Bad Additive Reflections.

[wizlon]

Hi all,

I'm having issues with my standard VRayMtl reflections. Photography with glasses looks correct - Vray render is doing some weird additive thing. Reflections are much brighter than the object being reflected. How do I fix and make the reflections subtractive/physically correct?

Thanks all.

Lee.

[chuckie7413]

Maybe you could share your scene? Obviously doesn't seem right that it is reflecting brighter than the actual object but maybe it is something to do with how you setup your scene/material for for the ground.
Is the image you posted a raw render or something you comped together?

[wizlon]

Hi Chuckie,

I've attached a scene - thanks.

It's a straight beauty render out of Maya. In Mental Ray I used to use Zap's production shaders (mip_matteshadow) and set the reflections to subtractive for white/bright surfaces. This worked like a charm and looked like image 1 with the glasses.

Regards,

Lee.

[chuckie7413]

Hi Lee,

I looked at your scene and noticed you had your IOR on the table top material set to 3. Is there a reason for this? What sort of material are you trying to create for it? A reflective plastic would have an IOR of around 1.4

The combination of the higher than usual IOR and diffuse make it look like it is receiving more light than it is. But the reflection pass shows the object is not reflecting brighter than the light it receives. Just the added diffuse makes it appear visually brighter.

Richard

[wizlon]

Thanks for taking a look Richard. IOR was pushed up a little to emphasis the effect, but something still doesn't feel quite true. The reflections still look a little odd, especially on the top box left hand side of the first image I posted. I'm happy to be wrong here and hope that VRay is actually producing physically correct results. Arnold gives the same result.

Can you achieve the look from the photograph in render? - I can't seem to match it.

Regards,

Lee.

[chuckie7413]

Hi Lee.

Did you take the photograph? How do you know that photograph has not been manipulated to make the reflections of the boxes darker?

Best,

Richard

[wizlon]

I didn't take that photograph, but I have taken similar and had similar results as shown. I will try and do a reference shoot and post some more examples.

Thanks.

[Algehov]

I havnt checked your file yet, but it looks right when im recreating the scenario in your photo.

I have attached my scene so you can have a look.

[wizlon]

Perfect! thanks. I'll check your scene and compare against mine and see what the main differences are.