Environment Fog only as RE?

[dlparisi]

Is it possible to have the VrayEnvironmentFog only render as a render element and not part of the beauty pass? The short tutorial here (http://www.the-boundary.com/blog/201...-08-atmosphere) mentions it but I can't find a way to enable it to only be a render element.

[Zdravko.Keremidchiev]

You can't have VRayEnvironmentFog affecting only the Atmospheric render element. Instead you can set an additional render with override black material, Environment Fog and Atmospheric RE. Then you can comp the resulted render element with the original RGB image in post.

[dlparisi]

Yeah, kind of what I thought. Just trying to avoid the additional render if possible. Thanks.

[vlado]

You can always subtract the Atmospherics render element from your RGB image, and you will get the result without the fog.

Best regards,
Vlado

[dlparisi]

Yes, that's an excellent way to do it. Only caveat is that it only works when working linearly (32 bit photoshop, etc). Similarly, adding it back in in Photoshop in anything but 32 bit PS gives a different result than the straight render. Regardless, it should let me isolate areas that I don't want to have any fog. Thanks!

[dlparisi]

Sorry to bring back this old thread but it seems like Vlado's solution doesn't work any more (I can't recall if it ever really worked in practice). The VrayEnvironmentFog seems to darken the rgb image in areas that aren't illuminated by the light (at least in Vray 6). If you then try and subtract the VrayEnvFog RE it doesn't affect these darkened areas so you're left with a darker scene. Am I missing something or has something changed? I'm still trying to avoid having to setup another scene and separate render.

[hermit.crab]

Sorry to bring back this old thread but it seems like Vlado's solution doesn't work any more (I can't recall if it ever really worked in practice). The VrayEnvironmentFog seems to darken the rgb image in areas that aren't illuminated by the light (at least in Vray 6). If you then try and subtract the VrayEnvFog RE it doesn't affect these darkened areas so you're left with a darker scene. Am I missing something or has something changed? I'm still trying to avoid having to setup another scene and separate render.

If you are comparing a non-fog render with a fog one that has the fog extracted, I don't think they should match. When an atmosphere is present, the overall lighting should be affected by it, making the scene a bit darker, even if you remove the fog. This is not the same as not having an atmosphere at all.

[dlparisi]

Yeah, that's basically the issue I have. I was hoping to be able to easily get back to a non-fog render without a re-render whenever fog is enabled so I would be able to then add the RE in post. I guess I want the scene to not darken wherever the fog is not illuminated by a light. I realize this is very non-physical but was hoping for a workaround.

[dlparisi]

I have a pretty janky workaround of setting the EnvFog parameters really far (like a mile or two for the distance). You can then do a back to beauty composite render and then adjust the multiplier on the Vray Atmosphere layer to boost the volume light, or boost the multiplier in the RE parameters in the Render Setup dialog (or both really). It works to allow adjusting the affect AFTER a render, or remove it altogether if necessary. Not perfect but it'll do in a pinch.