Mike,
Out of curiosity, at what image size (pixels) are you rendering, and are you using pfilt to filter down to the final image? I believe rendering many extra pixels with lower –ad and filtering down by /5, /10, etc. is the typical approach for the sake of rendering time when setting –aa 0. I’m not an expert in this, just recalling things I’ve seen in the distant past. I wonder if this approach would also reduce the size of those rendering artifacts.
···
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses