Silverlight把WriteableBitmap转为Byte流并保存到本地

算法核心：对WriteableBitmap的所有像素点做循环遍历，然后存入Byte[]数组中，再转换为MemoryStream输出，下面是代码：

private void ButtonSave_Click(object sender, RoutedEventArgs e)
        {
            WriteableBitmap bitmap = new WriteableBitmap(MyStackPanel, null);

            if (bitmap != null)
            {
                SaveFileDialog saveDlg = new SaveFileDialog();
                saveDlg.Filter = "JPEG Files (*.jpeg)|*.jpeg";
                saveDlg.DefaultExt = ".jpeg";

                if ((bool)saveDlg.ShowDialog())
                {
                    using (Stream fs = saveDlg.OpenFile())
                    {
                        SaveToFile(bitmap, fs);
                        MessageBox.Show("File save Complete");
                    }
                }
            }
        }

        private static void SaveToFile(WriteableBitmap bitmap, Stream fs)
        {
            int width = bitmap.PixelWidth;
            int height = bitmap.PixelHeight;
            int bands = 3;
            byte[][,] raster = new byte[bands][,];

            for (int i = 0; i < bands; i++)
            {
                raster[i] = new byte[width, height];
            }

            for (int row = 0; row < height; row++)
            {
                for (int column = 0; column < width; column++)
                {
                    int pixel = bitmap.Pixels[width * row + column];
                    raster[0][column, row] = (byte)(pixel >> 16);
                    raster[1][column, row] = (byte)(pixel >> 8);
                    raster[2][column, row] = (byte)pixel;
                }

            }

            FluxJpeg.Core.ColorModel model = new FluxJpeg.Core.ColorModel { colorspace = FluxJpeg.Core.ColorSpace.RGB };
            FluxJpeg.Core.Image img = new FluxJpeg.Core.Image(model, raster);


            //Encode the Image as a JPEG
            MemoryStream stream = new MemoryStream();
            FluxJpeg.Core.Encoder.JpegEncoder encoder = new FluxJpeg.Core.Encoder.JpegEncoder(img, 100, stream);
            encoder.Encode();

            //Back to the start
            stream.Seek(0, SeekOrigin.Begin);

            //Get teh Bytes and write them to the stream
            byte[] binaryData = new Byte[stream.Length];
            long bytesRead = stream.Read(binaryData, 0, (int)stream.Length);
            fs.Write(binaryData, 0, binaryData.Length);
        }

我对其中的这一段尤其不满意，自觉是性能的关键，有没有更高效的算法快速从WriteableBitmap直接得到像素的Byte[]数组？

for (int row = 0; row < height; row++)
            {
                for (int column = 0; column < width; column++)
                {
                    int pixel = bitmap.Pixels[width * row + column];
                    raster[0][column, row] = (byte)(pixel >> 16);
                    raster[1][column, row] = (byte)(pixel >> 8);
                    raster[2][column, row] = (byte)pixel;
                }

            }