vrayvolumegrid "recieve gi" multiplier.

[super gnu]

playing around with clouds in the volume grid.. i notice that they do not seem to pick up much sky illumination.. with the sun on, they go quite yellow, and i have very little blue light tint from the sky. if i turn off the sun i can see they are recieving gi, but seems i have no way to control the ratio of direct/indirect illumination. the vrayproperties "recieve gi" multiplier has no effect.

i can make them much more visually pleasing by adding the vraysky to a domelight, and setting the multiplier to 1.5.. but that cranks up the rendertime.

[tashko.zashev]

Hi,
Just did a quick test and Receive GI worked fine here - V-Ray 3.30. Would it be possible to send me your scene ?

[super gnu]

here are examples:


A (rather ugly) cloud vdb.

constant colour set to very light grey.

with the default setup, (and daylight white balance) the lighting is dominated by the sun, and the cloud looks unnaturally yellow.

since i cannot control ratio of direct/indirect illumination (i dont think)

i add the sky to a domelight, and , in this case, set multiplier to 1.8

as you can see, it unarguably looks better. getting lots of nice skylighting, without blowing the sunlighting out noticeably.

now im sure there is some explanation as to why the first yellow one is more physically correct, but i want the second - without the 5x increase in rendertime caused by a domelight!

[super gnu]

we posted simultaneously... i have realised i was adjusting "send gi" doh.

having said that i can -still- get a much nicer result with the domelight, and im not sure why.


here is an example with "recieve gi" set to 1.8. -its still not getting that nice blue tint i get from the domelight.. why?






- i tried boosting "recieve gi" further, but it just blows out, no more blue tint..

[tashko.zashev]

Thank you for the quick update.
Can you send me that file so I can look at it? Max file plus VDB

[super gnu]

cloud.zip

here you go, its currently set to "recieve gi" 1, and the domelight is turned off.

[tashko.zashev]

Actually the only way to get bluish tint of the clouds is to adapt your lighting setup and find the best point at which the clouds lighting, shadows and ground lighting are good enough. Try to use the Sun light/s include/exclude lists to prepare a setup that allows you to control the clouds and other scene objects separately.
I have forwarded the scene to our developers so they will try to find a way to optimize the volumetric data sampling for scenes with V-Ray Dome light. Will keep you posted with any info.

[super gnu]

thanks for the feedback. i still dont understand why the domelight with sky in, gives a bluish tint, but the same sky as environment does not...?

[tashko.zashev]

thanks for the feedback. i still dont understand why the domelight with sky in, gives a bluish tint, but the same sky as environment does not...?

The difference comes from the V-Ray Sun light (color temperature) and its intensity. This lighting differs from the Dome light and this is somehow expected result.
Maybe you can adjust the Sun Filter color to get the desired effect in this scene?

[Svetlin.Nikolov]

Hey super gnu,

An additional thing related to the scene settings you can try is to increase the step size - I halved the render time with the dome light by increasing the step and shadow step sizes from 50% and 100% respectively to 90% and 400%. Since you don't have fire which usually requires a specific intensity curve, and you are using simple smoke opacity, anything below 90-100% will have a negligible effect on detail. Increasing shadow step size will significantly reduce the render time, especially for dome lights. It will brighten up the shadows a bit, which is an effect I have to investigate.