/// <summary>
/// Color quantization overview:
/// http://algolist.manual.ru/graphics/quant/qoverview.php
/// MSDN Article on changing palettes on GIFs
/// http://support.microsoft.com/default.aspx?scid=kb;en-us;Q319061
/// Median Cut Algorithm (simple, but slow)
/// http://rsb.info.nih.gov/ij/developer/source/ij/process/MedianCut.java.html (Java)
/// NeuQuant Algorithm (best quality, but slow)
/// http://www.acm.org/~dekker/NEUQUANT.HTML (Java)
/// Octree Quantization (fast)
/// http://www.microsoft.com/msj/archive/S3F1.aspx (Documentation)
/// http://www.microsoft.com/downloads/details.aspx?FamilyID=cb9a0bc8-c96b-4c3e-9652-df609352fa89&DisplayLang=en (Download)
///
/// </summary>
/// <param name="image"></param>
/// <param name="fTransparent"></param>
/// <returns></returns>
public static Bitmap GenerateGIFWithNewColorTable(
Bitmap image,
bool fTransparent, ColorReduction colorReductionAlgorithm)
{
// Make a new 8-BPP indexed bitmap that is the same size as the source image.
int nColors = 256;
int Width = image.Width;
int Height = image.Height;
// Always use PixelFormat8bppIndexed because that is the color
// table-based interface to the GIF codec.
Bitmap bitmap = new Bitmap(Width, Height, PixelFormat.Format8bppIndexed);
// Initialize a new color table with entries that are determined
IDictionary colorOccurences = new Hashtable();
IDictionary colorReducedOccurences = new Hashtable();
IDictionaryEnumerator cenum;
Color[] cpixels = new Color[Width * Height];
int ix = 0;
for (int y = 0; y < Height; y++)
{
for (int x = 0; x < Width; x++)
{
Color c = image.GetPixel(x, y);
cpixels[ix++] = c;
if (colorOccurences.Contains(c))
{
int v = (int)colorOccurences[c];
colorOccurences[c] = v++;
}
else colorOccurences[c] = 1;
}
}
IDictionary colorIndexMap = new Hashtable();
ColorPalette pal;
if (colorOccurences.Count <= 256)
{
nColors = colorOccurences.Count;
pal = GetColorPalette(nColors);
ix = 0;
cenum = colorOccurences.GetEnumerator();
while (cenum.MoveNext())
{
Color c = (Color)cenum.Key;
//ix = colorOccurences
colorIndexMap.Add(c, ix);
pal.Entries[ix++] = c;
}
}
else
{
// color reduction
DateTime sDate = DateTime.Now;
ColorQuantizer cq;
switch (colorReductionAlgorithm)
{
default: cq = new OctreeQuantizer(255, cpixels); break;
case ColorReduction.NEUQUANT: cq = new NeuQuant(30, cpixels); break;
}
cq.init();
cenum = colorOccurences.GetEnumerator();
while (cenum.MoveNext())
{
colorIndexMap.Add(cenum.Key, cq.lookup((Color)(cenum.Key)));
}
nColors = cq.getColorCount();
// GIF codec supports 256 colors maximum, monochrome minimum.
// Create a color palette big enough to hold the colors you want.
pal = GetColorPalette(nColors);
for (int x = 0; x < nColors; x++) pal.Entries[x] = cq.getColor(x);
//Common.logDebug("time for color reduction (" + colorOccurences.Count + " to 256) needed = " + ((TimeSpan)(DateTime.Now - sDate)).TotalMilliseconds + " ms");
}
// Set the palette into the new Bitmap object.
bitmap.Palette = pal;
// Lock a rectangular portion of the bitmap for writing.
BitmapData bitmapData;
Rectangle rect = new Rectangle(0, 0, Width, Height);
bitmapData = bitmap.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
// Write to the temporary buffer that is provided by LockBits.
// Copy the pixels from the source image in this loop.
// Because you want an index, convert RGB to the appropriate
// palette index here.
IntPtr pixels = bitmapData.Scan0;
//unsafe
//{
// // Get the pointer to the image bits. This is the unsafe operation.
// byte* pBits;
// if (bitmapData.Stride > 0) pBits = (byte*)pixels.ToPointer();
// else
// // If the Stide is negative, Scan0 points to the last
// // scanline in the buffer. To normalize the loop, obtain
// // a pointer to the front of the buffer that is located
// // (Height-1) scanlines previous.
// pBits = (byte*)pixels.ToPointer() + bitmapData.Stride * (Height - 1);
// uint stride = (uint)Math.Abs(bitmapData.Stride);
// for (uint row = 0; row < Height; ++row)
// {
// for (uint col = 0; col < Width; ++col)
// {
// // The destination pixel.
// // The pointer to the color index byte of the destination; this real pointer causes this
// // code to be considered unsafe.
// byte* p8bppPixel = pBits + row * stride + col;
// Color pixel = cpixels[Width * row + col];
// // determine index of that color
// object index = colorIndexMap[pixel];
// if (index != null)
// {
// *p8bppPixel = (byte)(int)index;
// }
// else
// {
// *p8bppPixel = 0;
// }
// } /* end loop for col */
// } /* end loop for row */
//} /* end unsafe */
// To commit the changes, unlock the portion of the bitmap.
bitmap.UnlockBits(bitmapData);
return bitmap;
}
public static void SaveGIFWithNewColorTable(
Bitmap image,
string filename,
bool fTransparent,
ColorReduction colorReductionAlgorithm
)
{
Bitmap bitmap = GenerateGIFWithNewColorTable(image, fTransparent, colorReductionAlgorithm);
bitmap.Save(filename, ImageFormat.Gif);
// Bitmap goes out of scope here and is also marked for
// garbage collection.
// Pal is referenced by bitmap and goes away.
bitmap.Dispose();
}