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LED Lit Green Screen & Halo Effect

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Jonathan Clauson
LED Lit Green Screen & Halo Effect
on Apr 11, 2010 at 3:48:38 pm

Good morning all!

I just got in some footage to edit from my client who bought the latest and greatest thing, the new LED Green Screen setup and I am having an issue with it and I wanted to get some thoughts.

The setup is a simple 2 camera talking head piece, but when I key it I get all kinds of trouble with the "halo" you see around the subject.

My guess is that if the LED Rings are located on the lens, as most of these setups recommend) then what I am seeing is a shadow from the ring on the main camera to the green screen on back as the subject is either absorbing/blocking the light. I see the same effect on the promo video for the product.

My question is if there is a way to get around this by maybe placing the ring on the ground behind the subject or putting it on a c-stand higher up to reduce shadow. I am sadly 1,000 miles away from where they shoot this so I can't really experiment so if anyone has any experience with this setup I would appreciate it. Thanks!



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Mark Suszko
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 1:49:20 am

No this was not shot with the special green LED-ring-based system I know of, at least I don't believe it was. If it was, the entire screen behind him should have been the same shade of green. That looks more like conventional green screen cloth, not the retro-reflective stuff, and I think I can even see a vertical seam in the cloth on screen right. Now, your guy might have shot with a white light ring around the lens, but that ugly edge effect is not caused by that.

That edge noise looks mostly to me like artifacting from DV compression; tell us what format this is shot in, what codec, what your settings are in the editing/keying software timeline. Etc. If this is DV footage, well, you're going to have some trouble, and we can work you thru some step-by step things to try and get a better key, but first we all have to know what exactly we're working with here.


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Todd Terry
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 2:44:16 am

I'm going to go out on a limb here and do something I rarely do... which is differ with Mark's almost-always spot-on opinions (and Mark might indeed be right here, but I'll offer a differing theory)...

I think that, yes, this was indeed a LED-ring lens-based system with a glass-bead reflective background. I believe that the halo comes from the talent being too close to the screen. I know you weren't on location, but do you know how far in front of the screen the guy was standing? My guess is that he was too close to it (maybe even right up against it, almost), which would cause the portion of the screen very nearest his edges to be illuminated from the LEDs on only one side of the ring, not from both as they would if he were futher back. His body is basically causing the equivalent of a shadow from half of the LEDs as he is blocking their reflection.

I'd suggest moving the background back a bit deeper and see if you can get better results.

By the way, you say that you think the ring was on the lens "as most of these setups recommend." Putting the ring on the lens is not just a recommendation... it's an absolute requirement. These things work by reflecting the green light directly back at the illumination source... ergo, the illumination source (the LED ring) must be precisely in the same axis as the camera is shooting, or it will be bouncing that green light back somewhere else and not at that camera. Your suggestion of "placing the ring on the ground behind the subject or putting it on a c-stand higher up to reduce shadow" won't work either, for exactly those same reasons. The farther the ring is from the axis of the lens, the less green the camera will see. If you put it completely off camera (i.e. behind the subject or high on a C-stand), it'd be unlikely that the camera would get any of the green reflection at all. It must be on the camera lens.

That is, in my opinion, one of the biggest downsides of these reflective greenscreen systems (besides the expense)... since greenscreen work is one of the most common scenarios when you will also have a teleprompter in use, and you can't put an LED ring on a prompter-rigged camera.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Mark Suszko
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 5:17:33 am

Todd said a lot of what I was thinking, vis-a-vis how moving the ring off-axis, as if it were another conventional light, will not work, if this is indeed the Chromaflex system they are using. I just didn't bother bringing that part up in my previous answer because I still am not convinced this was a Chroma-ring-made shot. The reason why is also from the same thing Todd says: the retro-reflective cloth only sends the light right back towards the lens, so a shadow from the LED system is not possible unless perhaps the guy was literally laying atop the screen material. And I'm also perplexed by why there's a dark section of the cloth on the left hand side: unless there is some kind of incomplete crop or matting going on there, it makes no sense for that section of cloth to not be the same color as the rest. You can see it is one piece of cloth being clamped to a frame to make it tight and flat, and you can see a vertical seam on camera right where the cloth is joined to make it wider. Chromaflex doesn't look like that, far as I can recall.

You *could* see that kind of shadow if the light source by the lens is normal white LED's, the guy is too close to the cloth, and the back cloth is normal green screen cloth, though. However in that case you would probably also see more green spill on the actor than we do now. And I remain convinced that's what it looks like to me right now, and that this is a conventional chromakey shot just in a degraded codec form like DV25.

This is very puzzling, and it shouldn't be. I feel like we don't have complete understanding of what we're looking at here.

Is there a close-up shot with more detail you can put up a second still from? Or can you call up the guy and get more detail on what was done on set?


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Dennis Size
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 6:27:50 am

It's interesting that there's so much controversy over the greenscreen itself when the lighting on the talent is "God-awful" to begin with. If the talent were anybody important no one would really care about the greenscreen -- they'd be worried about their talent walking out because they look so bad.

To throw my 2 cents into the mix however, I agree with Mark. I can't believe it's the reflective system either.
This just looks like badly lit (perhaps with the white LED ring lights) greenscreen. That seam is too obvious, and I've never seen anything like that when using the system. It actually looks like the two piees of green fabric were sewn together with the nap running in opposing directions.
I also didn't think the system could work with 2 cameras cross-shooting. Please post the shot from the reverse camera angle.

DS




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Jonathan Clauson
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 4:19:27 pm

Thanks for the information all. I only did a cursory glance at the LED tech so I should have known about the LED ring having to be right on the lens itself. The fact that I could pull a key from cam 2 was what threw me.

The footage was shot on HDV 1080i 60i on two Canon Hh-A1'sand one A1S. However the project is for SD broadcast so I imported the footage at DV/DVCPRO-NTSC Anamorphic. If I did this wrong as well please tell me as I am coming back to editing after a 3 year hiatus. :-) I am also on FCS 3 with FCP 7.02 for reference. I have the original DV Tapes as well so I can recapture with a different codec if it is recommended.

The background is the chromatte fabrics from reflecmedia and the line is just part of the larger canvas they sell according to the DP on set. The line hasn't been an issue however even in noise removal.

I have 4 screen shots uploaded with the 1st and 2nd cam. The 3rd is a shot with no spill suppression or noise removal, just a solid matte. The 3rd is my attempt to cut down on the noise and you can see the issue I am running into with it cutting out part of the subject. I have also included my settings as well incase I am royally fracking it up.

Thanks so much everyone, this is the best board community ever!

- Jonathan

Camera 1


Camera 2


Primatte RT Unadjusted


Primatte RT My Best Key (might not be so good, you tell me. :-)



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Mark Suszko
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 5:34:02 pm

I think I would prefer to do the chromakey in the native format you got out of the camera, then bring that element into your DV25 workflow if you have to do DV 25. DV25 sucks for graphics quality and especially for keying, as you're working in just a 4:1:1 color space there. Try the Primatte again on the footage in a high rez codec and I bet your result looks better. Another tip based on my own experience keying in Dv25 is, you can apply multiple passes of the keyer, so first of all concentrate on sampling the key right along that fuzzy edge by the body. The rest will be easier to fix later on a second pass.


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Jason Jenkins
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 4:27:34 pm

I'm going to have to side with Todd on this. I have a Chromaflex system and it is indeed possible to get this kind of result. I'm 99% certain this was shot with the Chromaflex system. The dark halo can be minimized by experimenting and altering the talent to screen distance and the camera to talent distance. LED brightness is a factor here as well. I don't know what you are keying with, but even with some halo, I've been able to pull good keys with Keylight in After Effects.

Jason Jenkins

Flowmotion Media

Video production... with style!


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Jason Jenkins
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 4:41:45 pm

Here is a document that describes the problem and solutions in detail: http://www.reflecmedia.com/files/downloads/15/1/HaloShadow.pdf

Jason Jenkins

Flowmotion Media

Video production... with style!


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Mark Suszko
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 4:51:24 pm

Well, I learned something new today. And confirmed as well that I won't be getting one of these rigs anytime soon! :-P


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Dennis Size
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 5:07:18 pm

Whew....another dilemma solved here on the Forum.
The next -- and more important -- step is to make sure the terrible lighting on the talent gets improved.
DS



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Jonathan Clauson
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 5:29:12 pm

Hi Dennis,

I am sadly not the DP on the shoot nor am I truly an expert on lighting so any advice you would like to give would be appreciated. It seems you have an idea on what the setup should be, so if you can let me know your thoughts I will relate the info to the DP. :-)

Thanks much!

- Jonathan


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Dennis Size
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 6:04:48 pm

Much like the physician who can't prescibe medicine -- or do surgery -- based on a phone call with a patient .... I'm not about to relight anybody else's work, or make suggestions, without seeing the space -- or a graphic representation ( or for that matter, payment).
The sad thing is, you say a D.P. is actually lighting it. I will reserve my harsh judgement for that D.P.'s work and merely say, if he's calling himself a D.P., then he surely must know the best ways to light something -- and must have consciously chosen exactly how he wanted his talent to look.
DS



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Jonathan Clauson
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 6:13:17 pm

Hi DS,

You make a good point and I'm sorry for any offense.

I say DP only out of habit for the person who sets up the camera/lighting/etc. The person on this shoot is new and not a DP and does not claim the title so there it is. :-) He is from a live/theatre background and bought new toys and I think is learning how to use them (this was his 2nd time giving me footage with the LED green screen rather than the traditional set up which never had the issue).

I am going to go back to the books and do as much research as I can on lighting for LED setups and when I visit the set next month hopefully we can make something work better.

Thanks much!


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Todd Terry
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 5:35:40 pm

Hey Jonathan...

For what it's worth, I took your still and was able to pull a pretty perfect key off of it using Ultra2 matting software. Now, that doesn't always mean the key would stay as perfect when dealing with real moving video, but my guess is that it would. Keying the still cleanly wasn't challenging at all.

Have to agree with Dennis, too... irrespective of the background, the lighting on the talent is just god-awful. I know you are a thousand miles from where the actual shoot is, but yell at them about that if you can. It will make your job easier and give you a better end result.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Jonathan Clauson
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 6:03:22 pm

Hey Everyone!

Thanks so much for all the feedback and ideas. I still have a lot to learn and I appreciate the candid responses.

I found the manuals and everything for the LED rig and will pour over them tonight and make sure the lighting setup they are using matches what their setup.

As for the key, I think I finally nailed it so all should be well after I encoded it at its native HDV format and then dropped it down to DV after that.

Thanks again all!


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Mark Suszko
Re: LED Lit Green Screen & Halo Effect
on Apr 12, 2010 at 6:49:01 pm

Tell the DP that the ring light for the chromaflex backdrop can't be the keylight for the talent as well: you still need to light the talent separately.


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