Scatter grass too dark in some cases

[Witt3D]

Hi, we are always struggeling with this same issue.
We tend to correct it on post, but we dont know if we are doing something wrong or not.

First preview scatter grass is too dark, second preview shows up our simple grass material (Two side material), and third preview, same camera, same light system and grass comes out in a perfect way, just sun from HDRI is hitting straight.

We use to think, that we can setup up a good material, and as vray is "physical correct", onces is really good setup up, this material should work out in every single condition.
Perhaps we are setting up the grass material in a worng way, but grass doesnt handle in that way under this light conditions.

Some light to this issue would be really helpful.
Thank you.

[intercard]

Hello Witt3D

Maybe i will need more info and the team Chaos too about your scene and materials !!!

But while they answer you, I leave you a tutorial of mine for VRay Next on how to create a vegetation material are in Spanish Audio but i made the subtitles into english for help to all:

Go to time 17:05

Here the Link: https://youtu.be/_VEHCH09LYk?t=1025

Soon I will do another tutorial to create VRay 5 vegetation materials for Maya using Thin Walled + the new SSS of the VRay Mtl and 2Sides Mtl.

[hermit.crab]

What's the difference between the two renderings? To me, it looks like the exterior of the darker is lit through a dim light (f.e. a twilight hdri map). Are the two versions using identical lighting conditions? If so, is it reproducible on a simple scene? Can you attach/send it for investigation?

[Witt3D]

Hi, light conditions are both the same, and camera parameters aswell. We got an hdri sky dome, and some interior lights. Darker grass is on a lower floor with some walls around. A part from that, the problem is that grass is not behaving it self like real world under that conditions. We don’t know if it’s a problem of our material, if vray handles narrow geometry and GI not as real world in that cases o what else. You can check with the floor. Is the same material in both renders. On the darker grass floor is still pretty bright, but grass drastically raise down brightness almost to pure dark. RGB (1,1,0)

[hermit.crab]

I would need to check the scene to give proper feedback. Send it as instructed above; mention me in the message and include a link to this thread.