There is this issue 322116 https://bugs.launchpad.net/bugs/322116 "PDF export does not use the highest quality for rasterized filters" The reason for this issue is that each nr_arena_item checks the preferences for the filter quality even for off screen rendering.
This is wrong behaviour.
During png export there is a sequence like this save, set ... rendering ... restore. This changes for a short moment the preferences.
This is also not good style. (remember a background task renderin to png - in future)
I developed a patch that is attached to the issue in launchpad.
Attached patch puts render quality properties to nr_arena. You can do now "nr_arena_set_renderoffscreen(arena)" for an offscreen arena in order to get highest accuracy.
please review!
Adib.