Shadow Catcher plus Lighting

[White Wizard]

How would i go about rendering direct light and shadows on a ground surface while also keeping the surface transparent, Alpha -1? basically a shadow catcher that includes direct light and GI as well? using vray next for 3dsmax.

I have a scene with police lights that light up the ground, to be comped over live action footage.

[hermit.crab]

Catching the shadows and GI may be done with a shadow catcher (through the object properties or a VRayMtlWrapper) with an Alpha of -1, yes. However, there isn't such a functionality to capture the light in a similar fashion. I guess you can create a basic environment resembling your footage and exclude the scene's lighting via LightSelects to overlay in post,

[JuhaHo]

Borrowing the topic a bit,

I wonder what would be the best way to increase light bounced from Shadow catcher V-Ray plane. My intention is to increase light that's send from ground upwards to illuminate more the downwards pointing surfaces - Brightness or GI-amount at V-Ray object properties?

[hermit.crab]

JuhaHo You can control the amount of the matte's generated GI through the "Generate GI" coefficient (V-Ray properties). If utilizing the matte functionality through the V-Ray properties, note that the generated Gi would be from the Background color (environment settings). If you wish to apply a custom GI color, you would need to use a VRayMtlWrapper for the matte plane, which is plugged into a VRayOverrideMtl with a separate shader for the GI color (see image).

[fixeighted]

They would show in reflections on the ground, so then matte for reflection would catch them. Might work.
Or if it's more complex than that maybe post an example frame and possibly we can think of another method if Aleksander's doesn't already solve it

[JuhaHo]

Thanks for Your answers,

I didn't get that override material. When I assign it to my V-Ray plane the shadow catcher effect disappear and there's no change on geometry itself. Maybe I did the material in a wrong way. Override material.zip

[JuhaHo]

I was too hasty, The shadows came back when I enabled the shadows in material wrapper.

After playing a bit, nothing seems to change the light when editing material. I even changed GI material to VRay light material with intensity of 1 000, but the was no noticeable changes in rendering. It seems only thing affecting the lightness is the scene background setting. I used grey constant color background. Changing it to pure white helped a bit. Then I enabled VRay sky background it helped a lot on dark area, but also increased the overall lightness of the scene so I need to iterate the main lights down to get correct color to renderings.

What would be the recommended options for VRay Sky?

[fixeighted]

Here is a small scene setup showing how it works
https://www.dropbox.com/s/hmm6xbgbrq...MATTE.max?dl=0

[JuhaHo]

Thanks,

It worked. I initially tried the material like Alexandar posted, but I saw in Your material there was additional wrapper on top and there I could adjust the GI-value in a way it affects my scene. When I got the iterations ready I still have one thing to improve.

Sometimes there's need to minimize the shadow footprint of the rendering. Using lights that generate small shadow footprint make the rendered objects look horrible. What would be the options for tightening the shadows on shadow catcher object. I use V-Ray plane as shadow catcher object, so it would be possible to use smaller objects, but the shadows might the look a bit silly.

[fixeighted]

You mean the GI spread on the floor? You can either lessen it in post but that's a hassle, or use different lighting that doesn't add to it as much.
An example would be good, to see what is happening. Maybe it's a case of using, for example, different lighting to create shadows only. Certainly more controllable.
On a slightly different note, that capsule example you attached....looks very like some recent hyperbaric chamber product renders I did....is this a similar project by coincidence?

[JuhaHo]

Actually, my tank primitive sample is not even near to my current project. However it served well for light iterations in this case. I did my studies with mechanical engineering and that's what I normally visualize/animate, but this project is something else.

After few iterations with lightning I wasn't able to find a way for minimizing the ground shadow footprint.

[fixeighted]

Ah ok...this is what I meant https://henshawhyperbarics.co.uk/hyp.../henshaw-solo/
Would have been spookily coincidental

Anyway, if you can simply block out what you're visualising, then I will see what setup I can devise for it

[JuhaHo]

I'm still having one issue with my ground shadow catcher object. I wonder what would be the best practice for minimizing the ground shadow footprint. Sometimes when doing a product visualization, customer wants to have very tight ground shadows below the object. When rendering with dome light with HDR sphere mapping, the ground shadow cover quite large areas.

[fixeighted]

There was a post a few days ago asking a similar question. I did it with a distance texture here...the lighting's crap I know, so ignore that.
The floor isn't being lit.
I copied and reversed the distance tex into opacity if an alpha was necessary. May work for what you need.

[JuhaHo]

Thanks,

I didn't quite get how it's working. Is there a flow sheet of that material available?

I still want to stick in my main scene light setup with the ground shadow catcher too. If I would use tight directional light for shadows only just above the product to be visualized, I might get tight shadow as desired, but then I would loose the height due to lack of horizontal light. I'm looking a way to keep the ground shadow near the product in a way that the shadow is not cut by image limits.