Thanks for input guys :-) i have tried the remedies youve suggested and it helps the luminosity map was in uncompressed tiff but i made a separate map just to make sure there werent any stray pixels involved, and i dropped the texture filtering too which helped. im starting to think that the displacement is somehow driving the problem. ive tried lowering the value and it also helps,but i DO need some displacement as just using the bump map doesnt come out too well

 A cleaved head no longer plots.

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