Moving from Corona to Vray Questions

[Donfarese]

Hi,

We do a lot of animation, while we love Corona I've been told that Vray is much faster for animation. I haven't used Vray in quite some time, but tried the Demo version and have some questions before we decide if we will move over to Vray. I must say Vray has come a long way, things are looking really great now. I'm really interested in the Vray GPU also, for speed and local inhouse renderfarm. But of course right now it's impossible to get a videocard, let alone multiple RTX 3090's. So we are running Threadripper 3990x's which are fast.

1) Samples - Trying to compare speed of Corona and Vray. So far my renders are rendering faster in Corona. But I'm sure my settings are not 1 to 1, and I'm messing up the comparison here. In corona you have just "Noise Level Limit" compared to Vray where you have "Noise Threshold" and "Min / Max Subdivs". So trying to get the renderers as close as possible, I thought Vray 0.03 Noise Threshold was equal to Corona Noise Level Limit of 3.0%, but that doesn't seem to be the case. What are good setting to compare each? This will help me because I know what settings I use in Corona for final quality, so to be able to transfer over to Vray will be great.

2) Displacement - In Corona right in the main material we have settings for displacement. You can set the min and max level in actual units, can you do this with Vray? We use this with almost every material, so objects with multi materials like trees can have displacement on just the trunks. How is this accomplished in vray?

3) Albedo - In corona you have a Albedo render element so you can check that the Albedo isn't to high. We purchase a lot of models and can't tell you how many times one of them has a material with to high an Albedo and it makes the render engine take forever. Having that Albedo render element is priceless to checking and fixing the scene quickly.

4) Denoising - I noticed the Vray Denoiser denoises the background HDRI, is there a way to stop it from denoising the background image?

5) Converter - I use the Corona Denoiser constantly, it has great interface and options and converts vray scenes over to corona like 95 - 99% perfect. But the Vray converter doesn't have much options at all and does frankly a pretty terrible job of converting Corona over to Vray. Is there a better way of converting? Is this to be updated?

6) Adjustment - In corona I can set the MSI down from 20 to 4 and the Sampling balance > GI vs AA Balance down from 16 to 8 and get much faster renders. I tried reducing MSI in Vray but it didn't speed up render much if at all. What are setting that would increase speed but still keep quality in Vray?

[hermit.crab]

Answers to your questions:

1. I am not sure. I would need to ask the Corona team how to accurately compare their percentage value to V-Ray's value. I'll write again with my findings.
2. The VRayMtl's displacement option is controlled through the Default displacement options (Render Setup>Settings>Default Displacement). For a more refined control, the VRayDisplacementMod modifier is applied to the object. If only certain elements need to have displacement, UVW unwrapping on a specific map channel is also an option.
3. There isn't an Albedo channel in V-Ray. This forum thread may provide additional information.
4. No, I'm afraid. You can easily mask it with the Alpha channel in post, however. Or use a Background image in the VFB2 if possible.
5. The V-Ray scene converter is the way to do it. Not all node conversions are supported, however, they will be updated in future builds. Here is a list of supported conversions.
6. I presume MSI corresponds to V-Ray's Max. Ray intensity and Sampling balance is VRay's Min. shading rate. Thing is, with those options, namely Min. Shading rate, you simply transfer the loss of quality to another component of the rendering. You do not retain the same quality even though it may seem like it. This depends on the amount of GI vs AA that needs to be calculated for a given scene. To hasten a rendering, raising the noise threshold and adding a denoiser should do the trick. Or use the progressive image sampler to stop a rendering whenever necessary.

EDIT: Regarding point 1 - I've discussed the question with the Corona team. The noise threshold in V-Ray and Corona are completely different measuring values and cannot be directly translated to one another, hence an absolute comparison is impossible. You may try comparing the render defaults or experiment in your own way for your desired result.

[^Lele^]

1) Samples - Trying to compare speed of Corona and Vray. So far my renders are rendering faster in Corona. But I'm sure my settings are not 1 to 1, and I'm messing up the comparison here. In corona you have just "Noise Level Limit" compared to Vray where you have "Noise Threshold" and "Min / Max Subdivs". So trying to get the renderers as close as possible, I thought Vray 0.03 Noise Threshold was equal to Corona Noise Level Limit of 3.0%, but that doesn't seem to be the case. What are good setting to compare each? This will help me because I know what settings I use in Corona for final quality, so to be able to transfer over to Vray will be great.

Matching settings would also mean setting up identical indirect clamps, and matching V-Ray's MSR to Corona's GI vs AA samples.
They'd still not match 100% (ever), but they'd then be close enough.
You'd still be unable to change russian roulette rejection and other such hidden parameters, which make a ton of difference on how the sampling of a render progresses (f.e. tracing quicker, but rejecting more, needing more passes, etc.)
Both engines will take different sampling strategies behind a user's back to ensure good quality, so more rays than set are often cast by both.

2) Displacement - In Corona right in the main material we have settings for displacement. You can set the min and max level in actual units, can you do this with Vray? We use this with almost every material, so objects with multi materials like trees can have displacement on just the trunks. How is this accomplished in vray?

Set the displacement modifier up, and then set it to use the material.

3) Albedo - In corona you have a Albedo render element so you can check that the Albedo isn't to high. We purchase a lot of models and can't tell you how many times one of them has a material with to high an Albedo and it makes the render engine take forever. Having that Albedo render element is priceless to checking and fixing the scene quickly.

You can have a decent approximation of Albedo by plussing the diffuse filter and the reflection filter.
You'd need to measure the values yourself, however, to find which exceeds 1.0.
It's a very easy trick to pull in both nuke and fusion with a simple expresison node, no idea about Photoshop, however.

4) Denoising - I noticed the Vray Denoiser denoises the background HDRI, is there a way to stop it from denoising the background image?

If the image is a backdrop (not a in a dome, in other words) you ought to be able to at least prepare yourself a denoised RGB and a straight Background to be output from the VFB, via the composite (RGB-background and denoise.).

5) Converter - I use the Corona Denoiser constantly, it has great interface and options and converts vray scenes over to corona like 95 - 99% perfect. But the Vray converter doesn't have much options at all and does frankly a pretty terrible job of converting Corona over to Vray. Is there a better way of converting? Is this to be updated?

It'd help a lot to know what you think is done poorly, so to improve it where possible (as usual, not everything matches 100% in conversion. CGI should have the subtitle "lost in translation").

6) Adjustment - In corona I can set the MSI down from 20 to 4 and the Sampling balance > GI vs AA Balance down from 16 to 8 and get much faster renders. I tried reducing MSI in Vray but it didn't speed up render much if at all. What are setting that would increase speed but still keep quality in Vray?

What Alex said.

In both engines, changing those values will simply cast less secondary rays (generally cheaper) but more camera rays (generally more expensive).
As all the secondary rays are cast before another camera ray is, reducing secondaries simply speeds up the passes of camera rays.
For the same noise level, you'll then have gotten a better geometric AA, maybe, but at the expense of much longer renders.
Conversely, raising MSR means subtracting from the camera rays' job of antialiasing geometry.
Big, flat areas will be cleaner sooner, but the price to pay to antialias the fine details will be enormous, meaning the image will actually converge later.

We decided on a value of 6 by default because by our measured estimates is the best compromise for the kind of engine V-Ray is.
We suggest to only ever change Noise Threshod, and in some case also min AA.
If doing animation, then picking the right preset for the LC is the way to go (i.e. no precalculated stuff).

[Donfarese]

Thank you guys for all the info. Will keep doing inhouse testing.

[kosso_olli]

You'd still be unable to change russian roulette

Is there Russian roulette in V-Ray?

[^Lele^]

been there a few years.

[kino_unico]

is there any comparison with the results with a similar noise?

[^Lele^]

Similar, sure.
Identical, no.
And the difference, for even minute values, is potentially big: not all noise is created equal, and the work done to clean it can vary immensely.
My suggestion is that one should work with what one feels most comfortable with, as more work will get done that way, rather than trying to shave minute amounts of time off this or the other engine.