answer 5

While the aforementioned methods do darken the color but they adjust the hue way to much so the result doesn't look very good. The best answer is to use Rich Newman's HSLColor class and adjust the luminosity.

public Color Darken(Color color, double darkenAmount) {
    HSLColor hslColor = new HSLColor(color);
    hslColor.Luminosity *= darkenAmount; // 0 to 1
    return hslColor;
}

Answer 6

You must keep track that the value does not extend below 0 or above 255

Best approach is to use Math.Max/Math.MIn

dim newValue as integer = ...
'correct value if it is below 0 or above 255
newValue = Math.Max(Math.Min(newValue,255),0)