BitmapExtensionsAdjustGamma Method

public static void AdjustGamma(
	this Bitmap bitmap,
	float gamma,
	IDitherer? ditherer = null,
	ColorChannels channels = ColorChannels.Rgb
)

<ExtensionAttribute>
Public Shared Sub AdjustGamma ( 
	bitmap As Bitmap,
	gamma As Single,
	Optional ditherer As IDitherer = Nothing,
	Optional channels As ColorChannels = ColorChannels.Rgb
)

public:
[ExtensionAttribute]
static void AdjustGamma(
	Bitmap^ bitmap, 
	float gamma, 
	IDitherer^ ditherer = nullptr, 
	ColorChannels channels = ColorChannels::Rgb
)

[<ExtensionAttribute>]
static member AdjustGamma : 
        bitmap : Bitmap * 
        gamma : float32 * 
        ?ditherer : IDitherer * 
        ?channels : ColorChannels 
(* Defaults:
        let _ditherer = defaultArg ditherer null
        let _channels = defaultArg channels ColorChannels.Rgb
*)
-> unit 

Parameters

bitmap  Bitmap

The Bitmap to be transformed.

gamma  Single

A float value between 0 and 10, inclusive bounds. Values less than 1 decrease gamma correction, while values above 1 increase it.

ditherer  IDitherer  (Optional)

An optional IDitherer instance to dither the result of the transformation if the transformed colors are not compatible with the PixelFormat of the specified bitmap. This parameter is optional.
Default value: .

channels  ColorChannels  (Optional)

The ColorChannels, on which the adjustment has to be performed. This parameter is optional.
Default value: Rgb.

Usage Note

If bitmap has an indexed PixelFormat and ditherer is , then its palette entries will be transformed instead of the actual pixels. To transform the colors of an indexed Bitmap without changing the palette specify a non- ditherer. Transforming the palette is both faster and provides a better result.

The ditherer is ignored for PixelFormats with more than 16 bits-per-pixel and for the Format16bppGrayScale format.

Example 1: Simple usage

using Bitmap bmp = Icons.Shield.ExtractBitmap(new Size(256, 256));
bmp.SaveAsPng(@"c:\temp\before.png");
bmp.AdjustGamma(0.5f);
bmp.SaveAsPng(@"c:\temp\after.png");

The example above produces the following results:

before.png
after.png

Example 2: Adjusting the gamma of an indexed bitmap with dithering

By default, adjusting the gamma of an indexed bitmap transforms the palette entries only, which is both faster and provides a better result. To force using the original palette, you can specify a non- ditherer:

using Bitmap original = Icons.Shield.ExtractBitmap(new Size(256, 256));

// starting with an indexed image using an optimized 8 BPP palette
using Bitmap bmp = original.ConvertPixelFormat(PixelFormat.Format8bppIndexed,
    OptimizedPaletteQuantizer.MedianCut());

bmp.SaveAsGif(@"c:\temp\before.gif");

// Decreasing gamma. By specifying a ditherer the original palette is preserved
// (which is not so optimal for the transformed image anymore). The ditherer tries
// to approximate the desired result with the original palette as much as possible.
// Try it also without a ditherer to transform only the palette entries.
// Try different values and ColorChannels, too.
bmp.AdjustGamma(0.5f, ErrorDiffusionDitherer.FloydSteinberg, ColorChannels.Rgb);

// As ditherer was not null now the result is generated using the original palette
bmp.SaveAsGif(@"c:\temp\after.gif");

The example above produces the following results:

before.gif
after.gif

Example 3: Using linear color space

using Bitmap bmp = Icons.Shield.ExtractBitmap(new Size(256, 256));
bmp.SaveAsPng(@"c:\temp\before.png");
using (IReadWriteBitmapData bitmapData = bmp.GetReadWriteBitmapData(WorkingColorSpace.Linear))
    bitmapData.AdjustGamma(0.5f);
bmp.SaveAsPng(@"c:\temp\after.png");

The example above produces the following results:

before.png
after.png

Reference