PredefinedColorsQuantizerSystemDefault8BppPalette Method

public static PredefinedColorsQuantizer SystemDefault8BppPalette(
	Color backColor = default,
	byte alphaThreshold = 128
)

Public Shared Function SystemDefault8BppPalette ( 
	Optional backColor As Color = Nothing,
	Optional alphaThreshold As Byte = 128
) As PredefinedColorsQuantizer

public:
static PredefinedColorsQuantizer^ SystemDefault8BppPalette(
	Color backColor = Color(), 
	unsigned char alphaThreshold = 128
)

static member SystemDefault8BppPalette : 
        ?backColor : Color * 
        ?alphaThreshold : byte 
(* Defaults:
        let _backColor = defaultArg backColor new Color()
        let _alphaThreshold = defaultArg alphaThreshold 128
*)
-> PredefinedColorsQuantizer 

Parameters

backColor  Color  (Optional)

Colors with alpha (transparency), which are considered opaque will be blended with this color before quantization. The Color.A property of the background color is ignored. This parameter is optional.
Default value: Empty, which has the same RGB values as Black.

alphaThreshold  Byte  (Optional)

If the system default 8-bit palette contains a transparent color on the current operating system, then specifies a threshold value for the Color.A property, under which a quantized color is considered transparent. If 0, then the quantized colors will never be transparent. This parameter is optional.
Default value: 128.

Return Value

The returned PredefinedColorsQuantizer instance can return up to 256 colors. Actually this amount is somewhat smaller because of some redundant entries in the palette.

This quantizer fits well for the Format8bppIndexed pixel format.

The palette of this quantizer contains transparent entries.

public static IReadWriteBitmapData ToDefault8Bpp(IReadWriteBitmapData source, Color backColor = default,
    byte alphaThreshold = 128, IDitherer ditherer = null)
{
    IQuantizer quantizer = PredefinedColorsQuantizer.SystemDefault8BppPalette(backColor, alphaThreshold);

    // a.) this solution returns a new bitmap data and does not change the original one:
    return source.Clone(KnownPixelFormat.Format8bppIndexed, quantizer, ditherer);

    // b.) when converting to Format8bppIndexed format without dithering, this produces the same result:
    if (ditherer == null)
        return source.Clone(KnownPixelFormat.Format8bppIndexed, backColor, alphaThreshold);

    // c.) alternatively, you can perform the quantization directly on the source bitmap data:
    if (ditherer == null)
        source.Quantize(quantizer);
    else
        source.Dither(quantizer, ditherer);
    return source;
}

The example above may produce the following results:

Reference