using (var imageStreamSource = File.OpenRead(@"r:\4.png"))
    using (Stream fs = File.Create(@"r:\test.png"))
    {
        var decoder = BitmapDecoder.Create(imageStreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
        var bitmapFrame = decoder.Frames[0];

        var size = new Size(bitmapFrame.PixelWidth, bitmapFrame.PixelHeight);
        var img = new Image() { Source = bitmapFrame };
        img.Effect = new System.Windows.Media.Effects.DropShadowEffect();
        img.Arrange(new Rect(0,0,bitmapFrame.PixelWidth,bitmapFrame.PixelHeight));

        var rtb = new RenderTargetBitmap(bitmapFrame.PixelWidth, bitmapFrame.PixelHeight, 96, 96, PixelFormats.Pbgra32);
        rtb.Render(img);
        var png = new PngBitmapEncoder();
        png.Frames.Add(BitmapFrame.Create(rtb));
        png.Save(fs);
    }

    Image myImage = new Image();
    FormattedText text = new FormattedText("ABC",
            new CultureInfo("en-us"),
            FlowDirection.LeftToRight,
            new Typeface(this.FontFamily, FontStyles.Normal, FontWeights.Normal, new FontStretch()),
            this.FontSize,
            this.Foreground);

    DrawingVisual drawingVisual = new DrawingVisual();
    DrawingContext drawingContext = drawingVisual.RenderOpen();
    drawingContext.DrawText(text, new Point(2, 2));
    drawingContext.Close();

    RenderTargetBitmap bmp = new RenderTargetBitmap(180, 180, 120, 96, PixelFormats.Pbgra32);
    bmp.Render(drawingVisual);
    myImage.Source = bmp;

    Ellipse cir = new Ellipse();
    cir.Height = 50;
    cir.Width = 50;
    cir.Stroke = Brushes.Black;
    cir.StrokeThickness = 1.0;
    cir.Arrange(new Rect(new Size(50, 50)));    //這句不能漏了

    RenderTargetBitmap rtb = new RenderTargetBitmap(200, 200, 96, 96, PixelFormats.Pbgra32);
    rtb.Render(cir);

    PngBitmapEncoder png = new PngBitmapEncoder();
    png.Frames.Add(BitmapFrame.Create(rtb));
    using (Stream fs = File.Create(@"r:\test.png"))
    {
        png.Save(fs);
    }