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Shadow Matte: Indirect Specular not showing reflections with black value?

Message 1 of 9
1949 Views, 8 Replies

Shadow Matte: Indirect Specular not showing reflections with black value?

I am trying to create a VFX compositing workflow, but am hitting a wall with the Shadow Matte shader. Pretty sure I'm having some fundamental misunderstanding here..

I can't figure out a way to generate accurate reflections through the Indirect Specular settings. When the scene's background image is visible, only the highlights are reflecting on the floor and not the dark values, creating a glowy/additive look. Dark objects totally disappear.

My set-up is simple: a floor (with shadow matte), a few primitives sitting on top, a light source, and a background object. The Shadow Matte is mostly default, with Indirect Specular Intensity set to 1, and IOR set to 0.


Look at where the objects touch the floor - the black cylinder disappears completely, the red sphere is practically glowing, and the green sphere's reflection doesn't have any of the shadowing from the underneath part.


With the background disabled, you can see how the problem goes away. Which to me implies that the shadow matte is getting blended in an additive way on top of the background image, completely cutting out all black values.


Here's my bad photoshop attempt to show what it should look like (or at least close to it, realistically the reflections wouldn't be that sharp)

Can someone explain what i'm missing? Is the solution to export everything as AOVs and composite them in AE/Nuke? I'm really trying to avoid that and get everything looking right in the viewport. Please help, thanks!

Here's the project file:

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Message 2 of 9
in reply to: chrisjbh3

Still stuck, bumping for visibility

Message 3 of 9
in reply to: chrisjbh3

So after some research, I've found that reflections rendered as passes indeed are captured as highlights with the expectation that they will..., effectively cutting out all black values.

This is surprising, considering Arnold is used quite a bit in VFX and visual compositing work. There must be a solution, right? In this video, this artist clearly was able to render out a dark reflection of the spaceship on the street. I even subscribed to Digital Tutors just to watch this tutorial, but since I don't use Nuke I wasn't able to get a lot of meaningful info from it.

Message 4 of 9

Our shadow matte shader is a basic one and it does only additive blending as you noticed. We are planing to improve it in the future and address these more complex cases, but I have no ETA at the moment.

Message 5 of 9
in reply to: chrisjbh3

I'm also having problems with the shadow matte, I can not reflect the shadows of one object in another without you see the ground (image plane)

Message 6 of 9
in reply to: chrisjbh3

Any solution or workarounds to this?

Message 7 of 9
in reply to: chrisjbh3

This is really a shame...

I'd render a regular ground pass, and try to mask out the reflection somehow...

Arnold shadow catcher:


Arnold regular material:


A quick test shows its in Redshift as well.

Redshift shadow catcher:


Message 8 of 9
in reply to: itaibachar2012

Exactly, create some AOVs that does the job for you and composit at free will till it looks like you want.

Message 9 of 9
in reply to: chrisjbh3

I've found a work around. Giving the reflected object an emissive white texture and using that specular pass to mask the original reflection in nuke.

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