如何制作依赖于System.Drawing命名空间的现有C#代码的Silverlight版本

// 原始代码
using System.Drawing;

public void DrawImage()
{
    Bitmap bitmap = new Bitmap(100, 100);
    Graphics graphics = Graphics.FromImage(bitmap);
    graphics.DrawImage(Image.FromFile("image.jpg"), new Point(0, 0));
    bitmap.Save("output.jpg");
}

// Silverlight版本
using System.Windows.Media;
using System.Windows.Media.Imaging;

public void DrawImage()
{
    WriteableBitmap bitmap = new WriteableBitmap(100, 100);
    WriteableBitmapExtensions.DrawImage(bitmap, new BitmapImage(new Uri("image.jpg", UriKind.Relative)), new System.Windows.Point(0, 0));
    bitmap.SaveJpeg(new FileStream("output.jpg", FileMode.Create), 100, 100, 0, 100);
}