Dispatcher.BeginInvoke instead of Thread

        void Canvas_MouseUp(object sender, MouseEventArgs e)
        {
            leftMouseDown = false;

            var curLayer = GetItemsPanel((canvasDataBinding.ItemContainerGenerator.ContainerFromIndex(0)));
            exportToImage(curLayer.ActualWidth, curLayer.ActualHeight, curLayer);
            //Thread RASTERIZE_THREAD = new Thread(new ThreadStart(() => { exportToImage(curLayer.ActualWidth, curLayer.ActualHeight, curLayer); }));
            //RASTERIZE_THREAD.Start();
        }

        ...

        void exportToImage(double width, double height, Visual visual)
        {
            var filename = string.Format(@"{0}.png", Guid.NewGuid());
            var tempFile = Path.Combine(tempDir, filename);
            Rect rect = new Rect(0, 0, width, height);

            this.Dispatcher.BeginInvoke(new Action(() =>
            {
                RenderTargetBitmap rtb = new RenderTargetBitmap((int)rect.Right,
                (int)rect.Bottom, 96d, 96d, System.Windows.Media.PixelFormats.Default);
                rtb.Render(visual);
                //endcode as PNG
                BitmapEncoder pngEncoder = new PngBitmapEncoder();
                pngEncoder.Frames.Add(BitmapFrame.Create(rtb));

                //save to memory stream
                System.IO.MemoryStream ms = new System.IO.MemoryStream();

                pngEncoder.Save(ms);
                ms.Close();
                System.IO.File.WriteAllBytes(tempFile, ms.ToArray());
                updateCanvas(tempFile);
                this.Title = "images in canvas after rasterizing: " + canvasImages[0].Count;
            }), DispatcherPriority.Background);
        }