Cleaning up motion blurred reflections

[Wilyman]

Hi,

I'm trying to get some nice highlights on spinning wheels, similar to this kind of thing...





The principle of lighting the scene to get that kind of effect is no problem, but I seem to end up with extremely noisy highlights, and I'm unsure which settings I need to concentrate on to clean them up...




I've got my geometry samples for the motion blur set to 12 and noise samples to 0.005, with cubic AA.
Is there anything I can do to smooth out the highlights and stop them looking so jagged and broken?

Cheers,

John

[kosso_olli]

John, I have found no solution to this as well. I made some thread here over at the forums, look here:
https://forums.chaosgroup.com/forum/...moving-objects
https://forums.chaosgroup.com/forum/...n-bokeh-shapes


One option is to clamp the HDRI for the reflection, but this of course reduced the intensity of the highlights.
I hope there is something that can be done about this. By the way, progressive sampler seems to handle this better then bucket.

[Wilyman]

Thanks Oliver.

I hadn't seen either of those threads, so they made interesting reading.

One option is to clamp the HDRI for the reflection, but this of course reduced the intensity of the highlights.

In this case, it's not a bright part of an HDRI that's causing those highlights, but a single VRay light that I've added for the very purpose of getting the highlights.
I'm getting slightly better results after increasing the geometry samples to 64 (!), but any higher and my render just sits on 0%, which I assume is because I'm running out of memory.

I hope there is something that can be done about this. By the way, progressive sampler seems to handle this better then bucket.

I'll give it a try. Never used the progressive sampler in over 15 years of using VRay, so probably about time I had a look!

Cheers,

John

[kosso_olli]

I'm getting slightly better results after increasing the geometry samples to 64 (!), but any higher and my render just sits on 0%, which I assume is because I'm running out of memory.

Did you do this in the general camera settings or just for the wheels in the VrayProperties?

[Wilyman]

Did you do this in the general camera settings or just for the wheels in the VrayProperties?

Just for the wheels. and only for the two that are visible. Everything else is set as low as possible.

[kosso_olli]

Just for the wheels. and only for the two that are visible. Everything else is set as low as possible.

Oh, wow. I'm out of ideas, then.

[^Lele^]

You may have some luck making the speculars a bit broader and softer.
It would be great if you could send the spinning rim and light to support however.

EDIT: while the above helps, also ensure that you have a min AA of 3/4 subdivs at least. While it will be oversampled easily later on during the rendering, it will provide for a better "bedding" to the sampler, making it find detail it'd otherwise miss.
below, samples illustrating what i wrote about above.
From left to right: the scene setup (notice the geo has very fine chamfers on every edge, not quite visible at that resolution), default settings, and a glossiness of 0.95, default settings, and gloss of 0.85, 4/24, and gloss of 0.85, and a crop of a 4-100, 0.01 NT of the problematic areas.
The Geo has 16 moblur samples, and performs 10 whole revolutions (3600 deg.) in 25 frames, while the arealight is at default values..

[Wilyman]

You may have some luck making the speculars a bit broader and softer.
It would be great if you could send the spinning rim and light to support however.

I can't send that particular one, but I'll try and make something similar with another wheel and send it over.

Cheers,

John

[^Lele^]

It took me a while to prepare the samples, did you manage to try any of the two methods out, or they didn't help?

[Wilyman]

It took me a while to prepare the samples, did you manage to try any of the two methods out, or they didn't help?

Thanks for all the samples Lele. Much appreciated.

Regarding the subdivs, I'm already on min 4, max 80, as with min set below 4 I'd occasionally end up with completely black buckets here and there.
Would there be any more benefit in raising either of them further?

As for softening the speculars, I'm giving it a try at the moment, although the original material was a VRScan, so I'm having to substitute it for a simple glossy reflective VRayMtl now.
It's only part rendered, and it does look cleaner, but the highlights are far broader than I'd ideally like them. I guess maybe I can counter that with a smaller lightsource though, so I'll keep experimenting.

Cheers,

John

[kosso_olli]

^Lele^ : I sent a scene file over to you. Feel free to fiddle around with it to get the result shown by John at the top with the red car.

[^Lele^]

Thanks for all the samples Lele. Much appreciated.

Hihi, that came out wrong on my side, i meant it as "sorry it took me a while to post the stuff." XD

kosso_olli thanks, will do!

[^Lele^]

So, it seems that for the while, the only way to properly clean up these kind of situations, without changing the scene setup, is with brute force camera sampling.
Namely, a 4-1000 (one thousand!) will render Olli's highlight perfectly fine to a noise threshold of 0.01, while not really taking any longer in the rest of the image which will never reach 1 million cam rays per pixel to achieve the given N.T..
Because of the very high camera sampling needed across the whole screen (the spinning wheel covers it all, there are no non-moblurred pixels), you will be able to shave some decent time from the rendering by lowering MSR to, say, 2.
I heard from a bird specific improvements are being studied, but this should work just fine, with minor variations, across most cases (f.e. with a slightly higher min AA, with a default MSR, and so on.), for the time being.

It goes without saying that this can be helped by lowering the intensity of the highlight in question (f.e., to 2 or 3 float, from 15-20. By whichever means.), which will shave potentially a great amount of time from the rendering.

EDIT: i should hasten to add that the sampleRate RE is your friend: if it shows red, there will be noise left in the image because max sampling has been reached before the noise threshold.
EDIT #2: below, a comparison of the original scene settings (1-32, 0.01) and the new ones (4-1000, 0.01) (left column) and the respective samplerate render elements (right column).
It took a *very* long time, however, in the parts which needed it, and are green in the Samplerate (green at 1000 subdivs. geez. XD).
Bright side? it resolved them exactly, and didn't take much longer elsewhere.

[kosso_olli]

Lele, can you please ping back the scene to me for testing?

[^Lele^]

kosso_olli Yes sir!