Vray MultiMatte as Adjustment Layer

[Crazy Homeless Guy]

I have a Vray MultiMatte Render Element. Currently that pass is using only the red channel. I want to use this channel as an adjustment mask in AfterEffects, but I am not sure how. I can only figure out how to use adjustment passes with Alpha Channels, and individual color channels.

 

Any ideas….???

 

I could run a Photoshop script that copies the red channel to the alpha channel to fix the problem, but this is a patch, and I tend to use MultiMattes a lot so it would be best to figure a direct workflow.

[cgrant3d]

Just apply a "set channels" effect to your multimatte and set its alpha channel to be the red channel. Now set your adjustment layer to use the multimatte as a track matte or an alternative workflow (that can look cleaner in your comp) is to use the "set matte" effect on the multimatte which will allow you to put your multimatte at the bottom of your comp, out of the way instead of above it like a trackmatte...

[Crazy Homeless Guy]

Thanks. After some finessing with it, that worked.

 

...out of curiosity, what would be a method for a cleaner workflow? I always considered Vray MultiMattes to be very precise way to adjust elements in a scene in post. I typically do this in Photoshop and not Aftereffects.

 

Is it just the matter in which I am applying them in Aftereffects?

[cgrant3d]

I'm not sure what you mean about your After Effects multimatte's not being clean. I'm guessing you're getting a fringe around the edge? If so there are tools in AE to deal with this. First off though - are you using EXR files and are they coming into AE linear or gamma adjusted? If they're coming in linear then you'll need to apply an exposure effect to the multimatte to avoid fringing...

 

Alternatively - if you're doing everything right and you're still getting a fringe around the edge then I suggest exploring the matte choker effects. I've put together an AE file that shows what happens with correct / incorrect gamma and applied a matte choker so you can turn it on/off to see what it's doing.

 

Here's the AE file and source EXR's

http://www.christophergrant.com/files/multimatte%20demo.zip

[Crazy Homeless Guy]

I am not having fringing this time. I was simply responding to this... "(that can look cleaner in your comp)." I wasn't sure if you were impying that my workflow was badon this.

 

I am in 16bit EXR right now, and was simply using the MultiMatte to do a level/screen adjust on a stair tower that was not quite popping enough.

 

I will look at the attached file.

 

Thanks for the help.

[cgrant3d]

Oh haha... Totally misunderstood you.

 

The reference to having a "cleaner" comp was just that IMHO using trackmatte's seems to be the "AE way" but it feels cluttered to me.

 

Using a trackmatte workflow you'll have a comp that looks like this:

 

TrackMatte 1

Adjustment Layer 1

TrackMatte 2

Adjustment Layer 2

TrackMatte 3

Adjustment Layer 3

Base render

 

If you use a "set matte" effect instead of trackmattes you can arrange your comp however you like because the effect will let you specify where to get your matte from (as opposed to the layer above). So this comp could look like:

 

Adjustment Layer 1

Adjustment Layer 2

Adjustment Layer 3

Base Render

Multimatte1

Multimatte2

Multimatte3

 

Trackmattes are a bit easier to work with IMHO but sometimes the way they break up the visual flow of my comp really bothers me. Which is why I've really grown to like Composite! Once an AE comp gets very large (multiple color corrections, layers of additional rendered objects) it gets harder to work with but the node based workflow in Composite really starts to shine.