MultiPass Shadows Problem

[BigAl3D]

In the image below, I will be replacing the blue material with a video or static image in AE on the left image. As you can see, will need to have a shadow pass so I can composite those shadows back over my new screen images. The resulting shadow pass (right image) has me very confused and I can't seem to find anything online more that "here are the multipass options" and how to enable them. I was expecting more of a grayscale version of my scene so I can Multiply it over the RGB image. What am I missing here?

[TomG]

This is what the Shadows pass does:

"Shows the shadows (energy subtracted from the image due to shadow ray occlusion). This is the complement to the beauty pass, showing white where there are black shadows. If this pass is linearly added to the beauty pass, it negates the visible shadows. Note that currently the shadows from environment lighting are always shown, resulting in a washed-out pass in typical interior renders."

See https://help.c4d.corona-renderer.com/support/solutions/articles/12000023596-what-multi-pass-channels-are-available-

[BigAl3D]

Thank you for the reply Tom, but I have read that as well, and I don't understand it. How can I USE this pass in After Effects to add shadows back to my comp? I've tried many combinations with odd results at best.

Now, I have some success after dropping a Shadow Catcher material onto the screen. I brought that into AE and added an Invert effect, but this just turned the image completely white and even after turning on Multiply for the layer, it had no effect. I was able to darken it a lot and only then was I able to see any shadows. It will work, but there has to be a better way.

For example, I set up an AO pass as well and it produced a perfect grayscale image to multiply only my scene. Done in 5 min.

[TomG]

Might be good to share the layers you are using, plus exactly what you are trying to achieve. Since the Shadows pass is there to remove shadows from the Beauty pass, inverting it should give you something to add to a pass with no shadows. Never personally explored it though, and users may well be able to advise depending on what it is you are looking to do - e.g. enhance shadows in an existing beauty pass by making them darker? Add them only to certain places in a render via masks? Add them to a composite of various layers that you need which don't happen to have shadows already?

Cheers!

[BigAl3D]

OK so after seeing another thread about removing objects and shadows to be used separately, I forgot that I never posted my process which pertains to this post. So for me, and I imagine other motion designers, it's not about removing shadows from the background, but adding the shadows back in because content has been replaced. Or simply having more control of the shadows to avoid re-rendering the 3D scene.

In this image, you can see ultimately, the screen can have many different types of content done in After Effects. My solution was to add the Shadow Catcher material to the screen object. This gave me a more traditional result of just shadows, except you need to Invert the result so you have dark shadows. Now it can be placed on top of the screen and it's mode set to Multiply. AO is also Multiplied, but that pass renders as I would expect so nothing needs to be done to it's output.

The final result is here. Not perfect, but pretty good results. Still some dancing edges here and there.

https://vimeo.com/tier10studios/review/319494015/081cb91c9f