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【CSharp】保存GIF透明

作者:zgke / 发布于2014/7/29/ 470

转换图形为GIF格式，获取GIF的的颜色表。发现只有颜色索引表16的alpha是0 就是透明色。根据图形的ALPHA为0的情况下来设置颜色索引表。使用方式如果要保存图形为透明把具体位置的ALPHA的值设置为0


	Bitmap _Bitmap24 = (Bitmap)Image.FromFile(@"C:/bfx/24.bmp");
	pictureBox1.Image = ToImageGif(_Bitmap24);
	Bitmap _BitmapGDI = new Bitmap(200, 200);
	Graphics g = Graphics.FromImage(_BitmapGDI);
	g.DrawString("ASDF", new Font("宋体", 20), Brushes.Yellow, new Point(0, 0));
	pictureBox2.Image = ToImageGif(_BitmapGDI);
	pictureBox2.Image.Save(@"c:/1.GIF", ImageFormat.Gif);

	

	具体方法

	private static Bitmap ToImageGif(Bitmap MyBitMap)
	 {
	 int _Width = MyBitMap.Width;
	 int _Height = MyBitMap.Height;
	
	 System.IO.MemoryStream _MemoryStream = new MemoryStream();
	 MyBitMap.Save(_MemoryStream, ImageFormat.Gif);
	 Bitmap _MyBitMap256 = (Bitmap)Image.FromStream(_MemoryStream); //保存成GIF 256色
	 _MemoryStream.Dispose();
	 //获取颜色索引
	 System.Drawing.Imaging.ColorPalette _ColorPalette = _MyBitMap256.Palette;
	 Hashtable _ColorHash = new Hashtable();
	 for (int i = 0; i != _ColorPalette.Entries.Length; i++)
	 {
	
	 string _Key=_ColorPalette.Entries[i].R.ToString("X02")+_ColorPalette.Entries[i].G.ToString("X02")+_ColorPalette.Entries[i].B.ToString("X02");
	
	 if(_ColorHash[_Key]==null)_ColorHash.Add(_Key, i);
	 }
	
	 ////建立新的图形
	 Bitmap _Newbitmap = new Bitmap(_Width, _Height, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
	 _Newbitmap.Palette = _ColorPalette; //设置索引
	 Rectangle _Rect = new Rectangle(0, 0, _Width, _Height);
	 //获取IMAGE数据
	 System.Drawing.Imaging.BitmapData _BitmapData = _Newbitmap.LockBits(_Rect, System.Drawing.Imaging.ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
	 byte[] _Bits = new byte[_Width * _Height];
	 Int32 _BitsInt = 0;
	 if (_BitmapData.Stride > 0)
	 {
	 _BitsInt = _BitmapData.Scan0.ToInt32();
	 }
	 else
	 {
	 _BitsInt = _BitmapData.Scan0.ToInt32() + _BitmapData.Stride * (_Height - 1);
	 }
	 int _Stride = Math.Abs(_BitmapData.Stride);
	 for (int i = 0; i != _Height; i++)
	 {
	 for (int y = 0; y != _Width; y++)
	 {
	 int _8BppPixel = i * _Stride + y;
	 Color _TempColor=_MyBitMap256.GetPixel(y, i);
	 int _Alpha = MyBitMap.GetPixel(y, i).A;
	 if (_Alpha == 0)
	 {
	 _Bits[_8BppPixel] = (byte)16;
	 }
	 else
	 {
	 string _Key = _TempColor.R.ToString("X02") + _TempColor.G.ToString("X02") + _TempColor.B.ToString("X02");
	 object _ValueIndex = _ColorHash[_Key];
	 if (_ValueIndex == null) MessageBox.Show("Error");
	 _Bits[_8BppPixel] = (byte)((int)_ValueIndex);
	 }
	
	 }
	 }
	 CopyArrayTo(_BitsInt, _Bits, _Height * _Stride);
	 _Newbitmap.UnlockBits(_BitmapData);
	 return _Newbitmap;
	 }
	
	 [DllImport("KERNEL32.DLL", EntryPoint = "RtlMoveMemory", SetLastError = true, CharSet = CharSet.Auto, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
	 public static extern void CopyArrayTo([In(), MarshalAs(UnmanagedType.I4)] Int32 hpvDest, [In(), Out()]byte[] hpvSource, int cbCopy);

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　保存GIF透明　　 GIF透明　　 GIF　

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