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!