Scaling WPF content before rendering to bitmap

This should be enough to get you started:

private void ExportCanvas(int width, int height){    string path = @"c:\temp\Test.tif";    FileStream fs = new FileStream(path, FileMode.Create);    RenderTargetBitmap renderBitmap = new RenderTargetBitmap(width,                                                             height, 1/300, 1/300, PixelFormats.Pbgra32);    DrawingVisual visual = new DrawingVisual();    using (DrawingContext context = visual.RenderOpen())    {        VisualBrush brush = new VisualBrush(MyCanvas);        context.DrawRectangle(brush,                              null,                              new Rect(new Point(), new Size(MyCanvas.Width, MyCanvas.Height)));    }    visual.Transform = new ScaleTransform(width / MyCanvas.ActualWidth, height / MyCanvas.ActualHeight);    renderBitmap.Render(visual);    BitmapEncoder encoder = new TiffBitmapEncoder();    encoder.Frames.Add(BitmapFrame.Create(renderBitmap));    encoder.Save(fs);    fs.Close();}

This is what ended up working for me:

Public Sub Capture(ByVal MyImage As Canvas)        ' Normally we would obtain a user's configured DPI setting to account for the possibilty of a high DPI setting.         ' However, this code is running server side so the client's DPI is not obtainable.        Const SCREEN_DPI As Double = 96.0   ' Screen DPI        Const TARGET_DPI As Double = 300.0  ' Print Quality DPI        ' Determine the constraining scale to maintain the aspect ratio and the bounds of the image size        Dim scale As Double = Math.Min(Width * SCREEN_DPI / MyImage.Width, Height * SCREEN_DPI / MyImage.Height)        ' Setup the bounds of the image        Dim bounds As Rect = New Rect(0, 0, MyImage.Width * scale, MyImage.Height * scale)        MyImage.Measure(New Size(MyImage.Width * scale, MyImage.Height * scale))        MyImage.Arrange(bounds)        ' Create the target bitmap        Dim rtb As RenderTargetBitmap = New RenderTargetBitmap(CDbl(MyImage.Width * scale / SCREEN_DPI * TARGET_DPI), CDbl(MyImage.Height * scale / SCREEN_DPI * TARGET_DPI), TARGET_DPI, TARGET_DPI, PixelFormats.Pbgra32)        ' Render the image to the target bitmap        Dim dv As DrawingVisual = New DrawingVisual()        Using ctx As DrawingContext = dv.RenderOpen()            Dim vb As New VisualBrush(MyImage)            ctx.DrawRectangle(vb, Nothing, New Rect(New System.Windows.Point(), bounds.Size))        End Using        ' Transform the visual to scale the image to our desired size.        'dv.Transform = New ScaleTransform(scale, scale)        ' Render the visual to the bitmap.        rtb.Render(dv)        ' Encode the image in the format selected. If no valid format was selected, default to png.        Dim encoder As System.Windows.Media.Imaging.BitmapEncoder        Select Case Encoding.ToLower            Case "jpg"                encoder = New System.Windows.Media.Imaging.JpegBitmapEncoder()            Case "png"                encoder = New System.Windows.Media.Imaging.PngBitmapEncoder()            Case "gif"                encoder = New System.Windows.Media.Imaging.GifBitmapEncoder()            Case "bmp"                encoder = New System.Windows.Media.Imaging.BmpBitmapEncoder()            Case "tif"                encoder = New System.Windows.Media.Imaging.TiffBitmapEncoder()            Case "wmp"                encoder = New System.Windows.Media.Imaging.WmpBitmapEncoder()            Case Else                encoder = New System.Windows.Media.Imaging.PngBitmapEncoder()        End Select        encoder.Frames.Add(System.Windows.Media.Imaging.BitmapFrame.Create(rtb))        ' Create the memory stream to save the encoded image.        retImageStream = New System.IO.MemoryStream()        encoder.Save(retImageStream)        retImageStream.Flush()        retImageStream.Seek(0, System.IO.SeekOrigin.Begin)        MyImage = Nothing    End Sub