When it comes to rendering, there is always a tradeoff between detail and antialiasing. Filters play a big role in this.
I am a huge fan of the sinc filter – it’s sharp and enhances the detail beautifully. But this sharpness means that sometimes, it will produce an effect known as “ringing” – contrast-y bands on the border that separates brightly-lit areas from dim ones.
Using physically-based Fresnel attenuation of specular will often create this contrast when backlighting is bright enough.
We are often led to believe that upping filter width will create “higher quality” images, so we reach for the controls… and get an even worse case of ringing.
There’s a lot of maths involved behind the scenes, but suffice it to say that generally, if you see ringing you want to eliminate, you should do the opposite thing and turn your filter width down.
Here are a few renders – check out the highlight on Aiko3’s left ear and how the ringing, so jarring with the 6×6 filter width, gets less noticeable with filter widths of 4×4 and 2×2.
In this case, 4×4 apparently provides the best tradeoff between sharpness of detail and minimum artefacting.
Left to right: 6×6, 4×4, 2×2. (these thumbnails are clickable, make sure to check out the full versions!)
Although if you do not show anyone the sharpest image, people will often never know that you are “cheating” ;D