Imported green screen video has weird dark outline when imported into Blender

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1

Hi,

I chroma keyed a green screen video in DaVInci Resolve, then imported it into a blender scene as an Emission node so it’s not affected by lights in the scene (I just change emission strength to match the scene).

In DaVinci, the key is fine, and there is no weird dark outline. But when imported into Blender, it looks like the following:

blender outline problem
blender outline problem1042×361 91.1 KB

I messed with every material setting that had a positive value, and it changes nothing.

Why is this happening, and how can I fix it? The only thing I can think of is that there’s something wrong with the codec I used to export the keyed video from DaVinci, or something’s up with Blender.

If it helps, I used the GoPro CineForm RGB-16 bit codec with Alpha export on, and that’s the only codec with an alpha channel available for me on this computer, so I can’t test other options.

Thanks!

2

You may want to use the alpha to mix with an additional trasnsparent shader (or even bluring the alpha). It also depends on eevee/cylces and alpha blend modes/ tranparency light path max bounce values.

3

There are two ways to export a clip with an alpha channel: 1) Straight or 2) Premultiplied. In Blender you can set the corresponding alpha treatment in the N-panel of your shading node in the “Alpha” dropdown menue (“Straight/Premultiplied”).
I hope this can solve your problem.

Markus

2 Likes
4

Markus is right, this looks like a straight vs. premult issue. Resolve is interpreting it correctly while Blender is likely defaulting to the wrong option.

1 Like
5

First off, thanks for the replies! I’m very grateful you even replied.

And I tried everything you all said, but it didn’t change anything. And for everything that follows

  • I’m using cycles.
  • I set the video’s Material Properties → Viewport Dispaly → Settings → Blend and shadow modes both to Alpha Clip.
  • Turned the light paths max bounces all the way up to 5+ for everything. Even though there’s nothing that would get in the way to prevent light from passing through, etc
  • Set Light paths → Clamping both to 0.
  • Set the alpha in my video’s node in the Shading tab’s N-panel to both Straight, and Premultiplied.

But nothing stops this black line from appearing.

And as for Okidoki’s suggestion, this is the node structure I set, but nothing worked either:

  • my_video’s color → PrincipledBSDF emission
  • my_video’s alpha → MixShader’s Fac
  • Transparent BSDF → MixShader’s top shader
  • PrincipledBSDF → MixShader’s bottom shader
  • MixShader → MaterialOutput’s surface

Any ideas? Need some more info?

6

I forgot to show that this is the original node tree:

node tree - black outline
node tree - black outline714×538 62.3 KB

7

FIXED IT! The problem was the original key. I ever tested that key against a white background. It was always either black or transparent.

So I fixed the key, and it works fine now.

8

Glad you found a solution :tada: . Interesting a specific keycolor could give good results in the original app and on the other hand can give problems when exported to blender… :thinking: hmmm while re-reading your first post i also think a bit different about my understanding of your problem description… Maybe next time i would ask something like: “Any reason why not doing this alltogether in blender? Because sometimes exports and re-imports break the workflo.w…”