How to: Encode a Visual to an Image File
This example demonstrates how to encode a Visual object into an image file using a RenderTargetBitmapand 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
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
// 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);
}
A PngBitmapEncoder was used in this example but any of the derived BitmapEncoder objects could have been used to create the image file.