The IDL precalc gets bigger based on image size. As a result, your memory consumption can be rather huge if you are doing something in the multi-megapixel range. Some people were running out of memory very often.

To help with that, you can use that to change the IDL precalc as if you were doing a smaller image. For example, if have a 2K by 2K image but you set the precalc scale to .5, the precalc will act like it's a 1K by 1K image, and save you 3/4 of the RAM it normally uses.

The downside is detail/resolution may be lost (not that important for IDL) and artifacts will be bigger.

Everything in CG is some kind of nasty trade-off.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)