V-ray Next 4.30.02 - Extreme "dancing" white pixels on any material at a distance with glossy reflections

[Morbid Angel]

Lele, it seems there is some misunderstanding.

In the teapot file from post #59 the camera is moving.
In your file you uploaded in your last post, it is not. We know how to render consecutive frames with static camera without getting randomly placed highlights by now. The solution was proposed by Joelaff in post '33 by deactivating locked noise pattern:



His solution was confirmed by me in post #34, with an exception:



So, I opened the scene you uploaded today, animated the camera ever so slightly, and voila: Dancing highlights (i just set metalness back to 0, sun disc is disabled of couse):




If you could take a close look at that scene again to find a working solution, that would be great. For over a month now, I am not able to produce a sequence that is looking clean. I'm seriously running out of ideas. File is attached. Thank you so much!

teapots_olli_01.zip

setting the min subdivs to 10-15 should fix it. Honestly though you have to understand that sampling a bright dot from an hdr is no easy task for a raytracer. Objects also glint in real world too the further they are.

[Joelaff]

setting the min subdivs to 10-15 should fix it. Honestly though you have to understand that sampling a bright dot from an hdr is no easy task for a raytracer.

No doubt, which is why people often blur the HDR for such things.

Objects also glint in real world too the further they are.

True, but, sadly, that flickering almost never looks like what you get from VRay (or many raytracers), especially like the example above. The glinting in the real world is much broader, and hardly ever changes that much from frame to frame. In a slow moving render averaging frames together in post before applying some sort of bloom can help.

[kosso_olli]

I will try to disable specular contribution for the sun, and then placing a directional disc light to care for the specular. Hope it get's better this way...

[Morbid Angel]

Kosso_olli - what are your sample settings?

[^Lele^]

Sadly, a min subdivs of 16 makes no difference to the teapot scene above.
And it's a min amount that's not feasible for the kind of work Olli does: rendering most of his cars as fixed with high sampling would take forever.

[kosso_olli]

Here is the test with the specular disabled for the sun and an additional disc light far away.
It is fiddely to get the right position and appearance, but the render is clean.
However, if V-Ray could handle these situations out of the box, I would be very happy.

[Joelaff]

The fact that this trick works so well makes me wonder if the VRaySun couldn’t do something like this internally. In other words, rework the specular component of the VRaySun to have the option to adjust directionality.

I am speculating that it is the directionality because it’s not just the size, since you have to make the size of a VRaySun much larger than you have to make the extra VrayLight in order to get the same level of cleanliness in the render. (If, for example, you use a duplicate, larger VRaySun just for the speculars, rather than a VRayLight that VRaySun has to be very larger indeed to render cleanly. This was first thing I tried when developing the technique, and it did not work very well.) Also note that increasing the directionality of the extra VRayLight up much past 0.3-0.5 starts to cause the flickering speculars again.

Perhaps this issue is related to the same issue that causes VRayLights with high directionality not to be seen at oblique angles (especially through refraction). It looks like samples with the VRaySun have to be directly at the light (along the normal of the light disc) to be “seen“ by the samples. While this makes some sense for a VRayLight with high directionality (it’s akin to a real world light with a perfectly black “grid” — the typically black honeycomb light modifier you put in front of a real light), it does not make any sense with a sun, where you would always see the light itself.

kosso_olli mentioned it can be challenging to position the extra VRayLight used for the speculars. In this case I find parenting this extra VRayLight to the VRaySun made it relatively easy. You can then drag the light in and out along the vector to the target to set the distance. Of course you have to set the intensity based on the distance, or disable falloff (since sunlight hardly falls off over the radius of the Earth anyway).

[fixeighted]

So is this a choice of:

The Vraysun's calculations are physically accurate. Works in most situations. Deal with it (odd, to be sure).

Or:

If there's a need for no flickery shit (optimal, without even thinking about it, imho) then use a secondary light source which effectively is less punishing for the sampling and gives almost the exact same result.
(This is seemingly the result of this very long topic, though only got to rather painfully it appears)

[^Lele^]

The sun intensity works perfectly for GI.
It never was meant to produce highlights in the first place, which is also why the sun and sky system came with a custom sun option from the get-go.

[kosso_olli]

kosso_olli mentioned it can be challenging to position the extra VRayLight used for the speculars. In this case I find parenting this extra VRayLight to the VRaySun made it relatively easy. You can then drag the light in and out along the vector to the target to set the distance. Of course you have to set the intensity based on the distance, or disable falloff (since sunlight hardly falls off over the radius of the Earth anyway).

I did parent the disc light to the sun. But I had to figure out the order first, because weirdly the disc light is casting a shadow, even when set to invisble.
Also, you can not disable falloff for a VrayDiscLight.

[^Lele^]

It's indeed better to use a simple, old directional light from max (with v-ray shadows).
Granted, the speculars won't be area ones, but the whole exercise is to avoid the hard sampling a minuscule are light would induce, and a point light does not.

[Joelaff]

Also, you can not disable falloff for a VrayDiscLight.

Oh yeah. That was removed a version or two ago.

It's indeed better to use a simple, old directional light from max (with v-ray shadows).
Granted, the speculars won't be area ones, but the whole exercise is to avoid the hard sampling a minuscule are light would induce, and a point light does not.

I find those speculars too artificial / 90s looking, hence the disc.

But the VRaySun, being designed as a Sun, should produce the correct highlights without the sampling issues.

I am curious if the developers have any thoughts on my hypothesis regarding the directionality of the VRaySun impacting the specular sampling ? It's clear they have already put a special case for the visible sun disc to make sure it is not attenuated off angle like a VRayLIght would be with a high directionality. If directionality is the issue (not 100% sure, mind you) then perhaps they could tweak it for the speculars.

[^Lele^]

I find those speculars too artificial / 90s looking, hence the disc.

If you can show me an appreciable difference between the speculars of a 0.5 degree arealight and a pointlight, you win a prize.
The whole issue with sampling the sun disc is that it's so small to not be good enough to integrate as an arealight in the first place: if it was big enough, we'd get area speculars instead of glints.
When the highlight gets to sub-pixels sizes is when the issues appear, and also when it's impossible to tell the difference with anything else (as everything resolves to the resolution limit of the pixel.)

But the VRaySun, being designed as a Sun, should produce the correct highlights without the sampling issues.

No, you assume it should, but it's never been the case, with any modern raytracer (the old ones never had these kind of energies to deal with.).
What the sun does is to produce the correct energies for GI, and carries from day one the means to exclude it from the part of calculations that don't suit it (zero the specular/reflection contribution. It used to work as one with hiding the disc, it's now split better, so a different toggle.).
On the sun, and in the sky map (with the custom sun node.).
Should the sun do more to ameliorate this stuff? I think so: it should be clearly written in the docs (which are very old, and with wrong info.).
Anything more would take control away from the user, control that's been there from day one.

Worry not, the devs are reading here.

[Joelaff]

Perhaps if you are making your sun that small then there is not much difference between the area and the parallel light. In the world of photography and cinematography were rarely use the sun completely unmodified, preferring subtly softer highlights. So even on a January day at noon I would still want a slightly softer highlight. Also, keep in mind the sun still has a lot of energy around the disc itself in terms of scattering in the atmosphere.

I still stand by the statement that it should produce correct highlights without flickering, regardless of any whataboutism regarding any other software.

[Joelaff]

Also note the almost perfectly round highlights in the bottom image vs the more oblong and smoother highlights on the top image.

The bottom one looks like phong highlights from the early 90s. Granted some tweaking to the glossiness and GGX tail, and/or a clearcoat* could help if this really was your final image.





* “Yeah, but what about that TruCoat?”