How to use an Environment Background that isn't affected by the camera exposure?

[bob dobbs]

Heya!

I'm doing a bunch of CG against footage, I'd like to use IPR / Progressive to scrub my animation against the background. But the environment background is affected by the camera exposure, so any adjustments that I make mess with footage brightness. I found a few posts that address this, but it looks like it is not possible to use Progressive rendering in this way. Is that true?

[olika]

Hi Bob,
did not tried to reproduce it by myself but does the "affect background" checkbox under colormapping rollout something about this issue?

[bob dobbs]

No, unfortunately. Neither the option "Process Background and Environment Maps" in the Environment Dialog, nor the "Affect Background" option in the VRay color mapping rollout prevent VRay from messing with the environment background when using progressive rendering. Bucket is fine, but for fine-tuning colors it is clunky. Problem is that Progressive would be perfect when match-moving and matching colors in a shot. But I can't see any other way except for loading 1 image at a time through the VFB

[fixeighted]

How odd. Maybe just currently unsupported but definitely problematic unless we're missing a check-box somewhere - I just spent a half hour looking but don't see anything.
Where are the other threads you mentioned?

[Margarita.Stoeva]

Hello!

The proper way to skip exposure on Environment background is indeed to disable the Affect Background option in the Color mapping section of Render Setup V-Ray tab. This option still doesn't work with Progressive image sampler and I'll bring this issue up in our bug tracking system (it's logged under VMAX-4902).
Your options are to either use bucket sampler (this is available in IPR when you disable Force progressive sampling option in the IPR options section of Render Setup V-Ray tab) or if you need progressive image sampler you can eventually assign the footage to be used in a VRayLightMtl on appropriate geometry (use it instead of background), and enable the Compensate camera exposure option of the material.
Write back how this went so we can help further if needed.

Best regards,
Margarita

[fixeighted]

Yeah that's a reasonable enough workaround (using a cam-linked plane for the tex).
Thanks.

[bob dobbs]

...if you need progressive image sampler you can eventually assign the footage to be used in a VRayLightMtl on appropriate geometry (use it instead of background), and enable the Compensate camera exposure option of the material.

Thank you! That is very helpful. This does solve the problem, now I can scrub the time slider and fairly quickly get a good idea of how well the geometry integrates with the color and the placement!

This creates new problems. My shadow catching objects with alpha set to -1 cut out the backplate geo right where I need it the most.

Anyways, thank you for your suggestion, it does solve part of the puzzle.

[JD3D_CGI]

I know this is a blast from the past - but I seem to be having the same trouble in a much later version of Vray - the option to ignore the background in exposure control is broken.

[hermit.crab]

I know this is a blast from the past - but I seem to be having the same trouble in a much later version of Vray - the option to ignore the background in exposure control is broken.

Do you mean the "Proces Background and Environment maps" option? Use the "Affect Background" option (Bucket only) in the Color Mapping settings instead.