Save wpf view as image, preferably .png

You can return it as RenderTargetBitmap:

public static RenderTargetBitmap GetImage(OverallView view)
{
    Size size = new Size(view.ActualWidth, view.ActualHeight);
    if (size.IsEmpty)
        return null;

    RenderTargetBitmap result = new RenderTargetBitmap((int)size.Width, (int)size.Height, 96, 96, PixelFormats.Pbgra32);

    DrawingVisual drawingvisual = new DrawingVisual();
    using (DrawingContext context = drawingvisual.RenderOpen())
    {
        context.DrawRectangle(new VisualBrush(view), null, new Rect(new Point(), size));
        context.Close();
    }

    result.Render(drawingvisual);
    return result;
}

After that you can use the PngBitmapEncoder to save it as PNG and save it to stream, e.g.:

public static void SaveAsPng(RenderTargetBitmap src, Stream outputStream)
{
    PngBitmapEncoder encoder = new PngBitmapEncoder();
    encoder.Frames.Add(BitmapFrame.Create(src));

    encoder.Save(outputStream);   
}

FIX: bitmap => result