public static void SaveDynamicCanvas(DynamicCanvas canvas, int dpi, string filename)
{
Size size = new Size(canvas.Width, canvas.Height);
canvas.Measure(size);
canvas.Arrange(new Rect(size));
var rtb = new RenderTargetBitmap(
(int)canvas.Width, //width
(int)canvas.Height, //height
dpi, //dpi x
dpi, //dpi y
PixelFormats.Pbgra32 // pixelformat
);
rtb.Render(canvas);
SaveRTBAsPNG(rtb, filename);
}