IPR vs final render

[craigdvance]

Need HELP!
I have been working with the scene for a week, rebuilt it multiple times. The issue is I cant get parity between the viewport render and the final render. The final render is always brighter.
Working in Maya with the latest build of V-ray 5
Windows
Happens with both progressive and bucket renders.
Not distributed rendering.

[Muhammed_Hamed]

This happens because the IPR only use 5 GI bounces, on the other hand production rendering uses 100 bounces (with LC)
For this to match, you will need to up the GI bounces in the IPR tab to 16 maybe.. it should be closer this way

And if you use Auto exposure or Auto white-balance .. these don't work in the IPR, because they rely on LC (IPR always uses BF/BF)

[craigdvance]

Thank you, if I set to Brute Force and adjust the bounce rays, I can get what I want. with LC it seems no matter how adjust the subdivision it never changes or updates.

[dougWilkinson]

its worth mention that the light cache is closer to the "correct" result in terms of photorealism. But i agree the difference between the IPR and final when using the defaults is quite different sometimes. Its not just GI there are other differences that are noticeable like SSS materials.

[craigdvance]

just some screen caps. Bruteforce acts like you would think, changing rays and lightening and darkening but Light Cache I can get no change.

[Muhammed_Hamed]

Thank you, if I set to Brute Force and adjust the bounce rays, I can get what I want. with LC it seems no matter how adjust the subdivision it never changes or updates.

It is important to note that LC subdivs don't control the amount of bounces here
The LC bounces are set to 100 by default, it was possible to change this in Vray Next.. then it was removed in 5 (Pro tip, don't play with LC settings.. there is just no need to)
But again, the realistic result is LC like what Doug explained above.. you gonna need like 16 BF bounces to get something close

[Muhammed_Hamed]

We might see LC in Vray's IPR in future(at least for the GPU engine) it is what the devs talked about so far.
This is gonna be helpful as the IPR will be matching final rendering, and it is gonna be so much faster (making use of all the adaptive stuff that relies on LC)

in Vray for 3Ds Max, LC works in CPU IPR.. and is really great, specially for interior scenes. All other Vray plugins will use BF/BF for IPR

[seandunderdale]

its worth mention that the light cache is closer to the "correct" result in terms of photorealism. But i agree the difference between the IPR and final when using the defaults is quite different sometimes. Its not just GI there are other differences that are noticeable like SSS materials.

Thats interesting....I thought it was the other way around. Is it just down to the amount of bounces or is there more to it?

[Muhammed_Hamed]

Thats interesting....I thought it was the other way around. Is it just down to the amount of bounces or is there more to it?

Yeah, it is about having more bounces. It is how light behaves in real life, and on another note the illumination of adaptive domelight is more physically accurate
Adaptive domelight will need LC to work,

[seandunderdale]

Its not ideal then, as you mentioned, that IPR in Maya uses BF. Results may vary switching to and from IPR and final render. I almost exclusively have been using BF/BF in CPU mode, and BF in GPU since the days the render time became affordable. I used to dread coming in to work in the morning to find my 8k car interior has LC blotches everywhere. BF fixed all that in a click if a button. I dont do any multibounce scandinavian white arch vis stuff so maybe I dont need it so much. Although I did see LC (hashmap) was faster on GPU, so thats one reason to use it as the studio Im at currently is all about GPU (For better or for worse)

[Muhammed_Hamed]

It only looks different mostly because of GI bounces
If you up the BF bounces to 16 for IPR the result is gonna be closer to final rendering.. Close enough for lookdev/lighting, this is how myself and many other people use Vray
I agree that this is not ideal, we need LC in IPR like 3Ds Max.. that would be great!

I almost exclusively have been using BF/BF in CPU mode

This is very bad ..
light cache is really the core of Vray's smart sampling/adaptivity .. It is a massive advantage in Vray's workflow and many features rely on it, like adaptive lights, adaptive domelight, Auto-exposrue, Auto white-balance...etc
We have used LC for pretty much every scene since Vray Next.
The difference is speed between BF/BF and BF/LC is quite massive.. it is not just double or triple the speed, in some of our scenes it is 7x and 10x faster with adaptive lights alone.. and another 2x-4x with adaptive domelight
This is also why Vray is so much faster than Arnold or Renderman for GI intensive interiors.

[seandunderdale]

Consider me a convert!

[seandunderdale]

I seem to get some buckets rendering the Light Cache differently to others in GPU CUDA / Hybrid mode in Vray Next. If I switch to Brute Force, these issues go away. Maybe its to do with my hardware, or drivers, Im not sure. Its things like this that made me switch to brute force on CPU in the first place. Sure, you might get a faster render with Light Cache, but in the morning your 10k car interior might be worthless. I never get problems with brute force, some when I have the luxury of an overnight render with free render nodes, Im likely to stick with Brute Force.

Ill test again without Hybrid mode and see what happens.

[Mihail.Djurev]

I seem to get some buckets rendering the Light Cache differently to others in GPU CUDA / Hybrid mode in Vray Next. If I switch to Brute Force, these issues go away.

This is certainly unexpected. Could you send a scene that reproduces the issue to support @ chaosgroup.com ?

[waaazoo]

this is why use so rarely IPR. I'm nearly always getting inconsistent results between IPR and production. I prefer to do my lookdev by rendering small parts of the image. It's a shame we can't just test everything in IPR (at least in Maya)