How to deal with refractions and background in comp?

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Om Gothi asked · May 20, 2019 at 05:06 PM

How to deal with refractions and background in comp?

Hello everybody,

I wanna know what is the best way to deal with refractions in comp preferably nuke.i want to know how to adjust the background in nuke without affecting the refractions. I watched arvid's video on this:https://youtu.be/PUJZQKXW67I .But it isn't clear to me on what to do if i dont have geometry or projections. What to do when you have just a image plane? What to do if you haven't decided the backplate yet or it has to change? i dont think that the refractions affect the alpha channel. How to deal with this. Any help would be really appreciated.Thanks in advance.

@Stephen Blair @Lee Griggs @Zeno Pelgrims

mtoa light aov material

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Answer 1 · 2019-05-26T11:43:24Z

Om Gothi answered · May 26, 2019 at 11:43 AM

No I will try

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Answer 2 · 2019-05-24T10:39:45Z

Lee Griggs answered · May 24, 2019 at 10:39 AM

Did you try Transmit AOVs?

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Answer 3 · 2019-05-24T10:21:12Z

Om Gothi answered · May 24, 2019 at 10:21 AM

@Ashley Handscomb Retallack

I think that is a terrible idea.Also the whole meaning of comp is to not to re-render every time you make a change.

@Lee Griggs

I want a very simple thing.i just want transparency in my alpha channel in all aovs and beauty. like in redshift when rendering refractions.

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Answer 4 · 2019-05-21T07:23:54Z

Lee Griggs answered · May 21, 2019 at 07:23 AM

You are using Transmit AOVs?

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Answer 5 · 2019-05-21T06:40:33Z

Jose Miguel answered · May 21, 2019 at 06:40 AM

I don't know your compositing package, but, for Nuke, you have gizmos to deform an image based on the AOVs created for that specific task, and it looks great, trust me.

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Answer 6 · 2019-05-20T20:15:48Z

Ashley Handscomb Retallack answered · May 20, 2019 at 08:15 PM

Unfortunately, the best way is to re-render the refractions, you can render them as a separate AOV for compositing back, which will speed up the process a lot.

But no comp trick will be as good as real raytraced refractions, especially if there is any roughness in the transmission.

Arvid's method is to get the UV (ST) coords from the refracting geometry and using that to drive the distortion. This works for geometry when it hasn't got anything else behind it, but as soon as you have the geometry and the background you wish to distort it can get pretty complex.

If you have an example scene of your setup we can take a look for you.

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