How to: Encode a Visual to an Image File

This example demonstrates how to encode a Visual object into an image file using a RenderTargetBitmap and a PngBitmapEncoder.

Example

The DrawingVisual is created using a BitmapImage and FormattedText which is rendered to a RenderTargetBitmap. The rendered bitmap is then used to create a BitmapFrame which is added to the PngBitmapEncoder to create a new Portable Network Graphics (PNG) file.

// Base Image
BitmapImage bi = new BitmapImage();
bi.BeginInit();
bi.UriSource = new Uri("sampleImages/waterlilies.jpg",UriKind.Relative);
bi.DecodePixelWidth = 200;
bi.EndInit();

// Text to render on the image.
FormattedText text = new FormattedText("Waterlilies",
        new CultureInfo("en-us"),
        FlowDirection.LeftToRight,
        new Typeface(this.FontFamily, FontStyles.Normal, FontWeights.Normal, new FontStretch()),
        this.FontSize,
        Brushes.White);

// The Visual to use as the source of the RenderTargetBitmap.
DrawingVisual drawingVisual = new DrawingVisual();
DrawingContext drawingContext = drawingVisual.RenderOpen();
drawingContext.DrawImage(bi,new Rect(0,0,bi.Width,bi.Height)); 
drawingContext.DrawText(text, new Point(bi.Height/2, 0));
drawingContext.Close();

// The BitmapSource that is rendered with a Visual.
RenderTargetBitmap rtb = new RenderTargetBitmap(bi.PixelWidth, bi.PixelHeight, 96, 96, PixelFormats.Pbgra32);
rtb.Render(drawingVisual);

// Encoding the RenderBitmapTarget as a PNG file.
PngBitmapEncoder png = new PngBitmapEncoder();
png.Frames.Add(BitmapFrame.Create(rtb));
using (Stream stm = File.Create("new.png"))
{
   png.Save(stm);
}
' Base Image
Dim bi As New BitmapImage()
bi.BeginInit()
bi.UriSource = New Uri("sampleImages/waterlilies.jpg", UriKind.Relative)
bi.DecodePixelWidth = 200
bi.EndInit()

' Text to render on the image.
Dim [text] As New FormattedText("Waterlilies", New CultureInfo("en-us"), System.Windows.FlowDirection.LeftToRight, New Typeface(Me.FontFamily, FontStyles.Normal, FontWeights.Normal, New FontStretch()), Me.FontSize, Brushes.White)

' The Visual to use as the source of the RenderTargetBitmap.
Dim drawingVisual As New DrawingVisual()
Dim drawingContext As DrawingContext = drawingVisual.RenderOpen()
drawingContext.DrawImage(bi, New Rect(0, 0, bi.Width, bi.Height))
drawingContext.DrawText([text], New System.Windows.Point(bi.Height / 2, 0))
drawingContext.Close()

' The BitmapSource that is rendered with a Visual.
Dim rtb As New RenderTargetBitmap(bi.PixelWidth, bi.PixelHeight, 96, 96, PixelFormats.Pbgra32)
rtb.Render(drawingVisual)

' Encoding the RenderBitmapTarget as a PNG file.
Dim png As New PngBitmapEncoder()
png.Frames.Add(BitmapFrame.Create(rtb))
Dim stm As Stream = File.Create("new.png")
Try
    png.Save(stm)
Finally
    stm.Dispose()
End Try

A PngBitmapEncoder was used in this example but any of the derived BitmapEncoder objects could have been used to create the image file.

See also