PredefinedColorsQuantizerGrayscale4 Method

public static PredefinedColorsQuantizer Grayscale4(
	Color backColor = default,
	bool directMapping = false
)

Public Shared Function Grayscale4 ( 
	Optional backColor As Color = Nothing,
	Optional directMapping As Boolean = false
) As PredefinedColorsQuantizer

public:
static PredefinedColorsQuantizer^ Grayscale4(
	Color backColor = Color(), 
	bool directMapping = false
)

static member Grayscale4 : 
        ?backColor : Color * 
        ?directMapping : bool 
(* Defaults:
        let _backColor = defaultArg backColor new Color()
        let _directMapping = defaultArg directMapping false
*)
-> PredefinedColorsQuantizer 

Parameters

backColor  Color  (Optional)

Colors with alpha (transparency) 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.

directMapping  Boolean  (Optional)

to map any color directly to an index instead of searching for a nearest color, which is very fast but may end up in a result of a bit higher contrast than the original image; to perform a lookup to determine nearest colors, which may be slower but more accurate. This parameter is optional.
Default value: .

Return Value

If directMapping is , then the result of the quantization may have a higher contrast than without direct color mapping, though this can be compensated if the returned quantizer is combined with an ErrorDiffusionDitherer. Other ditherers preserve the effect of the directMapping parameter.

The returned PredefinedColorsQuantizer instance can return up to 4 possible shades of gray.

This quantizer fits well for the Format4bppIndexed pixel format, though only 4 palette entries are used instead of the possible maximum of 16.

public static IReadWriteBitmapData ToGrayscale4(IReadWriteBitmapData source, Color backColor = default, bool directMapping = false, IDitherer ditherer = null)
{
    IQuantizer quantizer = PredefinedColorsQuantizer.Grayscale4(backColor, directMapping);

    // a.) this solution returns a new bitmap data and does not change the original one:
    return source.Clone(KnownPixelFormat.Format4bppIndexed, quantizer, ditherer);

    // b.) 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