Blackmagic Forum

Using Fusion inside Resolve, I pulled a key on this shot. The matte appears to be solid, but I still get chunkiness in the image. What's the best way to solidify a matte for green screens?

I just watched Alexis Van Hurkman's "New Resolve 15" Ripple Training features tutorial video over the past week, and one of the things he outlines is the need to pull 2 separate Delta keys to do the chromakey: one is a more subtle key made to get all the bits of hair and other outside detail on a person, and the other is a harder-edged key for everything inside. The idea is that the latter will get rid of any "holes" trying to push through in the key.

I suspect this is what you'll need to do. One key may not be enough for these situations. We could do similar things using the Key Mixer within Resolve.

Thanks, Marc.
Funny, I bought that from Ripple a while ago, but haven't gone through all the videos, yet.

Thanks for the heads up.

It's common practice with VFX artists to use more than one key for greenscreen, like layering keys with their parameters optimized for specific areas of the foreground object.
It's pretty rare to get footage that allows a one-click solution, in particular not if there was no VFX supervisor when shooting…

The issue was still there even after I combined the second Delta Keyer. So, I ended up rotoscoping the areas of the shot where there were similar artifacts and Merged it on top. Thankfully, the actor isn't moving all that much, so I think it will work.

Uli Plank wrote:It's common practice with VFX artists to use more than one key for greenscreen, like layering keys with their parameters optimized for specific areas of the foreground object.
It's pretty rare to get footage that allows a one-click solution, in particular not if there was no VFX supervisor when shooting…

Hi Uli,
Oh yea, I am aware of that. I kept it simple at first because the shot will end up as a screen insert on a "TV" screen, so it will be much smaller than its original size. But, I really wasn't happy with the artifacting, since I knew the director would say something. So, I decided to tackle it anyway. As I mentioned above, even with the secondary key, I still added rotoscoped areas of the footage on top since the "hole" still appears. I think it will work for now, given its end use.

This can be a combined key-despill issue. Pull and combine your alpha as necessary and inject it into footage despilled without messing alpha. Premultiply in the end.

Hendrik Proosa wrote:This can be a combined key-despill issue. Pull and combine your alpha as necessary and inject it into footage despilled without messing alpha. Premultiply in the end.

Can you show me what that looks like in a node view? I don't understand it. I'm still relatively new to Fusion, so I'm winging it most of the time based on my experiences with Nuke.

Thanks.

Todd Groves wrote:Can you show me what that looks like in a node view? I don't understand it. I'm still relatively new to Fusion, so I'm winging it most of the time based on my experiences with Nuke.

I'm not behind the desk, but in Nuke it would be two different branches, in one do your key and other alpha related stuff, in another do despill, then with Copy copy alpha to despilled image and Premult. Premultiplying is necessary because any merge operation after this expects RGB channels to be premultiplied, without it you get bright halo. For Fusion just convert this to Fusion node equivalents, Premult is Alpha Multiply and Copy/ShuffleCopy is Channel Boolean.

The main point is to keep your alpha processing separate from despill operations. Nodes that allow doing everything in one step (like Delta Keyer) are nice for some fast stuff but if you need more control separating alpha and despill is the way to go.

Thanks, Hendrick.

I ended up setting spill to Source, which rid of most of the problem. The end use of the shot will be on a TV screen insert. So, what shows now will probably be too small in the final shot to notice. If it were a shot that filled the frame, I would spend more time on it for sure.

I'll experiment with your solution aside from the project itself, so I can get better acquainted with the process.

Thanks again.