GI bounces

[shapebubble]

Hi ya

I'm having trouble with my shadows.

I feel like I have a good material but I can't seem to recreate a real life scene accurately. I did a photo shoot a couple years ago so I can replicate the setting of the shoot in V-Ray and from what I gather that should reproduce a the same effect but that doesn't seem to be the case.

The real shoot had 3 photographic studio lights with full capacity of 800w each.
I had one light on full and the other on lower settings which means that the scene would have been at around 1000-1200w.
They were set no more than 2.5 meters away and no closer than 1 metre
The image of the real pot was iso200, f stop 4.5 and exposure 1/80

I think I have narrowed it down to the GI bounce being too high but I can't find out how to reduce that. The manual page (https://docs.chaosgroup.com/display/...ation+Settings) gives visual examples of varying bounces but no instruction on how to change the bounce amount. All I can see is primary and secondary.

I've attached the reference image from my real shoot and the scene pack is too large so it's here https://adamchristopherdesign.co.uk/...full-scale.zip

Thanks

[shapebubble]

I've done some comparison images with GI on and GI off if it helps.

As you can see the GI completely floods a nicely lit scene and destroys it.

Even without the lights on the scene is over whelmed with a mystery light.

[shapebubble]

Solved the flooding of light. Some how an environment image had found its way into the environment settings.

Still stuck on how to control how many bounces the GI can do though as per the images in the manual.

Thanks

[Micha]

Also important to know if you use a white color than it cause 100% reflected indirect light (GI). But at the real world the brightest white (snow?) reflect max 80% only. So, if you like to get less bounced GI light you need to keep bright colors below 80%, for example for white is needed max (210,210,210). In the past it was possible to limit the GI bounce by the secondary engine multiplier, I used it at 0.8 always, very day. So, no color correction to 80% for every material was needed. At VfR3/4 this very helpful option isn't available at the UI anymore, but still can be set it per editing the visopt file or using a button script like this:

! _-RunPythonScript (

import rhinoscriptsyntax as rs
vray = rs.GetPlugInObject("V-Ray for Rhino")
vray.SetSceneValue("/SettingsGI", "secondary_multiplier", 0.8)
)

I still hope the little option find back to the UI, maybe direct to the GI options.

georgi.georgiev What do you think? Is this option not essential to get a photo realistic look? It would be cumbersome to apply a multiplier of 0.8 to every color and every texture. Wouldn't be helpful for beginners and not so advanced users to use the factor 0.8 per default?

[Peter.Chaushev]

The recommended workflow is to use the optimized default values as set via the render settings quality presets and instead tweak the material parameters to ensure they do not appear too bright.
Interactive rendering is also hardcoded to BF/BF with 3 secondary bounces. While this value is adjustable, it is recommended to keep it as it is.
If you wish to adjust the GI a specific material contributes or receives, you can slot it within a Wrapper material and fine-tune its GI Affect values (https://docs.chaosgroup.com/display/...apper-GIAffect)

Kind regards,
Peter

[Micha]

The recommended workflow is to use the optimized default values as set via the render settings quality presets and instead tweak the material parameters to ensure they do not appear too bright.

Which is the parameter in the default settings that helps to avoid to get 100% GI light transport by white materials (255,255,255)? Or is the secondary engine multiplier set at something like 0.8 by default?

[Grigio18]

Which is the parameter in the default settings that helps to avoid to get 100% GI light transport by white materials (255,255,255)? Or is the secondary engine multiplier set at something like 0.8 by default?

simply I never use full white diffuse, it's been told us for years ... It makes a huge impact on gi,and render times aswell, I never go over 220 srgb ( a white wall is usually 200/205)
Other things I do are, using ggx brdf and activate glossy fresnel.

[Micha]

simply I never use full white diffuse, it's been told us for years ... It makes a huge impact on gi,and render times aswell, I never go over 220 srgb ( a white wall is usually 200/205)

That's right, I do it too, but if you start to keep white colors at real world level, than we would need to use a correction like this for all colors and textures at the scene, or we get wrong relations between the white (maybe the walls of an interior) and the objects in a scene. For example a simple painting with some strokes on this white wall would be uncorrected much brighter than the corrected wall. Or a textured news paper on a table.

Most difficult it is for design system colors for example like NCS. If my design client told me, for a train interior I need to use white NCS... for the wall, light grey NCS... for the seats, grey NCS... for the tables, red NCS ... for ... than I run in troubles, if would set the white of the walls to a grey (205,205,205) only. Than the wall would be like the seats. Do you see the problem?

[Peter.Chaushev]

There is no NCS swatch corresponding to color values of 255,255,255 or 0,0,0. As long as the V-Ray physical camera and light sources are set properly, it should be fine. Globally tuning down the GI is not an advisable approach.
Furthermore, for the purpose of troubleshooting there are options exposed in the Settings > Render Parameters > Color Mapping and Optimizations.

Kind regards,
Peter

[Micha]

For example NCS S 0300-N is in sRGB (246; 245; 242). This bright white would reflect ~95% of the indirect light and would cause a wrong light transport or?

https://www.e-paint.co.uk/Lab_values...Ref=S%200300-N

[Peter.Chaushev]

There should be no issue as long as the camera and lighting are properly set accordingly.