C#

<br />
	public class BitmapSubsystem<br />
	{<br />
		public static readonly BitmapSubsystem Instance = new BitmapSubsystem();<br />
<br />
		protected ColorPalette GetMonoColorPalette()<br />
		{<br />
			// Make a new Bitmap object to get its Palette.<br />
			Bitmap bitmap = new Bitmap( 1, 1, PixelFormat.Format1bppIndexed );<br />
<br />
			ColorPalette palette = bitmap.Palette;   // Grab the palette<br />
<br />
			palette.Entries[0] = Color.FromArgb( (int)0xFF, (int)0, (int)0,(int)0 ); // Black<br />
			palette.Entries[1] = Color.FromArgb( (int)0, (int)255, (int)255,(int)255 ); // Transparent<br />
<br />
			bitmap.Dispose();           // cleanup the source Bitmap<br />
<br />
			return palette;             // Send the palette back<br />
		}<br />
<br />
		public void ConvertTo2bppBitmap( Bitmap sourceBitmap, Stream output )<br />
		{<br />
			// Make a new 8-BPP indexed bitmap that is the same size as the source image.<br />
			int   Width = sourceBitmap.Width;<br />
			int   Height = sourceBitmap.Height;<br />
<br />
			// Always use PixelFormat8bppIndexed because that is the color<br />
			// table-based interface to the GIF codec.<br />
			Bitmap  bitmap = new Bitmap(Width, Height, PixelFormat.Format8bppIndexed);<br />
<br />
			try<br />
			{<br />
				// Create a color palette big enough to hold the colors you want.<br />
				ColorPalette pal = GetMonoColorPalette();<br />
<br />
				// Set the palette into the new Bitmap object.<br />
				bitmap.Palette = pal;<br />
<br />
				// Lock a rectangular portion of the bitmap for writing.<br />
				BitmapData  bitmapData;<br />
				Rectangle   rect = new Rectangle(0, 0, Width, Height);<br />
<br />
				bitmapData = bitmap.LockBits( rect, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);<br />
<br />
				// Write to the temporary buffer that is provided by LockBits.<br />
				// Copy the pixels from the source image in this loop.<br />
				// Because you want an index, convert RGB to the appropriate<br />
				// palette index here.<br />
				IntPtr pixels = bitmapData.Scan0;<br />
<br />
				unsafe<br />
				{<br />
					// Get the pointer to the image bits.<br />
					// This is the unsafe operation.<br />
					byte *  pBits;<br />
					if (bitmapData.Stride > 0)<br />
						pBits = (byte *)pixels.ToPointer();<br />
					else<br />
						// If the Stride is negative, Scan0 points to the last<br />
						// scanline in the buffer. To normalize the loop, obtain<br />
						// a pointer to the front of the buffer that is located<br />
						// (Height-1) scanlines previous.<br />
						pBits = (byte *)pixels.ToPointer() + bitmapData.Stride*(Height-1);<br />
					<br />
					uint stride = (uint)Math.Abs(bitmapData.Stride);<br />
<br />
					for ( uint row = 0; row < Height; ++row )<br />
					{<br />
						for ( uint col = 0; col < Width; ++col )<br />
						{<br />
							// Map palette indexes for a gray scale.<br />
							// If you use some other technique to color convert,<br />
							// put your favorite color reduction algorithm here.<br />
<br />
							// The destination pixel.<br />
							// The pointer to the color index byte of the<br />
							// destination; this real pointer causes this<br />
							// code to be considered unsafe.<br />
							byte *    p2bppPixel = pBits + row*stride + col;<br />
<br />
							Color srcPixel = sourceBitmap.GetPixel((int)col, (int)row);<br />
<br />
							// This expression is best as integer math for performance,<br />
							// however, because GetPixel listed earlier is the slowest<br />
							// part of this loop, the expression is left as<br />
							// floating point for clarity.<br />
							double luminance = (srcPixel.R *0.299) + (srcPixel.G *0.587) + (srcPixel.B *0.114);<br />
<br />
							// If the luminance is > 0 then use the non-transparent palette entry<br />
							if( luminance > 0 )<br />
								*p2bppPixel = (byte)(1);<br />
							else<br />
								*p2bppPixel = (byte)(0);<br />
<br />
						} /* end loop for col */<br />
					} /* end loop for row */<br />
				} /* end unsafe */<br />
<br />
				// To commit the changes, unlock the portion of the bitmap.<br />
				bitmap.UnlockBits(bitmapData);<br />
<br />
				bitmap.Save(output, ImageFormat.Gif);<br />
			}<br />
			catch<br />
			{<br />
			}<br />
<br />
			// Bitmap goes out of scope here and is also marked for<br />
			// garbage collection.<br />
			// Pal is referenced by bitmap and goes away.<br />
			bitmap.Dispose();<br />
		}	<br />