Color texture affects reflection roughness/glossiness?

[tennet]

Hi,

Why is the texture map used in the 'color channel' affecting the reflection glossiness/roughness of a material? If I set the roughness of a 'Physical material' to be very matte, just using the slider and no textures for the roughness channel, then I'd expect the material to have the same overall roughness.. but it hasn't. See attached screenshot.

Not sure if I use the PBR material in the wrong way, but for example, if I'm rendering a product and I want it to have a printed artwork. I want the artwork to have the same surface finish everywhere (same roughness/glossiness), even if it has many different colors.. How should I achieve this using the 'Physical materials'? (I know how to do it using the Legacy Materials, but I want to try and use the PBR materials instead).

I use Cinema R21 and Corona "Version: 7.0 rc 5".

Any help is appreciated. Thanks!

[TomG]

Whatever you are looking at, I doubt it is roughness getting changed by the base color :) Why are you using a Release Candidate, when Corona 7 is up to hotfix 2? RCs are only for use during development, and should be hastily abandoned as soon as a final is out. Our first suggestion then is install 7 HF2 and try that (RCs being in development may have bugs, that get solved before release, which is the purpose of an RC :) ). If the issue persists with the current up to date release version, sharing the scene (or any scene where this happens) would be good so we can have a look at everything, from the geometry to the lighting to the end result.

[tennet]

I don't know! 😅 Thought it was the latest version I had installed. Downloading the hotfix 2 now and will try another render. Will update here if it fixes the problem. Thanks!

(the image I posted before was the reflection pass of a render ONLY using a color texture and a high roughness value with no other textures (Physical Material).. so in that render I believe the glossiness was affected by the color map, but hopefully it will render correct now when using the correct version)

[tennet]

Hi again,

I've now tested this further with "Corona version 7 / Hotfix 2" installed. Attached are some screenshots showing the problem + a very basic scene where I've created two different lighting setups for you to test. I think I have found something that triggers this.

- The first lighting setup uses 'Corona Area Lights' only and this seem to render OK without affecting the reflection pass/roughness values.

- The second lighting setup though (which is the way I prefer to work) uses 'Corona Light Materials' with HDR textures applied to simple planes. As soon as I turn on the HDR lights (and disable/hide the area lights) then the color map used in 'Base layer color' is starting to affect the 'reflection pass' (the rougness value). You can see this in my screenshots that there aren't any other textures loaded in the scene, so the reflection pass should be clean here. It is when using the Area lights setup.

I believe this must be some sort of bug since it only seem to affect renders using the HDR lighting textures, but if I'm just doing anything wrong please let me know.

Many thanks!

[maru]

I was able to find some old reports about this in our internal systems. It is either a very old bug, or something expected.
Here is one of the dev comments about a similar issue, just the other way around - the diffuse pass is affected by reflections - and it suggests that this is indeed expected:

This is expected. This render element returns the diffuse part of the material. If reflection or IOR is increased more light will be reflected and thus diffuse component will be lower/darker.

(Internal ID=179407838)
(Internal ID=179407732)
(Report ID=CRMAX-799)

[mmarcotic]

Hello,

can you supply us with the testing scene as well?
https://corona-renderer.com/upload

Thanks,
Jan

[tennet]

Hi Jan,

The ZIP-file above includes the test scene. But I have now uploaded the same scene via the Upload page you linked to. Many thanks for looking into it, looking forward to your findings.

Best,
Frederik

[tennet]

I was able to find some old reports about this in our internal systems. It is either a very old bug, or something expected.
Here is one of the dev comments about a similar issue, just the other way around - the diffuse pass is affected by reflections - and it suggests that this is indeed expected:

This is expected. This render element returns the diffuse part of the material. If reflection or IOR is increased more light will be reflected and thus diffuse component will be lower/darker.

(Internal ID=179407838)
(Internal ID=179407732)
(Report ID=CRMAX-799)

I'm not sure what it means if it's "expected" (correct behaviour or a problem that needs a fix?), but when using the multi-passes for post-work then I find it to be a problem if my 'reflection pass' has information imbedded that shouldn't be there. For this particular example I'm working on a product that will be updated with many different artworks. If I had a clean 'reflection pass' rendered (without any roughness data added from the color map) then I could use the same reflection pass for all the artworks when retouching the images later, which would save me lots of time. Hope you can fix this!

Thanks,
Frederik