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"Light" leak from glow effect on supposedly masked object

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Liz McLean Knight
"Light" leak from glow effect on supposedly masked object
on Aug 18, 2018 at 9:07:53 pm



I'm a bit new at After Effects so I'm probably getting the render / layer / mask order wrong or something. I wanted to remove the Chromatic Glow effect from the red bag, which I was able to do. However, the Chromatic Glow is still being applied to the red bag and showing the glow effect on the un-masked bit at the left.

So what's the best way to get rid of the Glow from the bag but leave the Glow emanating from the Faerie?

Thanks!


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Steve Bentley
Re: "Light" leak from glow effect on supposedly masked object
on Aug 18, 2018 at 10:46:12 pm

The adjustment layer is applying the glow to every thing so even though you are masking the bag, the glow is looking at all pixels to determine the colors and the mask is just being applied to the adjustment layer not the effect itself.
I don't have ChromGlow but perhaps there is a "use mask or use mask and effects" settings that may combined the mask into the effect. Another option may be "premultiply" in the effect's settings that might do the trick.
A better approach to the shot would be to do a rough mask around the fairy layer, with a feather so you don't have to be too accurate, and then place the that layer over an original of the shot and tell the effect to show the effect only. Then you can have the glow bloom over the back but not glow the back itself.

Even better might be to mask the fairy and then precompose her on a black solid. Then put the glow on the precomp layer in your outer comp. The precomp would sit over the original shot.

You may need a different blend mode with the Chrom glow in this method (screen or perhaps overlay)



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Andrew Somers
Re: "Light" leak from glow effect on supposedly masked object
on Aug 19, 2018 at 3:19:58 am

Masks don't respect what an effect on the same layer "sees", only what that layer outputs.

As such, you need to:

1) Remove that mask from the adjustment layer.

2) Apply that mask to the footage layer below to cut out the bag entirely.

3) Copy that footage layer and put it ABOVE the Adjustment layer.

4) On the copy above, change the mask to ADD instead of subtract (or make it not inverted — also remove from the above layer any masks that conflict with showing the bag clean.)

5) if needed, expand and feather the mask on the above footage layer to smooth the edge.


Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Liz McLean Knight
Re: "Light" leak from glow effect on supposedly masked object
on Aug 26, 2018 at 7:58:48 am
Last Edited By Liz McLean Knight on Aug 26, 2018 at 8:15:28 am

Hi, Andrew,

I think I got it from following your instructions!



There is some weird shadowing going on between the two copies of footage... will play with it tomorrow.

Thanks!

http://subvariant.com


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Andrew Somers
Re: "Light" leak from glow effect on supposedly masked object
on Aug 26, 2018 at 9:04:28 am

Hi Liz, the shadow is now caused by the hole in the fairy footage - as I recall the glow effect was an adjustment layer, which is now below the bag and above the fairy?

The quick fix: Just put a SOLID layer right below the fairy footage with the hole, and set the color of the solid to be close to the fairy's dress. It won't be seen as its covered by the bag, but it will feed the effect on the adjustment layer.

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Liz McLean Knight
Re: "Light" leak from glow effect on supposedly masked object
on Aug 31, 2018 at 11:24:14 pm

I put the effect directly on the footage layer "fairie no bag" instead of the adjustment layer. I turned off the feathering on the "floating bag no glow" and the shadow went away, however now there is a distinct line around the mask.



In another thread they said to set the blending mode on the top layer to Alpha Add. When I do that it lightens the line slightly, but it's still there:



I tried putting a layer underneath "farie no bag" in a light blue color, but the line is still there, albeit colored light blue now.



Any thoughts on what's causing this?

http://subvariant.com


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Andrew Somers
Re: "Light" leak from glow effect on supposedly masked object
on Sep 2, 2018 at 12:30:31 am

Hi Liz,

Yes dealing with matte lines is the never ending task for compositors.

I see you're in 8 bit mode - 32 bit float might help here, but also are your bag and BG footage masks the exact same size? It might be better to overlap them by expanding one of them, and then feathering them both.

Although that effect you're using might only be 8 or 16 bit, working in 32 bit with color space set to linear makes these kinds of composites easier (usually). Use the dynamic range compounding preset around the effect if the effect is 8 bit.

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Liz McLean Knight
Re: "Light" leak from glow effect on supposedly masked object
on Sep 3, 2018 at 7:21:12 pm

Thanks, Andrew! I made the two masks +2 and -2 in "expansion" and that did it. Phew!



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Andrew Somers
Re: "Light" leak from glow effect on supposedly masked object
on Sep 3, 2018 at 8:10:53 pm

Cool! Glad it worked!!

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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