well, I saw your message in the Bryce Forum and I had no idea. But now I am guessing maybe it is for saving an image that takes up less megabytes. Just a guess. It doesn't sound like a good reason for having a whole different type of rendering, but it could be possible. Or maybe it is there so that you can watch your image render and be able to see shapes in the image as it renders away. Ok, now I am getting weird. It is too late in the day. Sorry that I can't help ya Good Luck -Adam