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Christopher James avatar image
Christopher James asked ·

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:

arnold-mattetest.zip

shadowmattes
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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)

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Itai Bachar avatar image
Itai Bachar answered ·

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:



001.jpg (101.9 KiB)
002.jpg (133.9 KiB)
rs001.jpg (136.2 KiB)
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Exactly, create some AOVs that does the job for you and composit at free will till it looks like you want.

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David Greco avatar image
David Greco answered ·

Any solution or workarounds to this?

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Peter Horvath avatar image
Peter Horvath answered ·

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.

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Christopher James avatar image
Christopher James answered ·

So after some research, I've found that reflections rendered as passes indeed are captured as highlights with the expectation that they will be 'added' to a comp later, 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.

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Christopher James avatar image
Christopher James answered ·

Still stuck, bumping for visibility

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