public BitmapImage Crop(Rectangle pixelRect)
{
var scaleX = Math.Truncate (PixelWidth / Width);
var scaleY = Math.Truncate (PixelHeight / Height);
return new BitmapImage (ToolkitEngine.ImageBackendHandler.CropBitmap (Backend, (int)pixelRect.X, (int)pixelRect.Y, (int)pixelRect.Width, (int)pixelRect.Height), new Size (pixelRect.Width / scaleX, pixelRect.Height / scaleY), ToolkitEngine);
}