Historically, Pixar's RenderMan defaulted to a 2x2 Gaussian filter [1], and from what I can see, that hasn't changed [2]. Essentially it uses a truncated isotr

Historically, Pixar's RenderMan defaulted to a 2x2 Gaussian filter [1], and from what I can see, that hasn't changed [2]. Essentially it uses a truncated isotropic (non-separable) Gaussian defined by exp(-2.0 * (x*x + y*y)) with a 2x2 pixel support [3], which is slightly soft and completely avoids ringing. Gaussian also plays very nicely with filtered importance sampling [4] since it has no negative lobes. (Though I remember a number of studios using RenderMan preferring filters with a bit of sharpening.) [1] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 [2] https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering [3] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=207 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=20... [4] https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=d5d120ae2c47e38fc4a2d379cfcf9953f5e23ada https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&d...