Aliasing problem when rendering lights...

[Njen]

(Lot's of questions from me today as I ramp up in the lighting/lookdev portion of my animated short film - www.cyan-eyed.com)

I am experiencing aliasing issues when I produce a render that has a Corona light in it (or a material with a bright Corona Light material). If I expose the image down so that the light has a value of less than 1, I see nice looking anti-aliasing, but at an EV of 0, I get the telltale 'jaggies'. It almost seems to me when doing my own tests that the current order of math is to sample the light colour then multipliy by the alpha of the light, then multiply the result by the intensity of the light. Or am I making completely wrong assumptions?

[erkuttaner]

Maybe this helps
https://www.youtube.com/watch?v=Wc9aaA6WAuQ

[Njen]

Nope, it's not the same issue, there isn't any geometry too close to each other, it's just a light.

[Njen]

FYI for reference, this is the same image as above, but exposed down 10 stops. Nice beautiful anti-aliasing.

[maru]

Nope, it's not the same issue, there isn't any geometry too close to each other, it's just a light.

It seems to be the same issue - neighboring pixels with huge contrast difference. The solutions suggested in that video should work here too.

[Njen]

Yes it's high contrast pixels, but that video doesn't help. The image I posted was rendered with over 250 samples. Plus I don't want to clamp the light, or else I would lose information I need to be able to properly comp the image. I've used other renderers where this isn't a problem.

[Njen]

I just did a test using the ART renderer (which I have never used before until now), and the aliasing is much better than Corona when rendering a light. The pixel spread of the anti-aliasing of the right edge of the ART light is more than twice as wide as the Corona light.

[Njen]

Followup note: to be fair to the above test, ART is using a pixel filter of 3, where as Corona was using a value of 2, so I did another test, with a value of 3 in Corona, and it still didn't look as anti-aliased as ART, but a little more than in the above image..

[maru]

One more solution (although not always possible...) is rendering an image in higher resolution, and then reducing it in post.

[Njen]

Unfortunately, I am rendering an animated short film, and at this point am unable to spare much more of my meagre resources :(

[sebastian___]

A potential solution would be to add glow/bloom. Since a strong light source or a very white surface should have bloom anyway.
On a black background maybe it looks too strong, but in the second pic I added you can see that on a normal background the bloom would not be as noticeable (in case you don't like bloom).

[Njen]

For the greatest level of control, I do all comp in comp, not in the render (I have no use for Corona's post effects). I will test to see if I can get a tight glow to look any good with the aliased light in comp, though obviously even if this works, it's just a temporary bandaid fix :D

[Ludvik Koutny]

Glare in latest corona (daily) version resolves exactly this problem. It has that exponential falloff that will give you smooth edges without need to have lots of visible glow/bloom around your light source. In the regular scene without black BG, you will barely notice it. (Just make sure not to leave ray blur at 0)

[alexyork]

Maybe the blur value should not be able to be kept at 0, to avoid problems.

[Ludvik Koutny]

Maybe the blur value should not be able to be kept at 0, to avoid problems.

It doesn't really cause any problems. Sometimes, under certain conditions, you can indeed get quite sharp glare. It's just that if you want to use glare primarily to cover up aliasing around bright spots, but don't really want to have obvious glares on your image, then you just crank up blur to make sort of bloom out of that :) And such a bloom then gets quite unnoticeable.