CC Glass bump map issue when applied footage instead of composition

Question

I've followed a neat tutorial on making a rain drop on a surface. It uses bunch of Turbulent Displacements and Particle effects to create a black and white bump map.

That map is fed into CC Glass to create refraction. I wanted to render just the black and white bump map to avoid overhead with Turbulent Displacements etc...

My problem is, that when I use a video or image sequence of a bump map, cc glass renders completely different than if I use the actual composition, created at runtime.

Check this images:

With prerender as bump map: http://imgur.com/a/WrEx9

With composition as bump map: http://imgur.com/a/gjwzj

http://imgur.com/a/Nmu4b

To further prove my point, check this image of a bump map composition and bump map .mov prerender. There is 0 visual difference. And even if there are small differences, that shouldn't cause so many artifacts.

At first it looked to me that there is a lot of pixelation going on. But on further inspection I realized that center of all lines doesn't even have a refraction. Like it is cut of.

I've repeated this with openEXR image sequence and the issue remains.

Moreover, this result is different as if I choose 8 bpc color settings. If I do that all of the bump map is completely pixelated, but in my case with the prerender, only edges are maybe somewhat pixelated so that probably isn't the case.

You can download project files here: VIDEO COPILOT | After Effects Tutorials, Plug-ins and Stock Footage for Post Production Professionals

Can someone explain why is this happening? I'd love if someone can reconstruct the problem to cross me being stupid of the list.

Thanks, cheers

Jose Panadero · Accepted Answer

Hi TimSx. In your project, you have to understand the AE's render pipeline. As I have suspected, you have applied a Levels effect to your Water Texture precomp. After Effects, uses the original layer as it is: a comp without effects. If you want the effects to be part of your composition you have 2 option:

1.- To precomp again transferring the effects to the new comp. Then CC Glass will look exactly the same using any of the sources.

2.- Use the new option in the latest release that allows you to refer to other layers including their masks and applied effects. This can be done in CC2017 v14.2. If you are not using the latest version, the only way to do it is step 1.

Look at the attached image to understand what I'm trying to say.

Hope this helps

TimSx · Answer

Hey Jose! Thanks for taking your time. You've been a life saver. Basically you are saying that when Water precomp is used as a bump map, levels are not taken into account at the time of making a bump map, but are applied after? That is because effects are added from bottom layer to top one, and because when glass effect is added, there is no levels at the precomp.

Second thing, I didn't really catch what needs to be precomped again to transfer effects.

I rendered Water_texture composition without the levels effect, replaced Water_texture comp with the render and applied levels afterwards. That worked, but only if I used exr and 32 bit project, otherwise it seems that a lot of data is being lost and everyting is pixelated.

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