Okay, I made a "green paint splotch" with an alpha map for transparency, and applied it to a square (from props>primitives). This worked fine (transparency wise), and looks just fine in the preview, but when rendered it has serious blocking. The blocking is just that,  blocks, which divide the texture into square chunks of two different luminosities, it looks like...normal, and darker-than-normal. The only fiddling that seems to affect this situation directly is to change the pixel samples number in the render settings, but this is no cure as the results are unacceptable. The texture has enough resolution (it's not a close-up shot), and so this is not pixelation per se (at least, I don't think so). Any answers? Thanks!

Have you tried reversing the normals? You can click that option in the material room, it sounds like the problem you're having but without a picture I can't be sure.

-Sarah

ps
min shade rate also directly affects it, but no cure.
When I say "directly affects" it (both in pixel samples and min shade rate), I mean it changes how big the chunks are and how the chunks are "patterned". But, no cure. The cure would be, the lighter luminosity would be uniform.

Sarah, thanks! That's the cure! Normals, forward!
Project, forward!
ur beautiful!

Glad I could help :-)

-Sarah