HDRI Map for reflection create shadow

[notoriousbug]

Hi, I would like to create interesting reflections in this model then I added a hdri map in the reflections channel. Is it correct that this map creates shadows?
What I would like to achieve is a lighting obtained from Corona Sun and Corona Sky so that I can correctly position the position of the sun and thus the projection of the shadows and separately have a map that only generates the reflections..
I have tried turning off Corona Sun and Corona Sky leaving only the hdri map that I put in the reflections channel but I see that it generates shadows for me

Sun Off (Only HDRI in Reflections slot - Sun and Sky Off)


Sun On (Sun + Hdri in Reflection slot - Sky Off)


Sun + Sky + Hdri


Sun Position



thnks
Not

[romullus]

Did you try to render with reflection override off and compare with what you have now? There must be some other light source in your scene - if you turn sun and sky off, the scene should render mostly black, except for highly reflective surfaces and definitely there should be no shadows.

[notoriousbug]

hello, thank you very much for your reply :)
Yes, I had already tried the various solutions as well which I send below for you to see

Only Corona Sky


OFF (Sun, Sky, HDRI)


Only HDRI Refl. override



(Render hidden lights is off)

Not

[notoriousbug]

Without material except for sphere

[romullus]

Without material except for sphere

That doesn't look normal to me. Can you do one more test - render with material with zero reflection override (reflection - 0 if it's legacy material, or IOR - 1 if it's physical). That would make absolutely obvious that we're seeing lighting and not specular reflection here.

[maru]

I can see that you are using Corona 12 Update 1 Hotfix 1. Can you please try the same thing in Corona 12 Update 2? https://my.chaos.com/download/build?product=Corona&platform=3ds+Max
There is a fix in Update 2 which should help exactly in this case.

[notoriousbug]

@Romullus
I think you were right..it seems something related to reflection in fact, doing as you told me (I set to 1.0 IOR of the Corona Phys Material seems to solve it..)
I then did some tests with the original hdri and a second copy where I eliminated the strong intensity generated by the sun..I simply cloned the neighboring area..I don't know if that is correct as a method..doing so though, replacing the map with the new one without the sun the reflections come out completely different (very noticeable the difference on the car bodies)







@Maru
I will immediately try to install the new version

thank you all

[romullus]

Yeah, but it shouldn't look that way. Those results are simply wrong. I tested similar setup myself and it's clear that there's diffuse component present when there shouldn't be any. I guess that's a limitation of non-physical hacks, which environment override surely is. Mind you i'm on Corona 12U1H1 and it's possible that this was fixed in Update 2 like maru suggested, so it's worth updating and test again.

BTW, i find that if you go in to developer settings and change lights sampling mode from default MIS to BSDF, then diffuse component mostly gone, but result is ugly, so i'm definitely not suggesting doing so.

[notoriousbug]

very kind @Romullus
I have updated to Hotfix version 2 but the result is identical unfortunately..
Continuing to test..I found that the problem is created when increasing the Output Amount value or when lowering the Gamma value..
I need to modify it to give more strength to the reflections because if I leave both default values at 1.0 the reflections are non-existent..

[romullus]

Increasing output is simply equalizing HDRI intensity with Corona sun and sky. It has nothing to do with the issue. You can get the same result with output 1 and reduced sun and sky intensity (of course you would also need to adjust camera exposure to see anything in that case). The problem is that you want to use HDRI for reflection override, which is a non-physical hack and Corona hates that :] IIRC one of the suggested solutions would be to use low dynamic range image LDRI in environment overrides, but of course reflections would look terrible in that case. I personally would suggest to ditch overrides and build simple environment around your scene. It don't have to be detailed, might be just a simple planes with textures of trees, buildings and what not. As long as they are not directly visible in the camera and your scene don't have giant chrome sphere in it, this method should be good enough to fool viewer into thinking that the environment is real. Most importantly you wouldn't have any issues with fake shadows that way.

[maru]

I was able to reproduce this and logged it for our developers as (Report ID=CMAX-1623). I am afraid, as Romullus explained, this is yet another light transport "bug". Currently, I can't offer any workaround other than either fully removing the reflection override or clamping it to 0-1 range (using a low-dynamic range image rather than an HDRI). I will be sure to report back here once I have any useful info.

[notoriousbug]

as always thank you all for your kindness :)

[Renovacio]

Yes, this has been a problem for a long time. I am converting hdri to jpeg format in photoshop. And then no shadows are generated.