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Old February 15th, 2010, 10:34 PM   #1
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"High-end" green screen shot with the EX1

Iím preparing to shoot an all green screen project. Although I have shot green screen several times with my EX1 this will be my first all green screen job and it will be shot on a cyclorama type of stage instead of just a green backing and we have decided to go as high-end as possible with the EX1. Also, so far I have always shot to the SxS cards and it keyed fine. But for this one I have decided to use the HD-SDI out to get 10bit 4:2:2 for better keys.
My questions are:

1. What is the best solution to capture the HD-SDI signal of the EX1 using a computer? I guess what Iím asking is how should I capture it and using what codec? Or should I capture it fully uncompressed? The solution needs to be computer based. Iím not interested in one of the portable solutions like the nanoflash etc. I donít need the portability since I will be in a studio and I hear I have more options capturing to a workstation not to mention it will end up being cheaper as well.
2. Does it matter what gamma, matrix and other settings I use? If so what are the best settings for green screen?
3. It is better to turn detail OFF right?
4. Is it better to use daylight balanced light for the screen and for talent?
5. What about matchmoving with the EX1? Is the CMOS a problem? Any experiences?
6. Any other tips and advice on shooting with the EX1 for green screen is greatly appreciated.

Thanks!
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Old February 16th, 2010, 09:58 AM   #2
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OK...first, try to NOT have the cyc painted around the sides if you don't need that range of movement. I recently worked on a music video where the studio painted around the cove so we had a space that was about 30 feet wide, but side walls that extended about 15 feet forward with the green.

There were drums.

Drums with chrome.

sigh.

Anyway...after copious application of Arrid XXXtra dry (high powder content, water soluble, you can spray it on virtually anything without damaging it and wash it off without residue unlike dulling spray) we were OK...but lighting and compositing were a bit more challenging than they would have needed to be.


For light, I prefer daylight sources for green screen for the following reasons:

From a post point of view, color keying usually employs something called "spill suppression" to handle any reflected light on edge transition areas. This feature is particularly useful in attacking hairs strands and that sort of thing which you would like to remain visible, but you need to de-tint them.

The way a spill suppressor works is to take the color you are removing into account and "add back" the color that is phase-opposed to a variable region around the edge of the key. With green, you would add magenta...with blue, spill suppression adds yellow (one reason why keying humans aesthetically is much better with blue where skin tones are concerned, yellow is a far better blend color for humans than purple).

Skin tones are particularly tricky with green screen as human skin tone (yes, I include all humans as this is 'hue' not 'luma' or saturation) is roughly where the upper 'I' excursion axis is on a vestorscope that would display the now rarely mentioned or used Y'IQ color model axes.

While blue is very nearly across the vectorscope from human skintone, green is about 90 degrees (and the angle of difference is less when green is lit warmly with tungsten) and therefore the direct spill suppression color is also close to 90 degrees...neither favoring skin tone/typical hair colors.

Therefore, unlike spill suppression using bluescreen, which nearly directly favors human skin and hair coloring, spill suppression against green has very little room for error between a green aura and a lavender one. Lighting the scene with daylight 'shifts' the green color 'bluer' which reduces it's similarity to skin tone, as opposed to 3200 tungsten which warms the green and adds a considerable amount of red, and since tungsten tends to be less full-spectrum anyway, subtracts other colors as well. Daylight sources may lean colder, but mos daylight sources emit a far more complete range of light spectrum across the gamut of visible light.

You can always 'warm up' your skin tones after the key is pulled, but reducing the amount of red in the image to try to grab a better key when lit with tungsten, which is primarily red, can make a good key AND a good image a real challenge.

For reference, I've got a vectorscope diagram here:

Tim_Kolb-Tech_Blog: vectorscope

As far as 10 bit acquisition is concerned, I think it's always a good idea for compositing. I used the KiPro unit for the greenscreen session I referred to earlier, but there is some question whether or not PC based QT will decode it as 10 bit, or 8 bit as the complaint seems to be that the PC version of QT is limited in it's ProRes decode abilities (I've not tested this myself, so I can't attest either way, but probably others here would know for sure). If you're going to a Mac for post, then I'd say to rent a KiPro and record 10 bit ProRes. It's far lighter and easier to work with than an entire computer system.

If you're headed to the PC, things aren't as streamlined. AJA Xena cards will record 10 bit, but you're back to bringing in a computer. There are several hardware routes to go to record to CineForm, which is arguably the best codec available on the PC...but you'll need CineForm's software to edit the material most efficiently. You could use a higher end VTR connected by SDI (HDcam SR or AVC Intra), but if you're on tape, you're stuck with RT ingest. Uncompressed is obviously great, but the hardware requirements are stiff...

Yes, I'd turn the detail off...but then that's what I'd recommend for shooting with an EX1 in any conditions (I am an EX1 owner and love the little camera BTW).

As far as anything else, I'd just say that even though you'll hear many who are adamant that a green screen be at a certain IEEE level on a waveform, I would counter that you need the green screen to be at a different level then you foreground. 60 IEEE is great level for your green screen, but if your foreground is at 60 IEEE to be properly exposed, then your greenscreen better be above that, or you're only using two of the three factors you have to create a difference for the keyer...hue and saturation are important of course, but luma is the third property that you can utilize to create that separation between the foreground and your key background.

Sorry for the manifesto...got started and couldn't stop myself.

Good luck with your shoot.
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Old February 16th, 2010, 05:36 PM   #3
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Thanks for the detailed reply Tim. Thatís exactly what I was after.

Quote:
Originally Posted by Tim Kolb View Post
OK...first, try to NOT have the cyc painted around the sides if you don't need that range of movement.
Well, it is already painted. The back wall is 25x15 feet high and the side walls, floor and ceiling extend for 14 feet. But we are planning to shoot most shots with the talent outside of this green box so the wall, floor and ceiling would only be there behind them for cover. For full figure shots I was planning to put a green screen cloth on the floor outside this green box so talent would not stand inside the box to minimize spill.

That way we could still have the flexibility of being able to shot from the sides and low and higher angles to a point without the problem of spill.

There may be some shots that may require talent to actually stand inside the box though but not planning to do it all inside. Sounds like a sound strategy?

But eventually we will need the range of movement for some dolly shots and other moving shots.

Quote:
Originally Posted by Tim Kolb View Post
For light, I prefer daylight sources for green screen for the following reasons:
Thanks. Great info.

I was just worried because most of the lighting we would be matching in the background plates would be electrical lighting since a lot of the background plates are night exteriors. I was worried about lighting the talent with daylight balanced light and having to color balance it back to tungsten color would introduce problems and artifacts. 98% of the shots would need to be corrected.

Also because of the nature of night exteriors lighting a lot of the talent lighting will have to be hard light. Do you see a problem with that, specially in a cyc?

You normally only see green screen done with nice soft lighting on the talent. Thatís easier and all but wonít work here.

Quote:
Originally Posted by Tim Kolb View Post
As far as 10 bit acquisition is concerned, I think it's always a good idea for compositing. I used the KiPro unit for the greenscreen session I referred to earlier, but there is some question whether or not PC based QT will decode it as 10 bit, or 8 bit as the complaint seems to be that the PC version of QT is limited in it's ProRes decode abilities (I've not tested this myself, so I can't attest either way, but probably others here would know for sure). If you're going to a Mac for post, then I'd say to rent a KiPro and record 10 bit ProRes. It's far lighter and easier to work with than an entire computer system.
Iím Mac based. All the post work will be done in Final Cut Studio including the grading. Only for compositing they were considering somebody who works with Fusion, which is Windows only. Hope that wonít be a problem since we are leaning towards capturing the 10bit 4:2:2 to Prores. Not sure how Windows applications handle prores as I never used it on Windows. But on Mac, unless going fully uncompressed, prores 4:4:4 seems to be the only or at least best option right? As good or better than cineform at least.

The Kipro is a good suggestion but they seem to want to capture it to a Mac Pro as they already have very capable workstations. So they want to get a blackmagic SDI card. Since we are in a studio and the shoot will be 2 weeks it makes no difference having an entire computer system or not I guess. In any case they want to use some of what they already have.

Quote:
Originally Posted by Tim Kolb View Post
Yes, I'd turn the detail off...but then that's what I'd recommend for shooting with an EX1 in any conditions (I am an EX1 owner and love the little camera BTW).
Yep, I love the EX1 as well. Have been shooting with one since it came out. Got mine early on and never looked back.

About detail, have you tried doing it with the detail set lower and a higher crispening and frequency to minimize where the detail is applied? This is normally how I shoot. But I never tested in on green screen.


Quote:
Originally Posted by Tim Kolb View Post
As far as anything else, I'd just say that even though you'll hear many who are adamant that a green screen be at a certain IEEE level on a waveform, I would counter that you need the green screen to be at a different level then you foreground. 60 IEEE is great level for your green screen, but if your foreground is at 60 IEEE to be properly exposed, then your greenscreen better be above that, or you're only using two of the three factors you have to create a difference for the keyer...hue and saturation are important of course, but luma is the third property that you can utilize to create that separation between the foreground and your key background.
I was recommend to get as much saturation as possible on the green screen and that for that, exposing it at 50% would be where it looks the most saturated. It seems that bumping saturation in the matrix can help to get a smoother key as well. But this is all stuff Iím finding while researching.


Quote:
Originally Posted by Tim Kolb View Post
Sorry for the manifesto...got started and couldn't stop myself.
Not at all Tim. It was great help. Thanks!
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Old February 16th, 2010, 11:50 PM   #4
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For the deep cove, you can use things like a sheet of bead board on each side to block excess green spill...

The green being maximum saturated would seem intuitively to be the best, but again, it's the difference from the foreground. On FX Guide they did some green screen tests some time back and found that in one case, the best key was pulled from a green background that was extremely bright...seemingly overexposed. It just has to be different than the foreground.

As far as color temp...you could try tungsten, but tungsten on the green wall will push the color toward red.

ProRes 4:4:4 is nice stuff for sure, but CineForm 4:4:4 has been verified to be superior to HDcamSR. CineForm is wavelet-based which does give it some advantage over a DCT codec. At any rate (I'm splitting hairs here), ProRes 4:4:4 will certainly key very well...in fact I'd guess HQ 4:2:2 would likely be fine for most applications.
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Old February 17th, 2010, 12:11 AM   #5
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I totally agree with daylight for the green screen. I think tungsten is not the way to go at all. I was just concerned with daylight on talent because it has to look like tungsten later. But if daylight is to be used on the green screen I don't think I should mix and use tungsten on the talent, so I guess it will be daylight for all.

Cineform is PC only right?

Any comments on the hard lighting when in a cyc?

Thanks Tim.
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Old February 17th, 2010, 02:26 AM   #6
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Michael...

I hard-light my talent a lot and it's never a problem. It's to simulate outdoor light and quite often it's a single, hard light with no reflectors. Here's a frame grab from one of the shoots.

I always try to set the green screen exposure to 50 IRE. If the green screen is too bright you risk green flare which can eat away fine details like hair.

As for full-length, I did that only once so far where we had to turn a full-grown man into a dwarf-sized "menehune" running up to someone's porch. I wish we had a bigger studio but the effect worked pretty good.

Some DP's will use partial sets. An excellent example can be seen at StudioDaily.com:

Shoot It on the Virtual Backlot | Studio Daily
Attached Thumbnails
"High-end" green screen shot with the EX1-cindy-lanai-lookout-2a.jpg  
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Old February 17th, 2010, 07:03 AM   #7
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I agree on the hard light...It should be fine,but I would pay specific attention to the shadows to make sure you're blocking as much green spill as possible. With a whole cove painted green, it will be coming from every angle but camera...

After you've pulled the key, you can color correct the daylight lit scene. You can typically be more aggressive to push daylight warmer than tungsten in the other direction...

CineForm is PC and Mac, but I've never used it on a Mac myself.
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Old February 17th, 2010, 07:37 AM   #8
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Quote:
Originally Posted by Michael Maier View Post
Any other tips and advice on shooting with the EX1 for green screen is greatly appreciated.
May seem a bit of a cop-out here, but this has been very useful to me:

Hollywood Camera Work - Visual Effects For Directors - Intensive Green Screen training, Matchmoving, Compositing, Motion Capture and more

Things like having large quantities of black drape available in your cyc studio, working out your best deal on cyc colour and the parallax markers colour, even silly things like having mic stands with post-it notes to help tracks. All of it really good stuff as one moves the game from simple static backgrounds to more complex work.

DVmattePro has been good to me for straightforward stuff, but as soon as we're getting into the bigger league, with reflections of the key to handle (chrome, shiny surfaces), you move outside an edit package and into nodal keying and lots of travelling mattes to crank out each shot.

The difficulty is in the balance of getting too much info which puts you off starting, and not getting enough info which subsequently prevents you from getting the shots which enable you to finish the project.

FWIW, shooting green screen interviews is what I do a lot of. I'm 'getting away with it', though as the EX1 picture from SxS does generate some noise in the shadows (exacerbated by my Picture Profile though). For more involved chromakey shoots, I'd go the NanoFlash route.

It's sad but true that my best results have come from using Kinoflo Divas, with the cyc lit by 2ks off polystyrene. Far cry from my usual chromakey setup of a couple of Lowel Totas. The important thing here was that the 2Ks weren't dimmed, they just did their thing. The Divas had their special dimming thing. So we avoid the orange issue, which maybe why many folk like going daylight CT.

Hard lighting requires a LOT of separation and spill suppression from cyc to talent if you want dark shadows. Hence the need for black drapes.

I used to use the Chromaflex/Reflecmedia system where the entire backdrop lighting was taken care of by a simple ring of LEDs. It enables talent to be close to rear backdrop, but I stopped using it because it needs more space from talent to lens than I can usually provide. The LED ring ends up as a ring light. The backdrop works like scotchlite, but is expensive and must be kept clean - not good for floor cloth. I've since stuck to ordinary green felt and green paint.
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Old February 17th, 2010, 08:59 AM   #9
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Quote:
Originally Posted by Tim Kolb View Post

CineForm is PC and Mac, but I've never used it on a Mac myself.
I should add that the last I knew, BlackMagic could not ingest to CineForm, AJA was the hardware they interfaced with...

I know BlackMagic has some codecs of their own, but I'm far more familiar with AJA's products, so others would be of more help navigating the options on the BlackMagic Design side of things...
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Old February 17th, 2010, 12:55 PM   #10
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Quote:
Originally Posted by Tim Kolb View Post
I agree on the hard light...It should be fine,but I would pay specific attention to the shadows to make sure you're blocking as much green spill as possible. With a whole cove painted green, it will be coming from every angle but camera...
Tim's got a point. When shooting subjects that require "negative fill" and a hard shadow, any kind of spill can be a problem. While software can counteract green spill, just the fact that some kind of light is hitting a particular area could be a problem.
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Old February 17th, 2010, 05:12 PM   #11
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Thanks guys! A lot of great info there.

Dean, thatís a great looking key! Very nice.
Using partial sets would be great, specially when it comes to floors but I donít think they are going for that or even have the budget.

Guys, what about matchmove? Have any of you an experience with matchmoving EX1 footage?

About the detail, Iím still a bit unsure to totally turn it off. I normally find it too soft with it off, but I know it will help the key. But if itís too soft in the end, specially given normally keying can soften the footage, I will have a whole show to sharpen in post which will be a pain. I donít know.


The deal with hard lighting is that it produces hard shadows. I think one of the reasons people shoot with very soft lighting in a cyc is because you wonít have hard or any strong shadows falling on the green walls. Thatís what I was concerned about in a cyc and I was wondering how to approach that?

What about back light? I have heard that hard back lighting can make keying more difficult because the edges are very crispy. But we will certainly need hard back light to match some shots.

The dark shadows under hard lighting is why I was asking about gamma use. Some gammas are just more noise than others.


Quote:
Originally Posted by Matt Daviss View Post

Hard lighting requires a LOT of separation and spill suppression from cyc to talent if you want dark shadows. Hence the need for black drapes.
Quote:
Originally Posted by Tim Kolb View Post
I agree on the hard light...It should be fine,but I would pay specific attention to the shadows to make sure you're blocking as much green spill as possible. With a whole cove painted green, it will be coming from every angle but camera....
Quote:
Originally Posted by Dean Sensui View Post
Tim's got a point. When shooting subjects that require "negative fill" and a hard shadow, any kind of spill can be a problem. While software can counteract green spill, just the fact that some kind of light is hitting a particular area could be a problem.
Yeah, I hear you. The problem is that when using the whole cyc you canít have any black drape so how to control spill and get separation then?

Thanks again guys.
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