Background exposure problem

[DCHA34]

I know that it is possible to set a custom background in VRay in Environment/Screen mode.
But is it possible to make it unaffected by the exposure?
Searching the forum, this does not seem to have been implemented in either 3DSMAX or Vantage.
Can you confirm that this is not possible in Sketchup?

Don't you think it would be nice to have this option?

[tsvetomira.girginova]

Dear DCHA34, hello.

If we compare to Screen mode - this could be done in VFB2 by adding Background & Exposure layers.
Load the image directly in Background layer, additional adjustments are also possible.
Just be sure that Background will be above the Exposure one in the Layer tree.


Best regards,
TS

[DCHA34]

Hi,
I know this option.
I did not express my request well. I am trying to make a photomontage with shadow catcher on a 2D image (backplate) taken with a camera.

With the method you describe (background image in VFB), I did not manage to get the desired effect, despite my various attempts in Composite mode. But maybe I'm doing something wrong.

I found this tutorial https://www.youtube.com/watch?v=FfwO5nHqL0I for 3DSMAX, but I couldn't reproduce the effect in V-Ray for Sketchup.

Again, maybe I'm doing something wrong.

[tsvetomira.girginova]

Hello,

now this leads the discussion in a totally new direction. So, thank you for sharing the example!
And excuse us for the delayed response.

In your initial post you mentioned that it is not implemented in 3dsMax, but the whole video example is recorded within 3dsMax with V-Ray.
I understand that your wanting is to receive this result easier than now and to have well working alternative in SketchUp with V-Ray.
Every host platform has its own dis- and advantages and not every time everything could be translated exactly.
But let's try together. We will appreciate to share the exact point that you have reached while trying to replicate this in SketchUp.

1. Download a Backplate
2. Set the render resolution to be equal to the Blackplate one
3. Load the image as a Background
4. Use Perspective Match (3dsMax native option) <> SketchUp alternative is Match Photo
5. Align what is needed to match the camera angle
6. Render and see that the Backplate isn't visible in both platforms which is normal since it is added only to the viewport
7. Plan A: Use it in a Background Layer in VFB2. Here I won't agree about the transparency objects, they are working fine. Zooming is good too.
Lens Effects could be added above the Background Layer, check p.15.
8. Plan B: Add it to the Environment in Screen mode. Maybe here you have met the issue about exposure.
9. Overwriting GI, Reflection, Refraction, Secondary Matte is possible in both platforms. As you know in SketchUp it is: V-Ray Asset Editor > Settings > Environment.
10. Recreating Lights and GI may be more challenging compared to 3dsMax, because the control over the SunLight in SketchUp is different. The V-Ray sun is tied to the SketchUp shadows and sun.
11. Creating a ground geo and defining it as a Matte is also possible by using Wrapper material
12. Trace reflections, Affect Specular (SunLight) are available options...
13. Color space option for VFB Background will be revealed, it is in progress now as an improvement.
14. MultiMatte is applicable within V-Ray for SketchUp too. You could choose between MultiMatte Materials & MultiMatte Objects.
A little detail is how you define them - for Materials additional Material ID Attribute should be added and defined, for objects - by right-clicking over the chosen object go to V-Ray Object ID.
15. Final adjustments in V-Ray Frame Buffer. If you use Source: Composite (the third option next to RGB and LightMix) you could add Lend Effects above Background and also perform many more postproduction work at one place.


Workflow is showing a personal style. The Author here is using the Backplate for setting the view and having an exact background look (collage-like). Lighting is independent from it.
So, in general this leads to Background Layer in VFB.
Since one of the pluses of a Backplate is the exact view, which was hard to achieve before with a HDRI, now - with Finite Dome you have more control over the placing and the final appearance.

If you share the exact step when you are at, perhaps we could be more helpful and discuss it straight to the point.
Please keep this in mind.

Wishing you a wonderful week,
TS

[DCHA34]

Thank you for answering so precisely.
I think I'll keep the VFB Background solution.
The "Add it to the Environment in Screen mode" solution is unmanageable for me.
"Maybe here you have met the issue about exposure." That's exactly it.

Thanks again.

[tsvetomira.girginova]

You are welcome.

If we are talking about additional Exposure Layer, it could be added only for certain masks (right-click over Exposure > New Layer and choose the wanted mask) and limit the postproduction effect to certain objects/materials.
Then you could use also the slots in Settings > Environment for the Overrides and for Environment Texture.

But the whole idea is closer to the initially recommended way.
Test all possibilities and choose the best for you.

Indeed, interesting topic, thank you for it.

[RobH22]

This post was very helpful to me on a project I'm doing. Thanks for all of the posts sorting it out.

[kenancakir]

I use background images in screen mode with Sketchup photo match. To avoid over exposure i decrease the background value and it works fine. Of course i use gi section under background to add hdri or sky for lightning, or dome light with invisible option on..

[konstantin_chaos]

I use background images in screen mode with Sketchup photo match. To avoid over exposure i decrease the background value and it works fine. Of course i use gi section under background to add hdri or sky for lightning, or dome light with invisible option on..

This is the correct approach.
As soon as the Screen background is added, you should ensure to override all the other environments - Reflection ,Refraction, GI, etc.
Then you'll have the ability to alter the exposure of the background independently.