Jagged aliasing on very bright objects

[tricky]

I regularly use sweep objects to create strip lights, applying a vraylight material to them. Doing this usually leads to jagged, non-aliased edges. Normally we do a lot of post work on our images, but my current project relies on 'click-render' results.

What's the best way to remove these?

I am using default colour mapping settings (Reinhard, Gamma 2.2, Multiplier = 1 and Bern Value = 1)

[alexyork]

It's an exposure issue. The easiest way that I have found to deal with this is to have your vraylightmat underexposed, so it doesn't blow out at the edges, render as normal, and then use a very simple channel in post to fill it with white. I know you said you need out of the box results though, so maybe someone else can jump in, here...

[Vizioen]

I regularly use sweep objects to create strip lights, applying a vraylight material to them. Doing this usually leads to jagged, non-aliased edges. Normally we do a lot of post work on our images, but my current project relies on 'click-render' results.

What's the best way to remove these?

I am using default colour mapping settings (Reinhard, Gamma 2.2, Multiplier = 1 and Bern Value = 1)

I don't like to do this anymore but try to turn on clamping and play with the value. Or you could also try and lower your burn value and bring back contrast with an S curve.

[vlado]

Enable Bloom in the V-Ray VFB and adjust until you get better AA without affecting too much the rest of the scene.

Settings that I find that usually work is something like Weight 15, Size 15, Shape 40. The goal is to have just enough spill of a few pixels around the bright objects that fixes the AA. This simulates quite well what happens in the real world too.

See the attachment for some examples.

Best regards,
Vlado

[tricky]

Enable Bloom in the V-Ray VFB and adjust until you get better AA without affecting too much the rest of the scene.

Settings that I find that usually work is something like Weight 15, Size 15, Shape 40. The goal is to have just enough spill of a few pixels around the bright objects that fixes the AA. This simulates quite well what happens in the real world too.

See the attachment for some examples.

Best regards,
Vlado

Oddly enough I have just started playing with this and it does help a bit. I will continue...

[tricky]

Those settings haven't really helped that much. I guess it depends on the vraylight brightness and pixel render dimensions, correct?

[vlado]

Yes, of course; for your scene the settings may have to be different, depending on the brightness of the lights.

Best regards,
Vlado

[Macker]

Vlado, my understanding is that this is an inherent with most render engines? I remember having the same issues in Mental Ray and it was because the computer struggles to antialias floating point values over 1, or something along those lines?

[tricky]

I guess my vraylight materials are too bright as in order to have anything like the right kind of softness, the entire image goes a bit too soft. I don't really want to dim the vraylight materials very much as they are giving the desired result in my render.

I will persevere but time is running out on this project.

[joconnell]

Those settings haven't really helped that much. I guess it depends on the vraylight brightness and pixel render dimensions, correct?

Yep you're right. The major problem is that anti aliasing is attempting to make a smooth transition from one object to the next along it's edge. If we stick with brightness only values for our pixels (lets pretend they're grayscale float values - 0.0 is black, 1.0 is white, 10.0 is super bright) then the anti aliasing filter is going to try and make some blending pixels along the edges to more gracefully go from a light to a dark value. If you've got a 1.0 pixel beside a 0.0 pixel and you want to anti alias the edge, it'll probably just be a case of finding the average between the two, so (1.0 + 0.0) / 2 = 0.5 or a middle grey, all good. If you've got a 2.0 bright pixel beside a 0.0 pixel then again you get (2.0 + 0.0) / 2 = 1.0 or normal white. If you've got a 10.0 pixel beside a 0.0 pixel the same thing again leaves you with (10.0 + 0.0) / 2 = 5.0. Our problem with the renders is that 1.0 white is pretty much the brightest we can show on a normal monitor, so if you've got a really bright object beside a dark object and again due to your pixel res you've only got 1 pixel to blend them, you could end up with a blending pixel that's correct from a rendering point of view, but it's still over 1.0 bright so it'll give you a very crisp, blocky look.

So what can we do? Either soften the transition in some way or try to tone map the render. So if you use a softer anti-aliaser such as quadratic or video, the edge transition between light and dark are spread out over more pixels so rather than us just having a single blend value, we've got more gradual steps which gives us a less harsh transition. A 2.0 bright object beside a 0.0 bright object now gets 2.0 / 1.33 / 0.66 / 0.0 so we're now starting to get a few blending pixels that aren't clipped in our normal white to black image display range.

The same thing can be done as Vlado suggest with some bloom. It happens in pretty much ever photo with the atmosphere catching reflected light and putting a tiny bit of a haze on highlights. It's kind of like the same blurring / softening trick that we'd do with anti aliasing, except this time it's more localized to highlights which is our problem area anyway.

The next thing we can do is limit the brightness of our pixels to give vray an easier time of it. If you use any of the clamping controls like max ray intensity or the clamp option in colour mapping you can cut off the really bright values in your scene. Admittedly this makes things a bit duller in your reflections and overall drops the brightness of your scene, but trying to get smooth anti aliasing between a range of 10.0 and 0.0 is going to be way harder than if you'd cut off the values at 3.0 instead. You'll still have enough brightness there to have bright whites but you'll likely have smoother highlights and reflections. Normal diffuse light is pretty soft so it's not that much of a problem on duller objects but reflective or specular objects get the full intensity of whatever they're reflecting and so give you huge values. The max ray intensity control only limits values for reflected light so you can keep your overall scene brightness but try and tame some of the really crispy bits in your reflections.

The last thing we can do is remap the entire image. Some of the colour mapping controls like reinhard allow you to treat the bright values differently from the mid and shadow values. If you were to use normal brightness, the bright values gradually come down, but so does everything else at the same rate. Reinhard lets you gradually bring down the bright values over 1.0 and rather than a really harsh linear colour correction, it'll gradually fade the change from the non affected to affected areas, so it's almost like a blurring effect on the brightness.

We get the same issues doing car commercials here - if you use a vray light the edge is quite harsh. On a real light there's a hotspot in the centre which gradually dims towards the edges away from the bulb so it creates a natural transition itself. The vray softbox texture lets you do this and in our case we use hdri's of light fixtures in our vray lights so the reflections have a bit of softening towards the edges naturally.

[joconnell]

Oh yeah, and in your case just gradually bring down your reinhard burn value and your max ray intensity. Try 0.5 or 0.25 on burn - you'll have quicker renders too.

[snivlem]

I think the best way to remove them is to render 32-bit float and clamp in post. If your tonemapper is capable instead of generating jagged edges it will bloom or glare this extreme difference between bright and dark and you'll get very nice images this way.

[samuel_bubat]

The easiest way is probably to turn on clamping and sub pixel mapping. But this can alter your shaders. For example materials where you want
drastical changes in brightness on pixel level. A Car shader for example. Also make sure you have the mode "Color mapping and gamma" selected
or it can result in a pretty bad overall anti aliasing. the shading of strong lights may differ. It´s not worse but different.
I usually work with both on. It´s not to much of a problem if it´s turned on from start of a project. Turning it on at the end of a project wheere everything is allready setup
and adjusted may result in differences as described above. Btw. I´m talking about Vray 2.4 using Reinhard. Don´t know if this is different in Vray 3

[stevesideas]

I think the best way to remove them is to render 32-bit float and clamp in post. If your tonemapper is capable instead of generating jagged edges it will bloom or glare this extreme difference between bright and dark and you'll get very nice images this way.

Do you know how you clamp brightness values in something like aftereffects ?

I've tried curves with a roll off on the whites but it doesn't work.