private static void BuildHistogram(Histogram histogram, ImageBuffer imageBuffer, int alphaThreshold, int alphaFader)
{
ColorMoment[, , ,] moments = histogram.Moments;
foreach (Color32[] pixelLine in imageBuffer.PixelLines)
{
foreach (Color32 pixel in pixelLine)
{
byte pixelAlpha = pixel.A;
if (pixelAlpha > alphaThreshold)
{
if (pixelAlpha < 255)
{
int alpha = pixel.A + (pixel.A % alphaFader);
pixelAlpha = (byte)(alpha > 255 ? 255 : alpha);
}
byte pixelRed = pixel.R;
byte pixelGreen = pixel.G;
byte pixelBlue = pixel.B;
pixelAlpha = (byte)((pixelAlpha >> 3) + 1);
pixelRed = (byte)((pixelRed >> 3) + 1);
pixelGreen = (byte)((pixelGreen >> 3) + 1);
pixelBlue = (byte)((pixelBlue >> 3) + 1);
moments[pixelAlpha, pixelRed, pixelGreen, pixelBlue].Add(pixel);
}
}
}
// Set a default pixel for images with less than 256 colors.
moments[0, 0, 0, 0].Add(new Color32(0, 0, 0, 0));
}
/// <summary>
/// Quantize an image and return the resulting output bitmap
/// </summary>
/// <param name="source">
/// The 32 bit per pixel image to quantize.
/// </param>
/// <param name="alphaThreshold">
/// All colors with an alpha value less than this will be considered fully transparent.
/// </param>
/// <param name="alphaFader">
/// Alpha values will be normalized to the nearest multiple of this value.
/// </param>
/// <param name="histogram">
/// The <see cref="Histogram"/> representing the distribution of color data.
/// </param>
/// <param name="maxColors">
/// The maximum number of colors apply to the image.
/// </param>
/// <returns>
/// A quantized version of the image.
/// </returns>
public Bitmap Quantize(Image source, int alphaThreshold, int alphaFader, Histogram histogram, int maxColors)
{
try
{
ImageBuffer buffer;
// The image has to be a 32 bit per pixel Argb image.
if (Image.GetPixelFormatSize(source.PixelFormat) != 32)
{
Bitmap clone = new Bitmap(source.Width, source.Height, PixelFormat.Format32bppPArgb);
clone.SetResolution(source.HorizontalResolution, source.VerticalResolution);
using (Graphics graphics = Graphics.FromImage(clone))
{
graphics.PageUnit = GraphicsUnit.Pixel;
graphics.Clear(Color.Transparent);
graphics.DrawImageUnscaled(source, new Rectangle(0, 0, clone.Width, clone.Height));
}
source.Dispose();
buffer = new ImageBuffer(clone);
}
else
{
buffer = new ImageBuffer((Bitmap)source);
}
if (histogram == null)
{
histogram = new Histogram();
}
else
{
histogram.Clear();
}
BuildHistogram(histogram, buffer, alphaThreshold, alphaFader);
CalculateMoments(histogram.Moments);
Box[] cubes = SplitData(ref maxColors, histogram.Moments);
Color32[] lookups = BuildLookups(cubes, histogram.Moments);
return this.GetQuantizedImage(buffer, maxColors, lookups, alphaThreshold);
}
catch (Exception ex)
{
throw new QuantizationException(ex.Message, ex);
}
}