AF100-Atomos Samurai: first test...buzzing artifacts major problem...

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Nicholas Natteau

Veteran
So after formatting my SSD drive and making sure I had the latest firmware, I went ahead and did my first AF100 chromakey test shooting at 1080p24 Apple ProRes HQ on the Atomos Samurai.

But for some reason my results are just as bad as when I was shooting green screen with the native AVCHD codec. I'm sure it's something I'm doing wrong. Yet I made sure to dial down the Detail and Vertical Detail in my AF100. I'm also shooting HD Normal not Cine Gamma D or V.

After chroma keying with Keylight 2.0 in FCP7, I'm getting terrible buzzing artifacting around the edges of my subject and now even on the subject's hair. I can't understand the buzzing issue, because this is Apple Pro res HQ.

Please see this sample:

http://vimeo.com/36107405

Will try more tests later today.
 
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Quite simply you are either getting some green spill on your subject around the fine edges OR your screen may be just overlit compared to your subject. Either or both of these combined are causing your issue.

How far from the screen is the subject? How are you lighting the screen? Whats your set up? Thats where your issue is.
 
Hi Noel, thanks for replying. My green screen is lit by two Litepanels 1x1 floods to eliminate shadows, and the mannequin itself is lit by one 1x1 Litepanel spot as a keylight. I also have a Reflecmedia chromaflex that I plan to use to see if I get better results. I wanted to try first with a traditional muslin green screen. The mannequin test subject is about 2 or 3 feet from the screen.
 
Nicholas Natteau said:
Hi Noel, thanks for replying. My green screen is lit by two Litepanels 1x1 floods to eliminate shadows, and the mannequin itself is lit by one 1x1 Litepanel spot as a keylight. I also have a Reflecmedia chromaflex that I plan to use to see if I get better results. I wanted to try first with a traditional muslin green screen. The mannequin test subject is about 2 or 3 feet from the screen.
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Hey Nicholas. Well there's your issue right there. From your cameras perspective and some of this is speculation as I dont have any idea how close your lights are to your screen or to your subject - but youve described to me tells me A/ Your screen is going to be overly bright, impossible to say how much without knowing exact details and your subject is way to close to it.

Is space the issue? If so maybe the reflecmedia is a better option for this head/shoulders type shot.
 
Hi Noel, thank you again. So the buzzing/artifacting is the result of the bad lighting? I used to think that the buzzing was due to the compressed nature of AVCHD at 24 Mbps and I thought that recording as Pro Res HQ would eliminate the buzzing issue.
 
Nicholas with keylight within FCP7 I can pull amazingly good keys when lit properly with the AVCHD direct from the card.
 
Hi Nicholas,

Chromakey work is an art in itself. I have worked in the FX industry since the early 90's and let me tell you that not much has changed since then with respect to techniques. It's much easier today with the higher resolution cameras and codecs for sure, but lighting is definitely key. I remember when the HVX200 came out in 2006, and someone posted some well lit footage. I downloaded it and made a great comp.

http://10framehandles.com/movies/HVX_Comp_BobGundu.mov

Poor guy. I have no idea who this guy is! Anyway, shooting on the Samurai is not going to miraculously get you better key, if you have green spill all over the talent or if the screen was badly lit. The native codec on the Af100 will handle the keys very well. Your issue is different. You should post the original file. Also, shooting at a shallow DOF doesn't help either. What was your aperture set at? How about your ISO?
 
Nicholas Natteau said:
Thanks Shooter, but is the buzzing then all the result of the lighting issue and nothing else?
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Yes absolutely definitely ....plus maybe your keying skills in post contribute to your issue.

as bgundu says... its an art to light a key ....(but it aint rocket science)

You light the subject as you would any subject ..then you light the BG to ensure that you can pull a key from it.

The subject lighting and the BG lighting then consider the basic rules of "chroma keying"

Separation, saturation!

Separation is the distance from the BG to avoid spill on the subject...as well as "difference in color" between subject and key BG.

Saturation is the amount of pure key color in the BG. That is exposure related.

BTW - dont be discouraged. The Samurai is still going to provide better key clips than the internal clips.
 
Hi bgundu and thank you very much for your feedback as well. I was using a Zeiss Prime ZF mount 50mm lens at aperture 2 or 2.8 I believe. It was not fully wide open at 1.4. I was also shooting at the lowest ISO possible on the AF100, ISO 200.

Could you tell me what AF100 settings you use for green screen shooting? I posted this question elsewhere in the AF100 forum but got no feedback and I'm sure a lot of other AF100 users would love to know this. I was told to dial my Detail and Vertical Detail settings all the way down to -7 and not to shoot in Cinegamma D or V but instead in HD Normal.

As you know there are so many AF100 settings: Knee, Detail, Vertical Detail, Gain, etc. I read the AF100 manual and even googled this but didn't find any information on recommended AF100 settings for green screen shoots, (besides the golden rule of having a well lit green screen scene.)

But why is it that all this buzzing noise appears only after Keylight 2.0 is applied. The buzzing's not there in the unkeyed footage, only when I apply the chromakey.
 
I find the detail down to -7 is too aggressive. I prefer around the -4 mark. HD Normal is a good setting for the too. F2-2.8 is still a bit to shallow. Ideally you want to be around a minimum of 5.6.



Nicholas Natteau said:
Hi bgundu and thank you very much for your feedback as well. I was using a Zeiss Prime ZF mount 50mm lens at aperture 2 or 2.8 I believe. It was not fully wide open at 1.4. I was also shooting at the lowest ISO possible on the AF100, ISO 200.

Could you tell me what AF100 settings you use for green screen shooting? I posted this question elsewhere in the AF100 forum but got no feedback and I'm sure a lot of other AF100 users would love to know this. I was told to dial my Detail and Vertical Detail settings all the way down to -7 and not to shoot in Cinegamma D or V but instead in HD Normal.

As you know there are so many AF100 settings: Knee, Detail, Vertical Detail, Gain, etc. I read the AF100 manual and even googled this but didn't find any information on recommended AF100 settings for green screen shoots, (besides the golden rule of having a well lit green screen scene.)

But why is it that all this buzzing noise appears only after Keylight 2.0 is applied. The buzzing's not there in the unkeyed footage, only when I apply the chromakey.
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I will chip in here as well.

I can pull a key using default presets on the AF100. I showed you some examples ( in a post).

The "buzzing" is poor lighting for a key and poor post prod keying skills. Both areas require proper technique.

Search up a tutorial in both these areas.
 
Nicholas,

That chatter on your keying sample looks like a combination of spill and noise.
+1 on what Shooter and others have said about lighting properly and getting the subject away from the screen. (Did you watch those Alex Lindsay videos I linked to on the other thread? They will teach you best practices fast.)

Also, as previously stated, shoot with the lowest ISO possible, to reduce noise.

Keying is a complex process, especially since there are so many tools to choose from. There are many good keyers available, some with very different technologies under the hood. Also, there are keying aides like Composite Wizard and Key Correct from Red Giant that give you more options.

You shouldn't expect a one-click solution. Most keying takes a fair amount of work.
 
OK so after doing some more tests, because some of you had questions about my setup, I wanted to post some photos hoping you can help me understand what I'm doing wrong in my setup.

Here's what I don't understand. In photo #3, I have the Reflecmedia Chromaflex screen turned on as well as my three Litepanel 1x1s, and the line on the waveform is perfectly thin and level at 50 IRE.

But after inserting the mannequin into the scene, look what happens to line on my waveform monitor (photo 4)...all of a sudden the line is thick and uneven.

You can see from my other stills that the mannequin's head is perfectly in focus. My lighting setup consists of a keylight Litepanel 1x1 spot and 2 Litepanels 1x1 floods to light the subject from behind.

Please tell me what I'm doing wrong from these stills.

Last point, not sure how to get the Chromaflex straightened out. It was folded in its bag for a month and is now not properly straight as you can see from the side in photo #1.

http://gallery.me.com/nicholasnatteau#100469
 
Subject is too close to screen
Subject is slightly over exposed
No back light on subject - its all green bounce

Subject appears slightly green pallored - probably from the green carpet

Subject has two nose shadows- both parallel to her nose

Screen is too bright - get it down to about 30% on the wfm


You probably have a lot of light flaring the front of your lens
 
Thanks very much for pointing all this out Shooter. Will run more tests. But I was told that when using Reflecmedia Chromamatte or Chromaflex, that the subject has to be as close to the background as possible. Is that not the case? I know with traditional screen screen (muslin, etc) the subject has to be at a good distance from the screen.
 
Shooter said:
:shocked:

Maybe some one who has can chip in on how best to work theem ...but it seems to defy proper keying techniques and principles.
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Right - when using the Chromatte or ReflecMedia system, it really does stand conventional keying on its head.

There should be no green spill, for example, because the fabric is designed to reflect the light from the LED exactly parallel. As such, the lighting on the mannequin shouldn't be affecting the waveform of the screen alone.

As for distance to the screen, you typically want to put the subject as close to the screen as possible (which is the EXACT OPPOSITE of what you want to do in conventional greenscreening, where you want the subject as far away from the screen as you can possibly get it!) The reason you need the subject close to the screen is because the further away the subject is, the thicker there will be a gray halo around your subject (which is caused by the green light from the LED not reaching the screen, it's blocked by the subject).

As for green light on the subject, that's pretty obvious (and one reason I really don't care that much for the Chromatte/ReflecMedia stuff): the system requires you to shine a green light on your subject! There's a ringlight around the lens emitting green light directly onto the subject.

The ReflecMedia type of systems can work well in confined spaces where you simply cannot get the subject separated from the background. Other than that, I think conventional greenscreening works better. If there's space where you can put a lot of distance between the subject and the screen, you'll usually (I think) get better results out of conventional greenscreen. But in tight quarters the reflecmedia stuff has a big advantage.
 
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