[code]
public static Bitmap GrayscaleImage(Image img)
{
	int width = img.Width;
	int heigth = img.Height;
	
	Bitmap source = (Bitmap)img;
		
	for (int i=0; i<width; i++)
		for (int j=0; j<heigth; j++)
		{
			Color pixelColor = source.GetPixel(i, j);
			byte R = Convert.ToByte(255 - pixelColor.R);
			byte G = Convert.ToByte(255 - pixelColor.G);
			byte B = Convert.ToByte(255 - pixelColor.B);
			byte value = Convert.ToByte( (R+G+B)/3 );
			source.SetPixel(i, j, Color.FromArgb(value, value, value));
		}
			
	return source;
}
[/code]