Enabling Volumetric Environment negatively effects Material Random Color Pass

[ds73]

Enabling volumetric environment in a scene makes the material random color pass more or less unusable for compositing/post work in photoshop by effectively gradating the color of the material in the random color pass. Here is a simple scenario with just two generic materials, one for the surround and one for the boxes arrayed away from the camera. With no environment the materials display as defined single colors, but with the environment enabled they are displayed as gradated tones. Is there a way to tell vray to ignore atmosphere in the material pass?

thx

[slavcho.brusev]

Hello

Seems I can’t reproduce this on my side.
I am testing Environment fog with Material_ID_Color render element.
Could you please share an example to check in our environment?
You can attach it in the request below, please just include a link to this forum post for reference.
https://support.chaos.com/hc/en-us/requests/new

[ds73]

File sent. Thanks for taking a look.

d

[slavcho.brusev]

Hi,

Seems like this is a limitation of the Environment Fog.
2 possible workarounds in this case.

1. Use the ZDepth render element (basically adding fog in the post)- this will create a render element that displays the distance from an object to the camera with a grayscale image. Please see the link below for additional information
https://docs.chaos.com/display/VRHINO/ZDepth
The benefits of using this over the Environment Fog are faster render times, easier compositing(the fog will be separated from other render elements), and repurposing the same render element as a focus mask.

2. Use masks without antialiasing like Material ID number, Object ID, Render ID, or MiltiMatte Materials/Objects in non AA mode

[konstantin_chaos]

Hi ds73 ,

The fact that the volumetric environment alters the mask elements has been a known limitation in V-Ray for a long time.
It is unfortunately something quite hard to address.

The bottom line is that V-Ray does not evaluate the render element passes separately.
It does it in a single pass, in a really optimized way, without increasing render times.
The rays used for producing the beauty render are the same ones that feed information in the separate channels.
In your case the Fog filters all rays traveling through it (making them dimmer) and when the rays reach the object the same filter is applied to the mask.

We will revisit this topic in the future and hopefully find an elegant solution.

Regards,
Konstantin