/// <summary>
/// quantizes the specified image using a floyd-steinberg error diffusion dithering
/// </summary>
private unsafe void QuantizeFloydSteinberg(ColorBgra *pixels, int width, int height)
{
if (_octree == null)
{
return;
}
int index = 0;
ColorBgra col;
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++, index++)
{
col = _octree.Table[_octree.GetOctreeIndex(pixels[index])];
int er = (int)pixels[index].R - (int)col.R,
eg = (int)pixels[index].G - (int)col.G,
eb = (int)pixels[index].B - (int)col.B;
#region error matrix
for (int i = 0; i < 2; i++)
{
int iy = i + y;
if (iy >= 0 && iy < height)
{
for (int j = -1; j < 2; j++)
{
int jx = j + x;
if (jx >= 0 && jx < width)
{
//load error dispersion from matrix
int w = floydsteinbergmatrix[i][j + 1];
if (w != 0)
{
int k = jx + iy * width;
pixels[k].Red += (er * w) / floydsteinbergsum;
pixels[k].Green += (eg * w) / floydsteinbergsum;
pixels[k].Blue += (eb * w) / floydsteinbergsum;
}
}
}
}
#endregion
}
pixels[index] = col;
}
}
}
/// <summary>
/// writes the image to the specified stream
/// </summary>
public override void Write(Stream str)
{
if (str == null)
{
throw new ArgumentNullException("str");
}
//write header
BITMAPINFOHEADER header = new BITMAPINFOHEADER(
_bitmap.Size,
_bitsperpixel,
this.SizeInBytes,
(1 << _bitsperpixel) & 0xFF);
header.Write(str);
using (SimpleWriter wrt = new SimpleWriter(str))
{
#region write palette
foreach (ColorBgra value in _octree.Table)
{
wrt.Write(value.B);
wrt.Write(value.G);
wrt.Write(value.R);
wrt.Write((byte)0); //reserved
}
#endregion
#region write indexed data
//write bitmap
BitmapData bd = _bitmap.LockBits(
new Rectangle(Point.Empty, _bitmap.Size),
ImageLockMode.ReadWrite,
PixelFormat.Format32bppArgb);
ColorBgra *scan0 = (ColorBgra *)bd.Scan0;
//write indexed data
int indexmask = (1 << _bitsperpixel) - 1,
indexdata = 0;
scan0 += bd.Width * bd.Height;
for (int y = 0; y < bd.Height; y++)
{
scan0 -= bd.Width;
int indexpos = 8 - _bitsperpixel;
indexdata = 0;
for (int x = 0; x < bd.Width; x++)
{
indexdata |=
(_octree.GetOctreeIndex(scan0[x]) & indexmask) << indexpos;
if (indexpos % 8 == 0)
{
indexpos += (16 - _bitsperpixel);
}
else
{
indexpos -= _bitsperpixel;
}
if (indexpos >= 32)
{
wrt.Write(indexdata);
indexdata = 0;
indexpos -= 32;
}
}
if (indexpos != (8 - _bitsperpixel))
{
wrt.Write(indexdata);
}
}
ANDMap.WriteToStream(bd, wrt);
#endregion
_bitmap.UnlockBits(bd);
}
}