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Forums Adobe After Effects “Add” Blending mode darkening edges unless BG layer exists

  • “Add” Blending mode darkening edges unless BG layer exists

  • alex ezorsky

    August 4, 2022 at 6:41 pm

    I want to add wavy glowing lines to my character who is keyed out. I place my black and white wavy lines video over my character clip and change the blending mode to “add”. It works of course, but the black areas of the wavy lines clip still exist since I have no background and it doesn’t know what to “add” to over transparent areas. So I try two methods to make the wavy lines alpha match my character:

    1. Preserve underlaying alpha

    2. Duplicate character layer, place it above wavy lines clip and use duplicate as an alpha matte for wavy lines.

    In both cases what I end up with are darkened edges around my character as long as there is still no BG layer. Once a BG layer is added underneath things work fine and edges look great.

    I would ideally like to export an alpha transparent video of my character with the glowing lines and no BG without the weird dark edges.

    Thanks for the help!

  • Max Haller

    August 4, 2022 at 10:05 pm

    I believe you understand how its working properly. The bit about it not knowing what to add that layers pixel data to because there’s nothing underneath.

    Have you tried using the choke matte effect to shrink the edges of the alpha? That could be enough to get rid of the dark edges if you play around with that and maybe a blur. Try choking the layer youre using as an alpha matte with that effect just a few pixels and it might be enough.

  • alex ezorsky

    August 5, 2022 at 2:29 pm

    Thanks for your reply. While technically choking the matte works, it’s not perfect as there is always either a little too much choking (causing the effect to not truly reach the edges of the layer) or too little choking causing the slightest darkening of edges.

    CURRENT SOLUTION: for anyone else struggling with this the only thing that seems to truly work is to use the wavy lines effect as a luma matte for an adjustment layer which I then place above my character and add to it a brightened curves effect. This would of course work the same if I replace the adjustment layer with a duplicate of my character but I prefer adjustment layers when possible. Bright lines and no darkening

    EPILOGUE: I would still love if someone at Adobe could give me like a root level programming explanation for this, I feel like this borders on a bug. Blending modes over semitransparent pixels (I’m guessing the semitransparent pixels at the edges of alpha are the culprit here) should still only do what they do over opaque pixels, i.e. only “add” if using “add” and not also darken. Rant over.

    Still happy to hear thoughts though!!!

  • Robert Müller

    August 8, 2022 at 4:54 pm

    Hey, yeah this has been an issue for ever and seems to be a core problem for every compositing software I used (e.g. Nuke). We used to have this problem with 3D renderings, here is my workaround (I hope I remember everything right. Real footage might give you some problems but I cant try it out right now)

    I usually go as follow:

    – precomposed the masked out/ keyed out footage, so you have one layer with no effects and masks, containing an alpha channel

    – apply the min/max effect set to maximum and “RGB+Alpha”, you dont have to go wild. This is to “expand the edges a little.

    – duplicate the layer and remove the effect (as I write this I realise, that you dont have to duplicate the original layer. A CC composite effect should work just fine)

    – above this goes the footage you want to screen/add/ whatever

    – on top of the stack goes another copy of the precomped footage with no effetcs, blending mode set to “Stencil alpha”

    Ive attached screenshots (sorry for german UI) to visualize the order better and a comparsion to your “old” method

    There a different ways to expand your footage a little bit, but this always worked for me. Hope I could help you out 🙂

  • Tristan Summers

    August 9, 2022 at 12:23 pm

    I am not sure you ARE understanding things properly.

    I would duplicate the person image and use tha as the matte for the wavy add layer.

    That is what you would do in any compositing software to limit the edges.

    I would Change the Transfer Mode of the wavy lines to Preserve Luminosity, then add a Shift Channels effect and take the alpha from luminosity, which is a nicer way to do it.

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