BitmapExtensionsAdjustContrast Method

Adjusts the contrast of the specified bitmap.

Definition

Namespace: KGySoft.Drawing
Assembly: KGySoft.Drawing (in KGySoft.Drawing.dll) Version: 9.0.0

C#

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

VB

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

C++

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

F#

[<ExtensionAttribute>]
static member AdjustContrast : 
        bitmap : Bitmap * 
        contrast : 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.
contrast Single: A float value between -1 and 1, inclusive bounds. Positive values increase the contrast, while negative values decrease the 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

In Visual Basic and C#, you can call this method as an instance method on any object of type Bitmap. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

Remarks

Note

This method adjusts the degree of parallelization automatically, blocks the caller, and does not support cancellation or reporting progress. Use the BitmapDataExtensions.BeginAdjustContrast or BitmapDataExtensions.AdjustContrastAsync (in .NET Framework 4.0 and above) methods for asynchronous call and to adjust parallelization, set up cancellation and for reporting progress.

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.

Examples

The following example demonstrates how to use this method:

C#

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 the contrast. 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 contrast values and ColorChannels, too.
bmp.AdjustContrast(-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

Exceptions

ArgumentNullException	bitmap is .
ArgumentOutOfRangeException	contrast is not between -1 and 1 -or- channels is out of the defined flags.