Need help on tricky light bulb chromakey

[Serge Tsipis]

Hello!

I'm doing some VFX footage that includes a light bulb being screwed in and turned on with a green screen background. I did a test shot and found myself in a trouble. Well, maybe it's just my lack of experience in chromakey, so I'd really appreciate experienced VFX-ers input!

Here goes the storyboard:

1 - empty socket

2 - hand goes in, screws in the bulb

3 - bulbs lights up

4 - hand goes out

My main concerns are:

1. Should I use blue screen instead of green to get "further away" from yellowish tungsten bulb?
2. Should I grip the socket on a stand (not getting into a hand's way to avoid rotoscoping) and move background away to get rid of shadows and casts?
3. What can I do to avoid hue shift when the bulb goes on? Light it with the same colour temperature sources?
4. How should I deal with a transparent part of the bulb? It's difficult to see it on tiny pictures, but there is quite a bit of it in the upper left part of the bulb.

And some additional info:
The bulb should be located with slight angle like it's pictured, I cannot change it to get rig of a transparent part. I'm gonna shoot with my R1MX at 4K 16:9 25fps RC42.

I hope someone can help me, because I feel like it's gonna be easier for me to film just the hand with dummy bulb (painted blue + tracking markers) on a green screen and draw the rest in Cinema4D + Mocha Pro

Cheers!
Serge

 

[Björn Benckert]

So what is the background going to be?
As you now got it set up you it's done as if the background is a none reflecting board thats sitting right where you have the green screen. As your setup is capturing shadows and light onto the screen... you also go a big hole for the socket of the lamp... is that supposed to be?

I think blue would do better as your lamp is very warm and does not fall far from the green screen color.

Your green tracking dots is not needed they only disturb the light fall of so take them out.

To key this you would get the best result with the autodesk flame modular keyer. Using a combo of difference matte between no light / light with no hand / light with hand and shadows. together with the a mster keyer node and some pixel fill for the hand.

To key it out nicely without adding the background as a surface placed where the greenscreen is... Well then I would say, splines are what you will be working with and the result will be quite poor.


any way to give any good advice we would need to know what the comp is supposed to look like.

 

[Gavin Greenwalt]

1. 6 one half a dozen the other in this instance.
2. Do you need the shadows and light pattern to composite onto a CG background?
3. Yes. If you need the light bulb to match your key light I would gel your key to match.
4. What is this going to look like ultimately? Is it going to be on white? Black? CG background? Do you have a storyboard for the final comp? If I could see what your desired end product is there could be an easier way all around to do this.

 

[Serge Tsipis]

Thankyou guys for chimeing in!

The final comp is gonna be a yellow and black CG letters. I'll try to post the plate when I have it. In a few hours, I guess. I think I don't really need the shadows/casts for the comp... Or I can recreate it if needed. Those "tracking markers" are useless, I know. It's just there, so I considered it not to be an issue since the shot is stationary. It will be "zooming out" in final comp, when the bulb is lit and hand is out of the frame. I'm on MacPro platform and my toolbox is FCPX, Mocha, Resolve, C4D, Motion, Nuke (sometimes), Adobe.

 

[Björn Benckert]

Thankyou guys for chimeing in!

The final comp is gonna be a yellow and black CG letters. I'll try to post the plate when I have it. In a few hours, I guess. I think I don't really need the shadows/casts for the comp... Or I can recreate it if needed. Those "tracking markers" are useless, I know. It's just there, so I considered it not to be an issue since the shot is stationary. It will be "zooming out" in final comp, when the bulb is lit and hand is out of the frame. I'm on MacPro platform and my toolbox is FCPX, Mocha, Resolve, C4D, Motion, Nuke (sometimes), Adobe.

If thats the case then my sugestion is to make the fixture for the light bulb stick out far from the chroma screen. Also use blue screen instead of green. And light the bluescreen seperatly and when you have the shot the sequence you turn of the blue screen lightning and possibly change the screen from blue to black and shoot a plate with the light bulb lit and with the light bulb not lit.

The black passes can then be difference keyed against each other and the result can be comped with a "screen" or additive transfer mode. i.e you get only the flair / light from the bulb added ontop of your CG letters.

The distance between the light bulb and the blue screen is important to make sure that your hand etc does not cast shadows on the blue screen.

also make sure the blue screen is light enough to have a good exposure in the blue channel. the bluescreen lit should land somewhere right above the middle of your histogram at 800iso. And do light it with daylight/ non tungsten light and preferably even gel the screen lights with blue gel. Then that will give you an exelent separation from the rather warm hand and light bulb.

 

[Dr. Sassi]

One more way to do it:

I never had that problem, but you have two different backgrounds and perhaps the IBK Keyer might help here. As you can get two "clean" plates (light off and on)

Google: NUKE, Basic Workflows, Image Based Keyer (IBK) Steve Wright. There are several video links available.

You need to combine then both results to one "mask".

 

[Serge Tsipis]

Here are the previews I got from the designers:

The letter:

and whole set "zoomed" out:

I think I gonna try this with the blue screen first. Looking at the previews, I don't think I'll need the shadows from the hand and flares from the bulb... Will see if I can grip the socket stiff enough not to shake during the action. Maybe will test it with the same setup and blue screen first.

Thanks for you input! More advice is welcome since the job isn't done yet I'll keep you guys informed on how it goes. I really appreciate your help.

Cheers!

 

[Björn Benckert]

Shoot, upload trimmed r3d's and post link here… then, most likely, I think it will sort nicely.

 

[Gavin Greenwalt]

I am going to disagree with Bjorn on this one. If you move the screen back you'll still have to wrap your lightbulb socket rig. Now you have two different bluescreens and I always end up with an obnoxious edge between bluescreens that requires more fiddling than the shadows in the first place. Shadows can be garbage masked pretty easily. Then again to do this at a really high quality I expect there's just going to be plenty of roto no matter what. If you can get your socket free floating without any green wrap I would be very surprised--but then yes you can move your chroma panel back a ways. It'll probably jiggle too much though. Definitely remove those tracking markers though whatever you do.

IBK won't really help much in this case. It's really good for things like lace but not great for this kind of thing. Just remember that however you shoot it, don't try to get everything in one key. No one key is ever going to solve every problem. Break it up into similar chunks and key each with the best approach and keyer then keymix them.

 

[Jeff Kilgroe]

Why comp this? Why not model/ render realistic lights for your lettering? Shoot the hand going in and installing a real bulb. Light it in CG.

 

[Serge Tsipis]

Jeff, that's what I was thinking... But I'm gonna try it with a blue screen first. Just to know the difference.

 

[Jeff Kilgroe]

Given the black screen, gold letters, I would probably shoot this against a black background, if you still go practical vs. CG. I'd try it a couple different ways.

 

[Serge Tsipis]

Finally, It seems like I've been able to pull off a good key using just 4 nodes and a few keyframes in Resolve... So I guess, the whole issue was just my lack of experience in chromakeying. Anyway, thank you guys for your help! Will see which route it will go on a real shot in a few days.