Oh forgot to mention that I see most bump maps made by the naive are almost entirely mid gray or damn close. This means that the full set of variation in the bump map must be encoded into only a handful of values, for example from 126 to 131. Thus, the effective quantization of such a bump map is less than 3 bits, instead of the full 8 bits it should be.

A properly made bump map has black and white in it, not just shades of gray. Then you adjust the bump amount to scale those values into the tiny range you really need for pores and such.

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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)