correct workflow for comping in mattes with shadows.

[thomas_bussey]

Can anyone tell which REs I need to correctly comp shadows in from a matte? I know all about linear workflow, back to beauty etc, but I'mm pretty sure my previous attempts have been wrong (just multiplying the alpha with the existing backplate)

Thanks.

[Joelaff]

Separate the shadow completely and then use it as a mask for a color correction that makes a shadow that matches shadows in your scene.

[thomas_bussey]

. Double post

[thomas_bussey]

That doesn't seem like it'll be physically correct. It relies on user judgment. Surely it's something that's just possible with math?

[Joelaff]

Ha! Well, that’s how it’s done in VFX industry. All that matters is how it looks. If you are comping into a BG plate you aren’t going to get any better than that. Multiplying your shadow won’t let you do things like make the highlights darker than the shadows in the BG plate under the shadow.

That’s why it is VFX Artist rather than VFX Scientist. It surely requires a little bit of both, but a good eye is far more important than the technical stuff.

Perhaps I misunderstood and you want the shadows comped into a purely 3d scene that you have rendered, rather than into a live action backplate? That can be done with math.

Of course if you are setting that up to adjust in post then you are getting into that art thing again, since adjusting it in post is not the math approach, which would be to light it the way you want it in the scene, and let the renderer handle the math.

In the end whatever approach looks good is best. I’m not going to say I have never multiplied a shadow onto a backplate, but it usually takes more finesse than that, much to my chagrin.

[Joelaff]

Duplicate post. Silly forum…

[piotrus3333]

technically it’s a subtraction. in practice, like mentioned above, just a mask.

[thomas_bussey]

Yes actually I should have mentioned that. The backplate and matte come from the same scene. I just want to split them for... reasons... In this case to try some additional post processing on the matte that may change it's shape a little, but it could also be useful in other scenarios.

So piotrus3333, subtract a VrayShadowsRE from the RGB beauty pass and it should be correct? Now you say it I feel like I already knew this

[thomas_bussey]

Oh wait, I can't use Shadows RE because my shadows should be coming from the matte renders.

I Was thinking of using the material override/wrapper method but then again maybe if I use the the Vray properties method I could actually get a proper colored VrayShadows element.

I'm so confused. Of course I could just experiment until I find a method that works, but I figure this must have an 'official' methodology.

[piotrus3333]

So if you have the whole scene together - maybe just render the plate with all the shadows?