I’d seen a strange error (or maybe I’m doing something wrong).
I have a rotate layer rotating a group. Synfig render it right in screen but, when I render frames to PNG, for make the animation, the rotate portion get poor quality. This a take of the problem:
I used cairo PNG as output. Max quality in video and antialiasing of 2.
No, it isn’t a noise. And I have to say sorry, I should describe in a more clear way. In fact, Genete and I asked you to post your right png image so that we can compare them and figure out the issue. But anyway, you just solved by yourself.