record settings for greenscreen

E

editatjoes

Active member
I've searched the forums and read up on recommended scene files for greenscreen, but didn't find anything about record settings.

I'll be shooting tomorrow with a very experienced crew, so the lighting and other production details should go smoothly.

Here are the choices I'm not sure about:

Video Cam or Film Cam?

720 24pn or 720 30pn?

leave the shutter alone or adjust shutter angle (synchro scan) to 90 instead of 180?
(this is something I've had DPs do when shooting film to eliminate motion blur with greenscreen shots)

Unfortunately I don't have time to run tests, so I appreciate any help from those who've done this before.

Thanks-
 
More or less blur is not an issue if the screen is uniform and the talent/subject properly lit to reduce spill.

Remember, shooting a subject against blue or green is in essence shooting the subject against black velvet from the point of view of the compositing software. To your eye, the bounce from the green screen or blue screen seems like fill light, but it is not. You MUST add additional white light to the edges of your subject to counter-act the spill. Failure to do this will result in darker areas of your subject "buzzing" with noise when spill reduction removes the color cast. This is not HVX specific, but is an issue with all formats and cameras.

I would recommend shooting 1080p for your key backgrounds unless you need slow-motion, the extra bandwidth and slight horizontal resolution increase per frame will help make your shot a success. 1080 foregrounds work well over 720p backgrounds.

Here's some specific HVX/blue screen tests I did a while back...

http://www.imageshoppe.com/HVX_bluescreen2.html

Regards and good luck!

Jim Arthurs
 
Jim,
Great examples and explanation! How did you pull the key? I don't know Edius, so was wondering if there was another plug-in/software used. Thanks for the excellent webpage.
 
Yes, nice webpage. Thanks Jim.

Editatjoes, I wonder if 720p would be better than 1080i for the motion blur problem? I'm wondering if interlacing creates a problem.

My last greenscreen was film cam, 1080, and I had the shutter at 180. I had real problems with any faster-than-talking-head movement.
 
These appear to be a good starting point for HVX Scene settings when shooting greenscreen. (According to previous threads I've read from Jim and Barry).

CineV
Detail -3
Chroma +2
Master ped -2
Matrix normal
 
Hi Bob, just used the Keylight plugin that comes in After Effects. I only used the trial of Edius to display waveform/vectorscopes of the signal.

I dislike interlaced footage for keys, but remember, you're storing 1080 24p/30p in an interlaced stream, the individual frames are true progressive. Trust me that shooting 1080 (or DVCPRO 50) will give you an edge (pun intended) over the same shot in 720p.

As to motion blur... it's really no problem as long as your background is very uniform and lit to proper levels... too dark and you'll expose the DVCPRO compression when you bring up the levels, too bright and you'll loose your ability to resolve details. You want to aim for the levels I mention on the web page link I gave you. There are sample movies there that I did with fairly extreme head motion, and if you frame-by-frame you'll see that everything resolves properly.

Regards,

Jim Arthurs
 
Just for reference, I followed Jim's advice and then did my own tests on both the PC in Premiere 2.0 (via Raylight) and After Effects 6.5 and on the Mac in FCP 5.04, After Effects 6.5, and Shake 4.1, and Motion 2.0 in both 720p24pN and 1080i/24pA.

720 vs 1080
The first thing that I need to report to you is that side-by-side comparrison and then using overlay of stills in photoshop with difference blend mode to compare, I found that the 1080 footage was sharper then the 720 footage. I would describe the difference this way: In a CU shot of an actor "fluffing" her hair, both the 720 and the 1080 composited just fine onto a background. But in the 720 shot the hair was blurred and lacked detail, and in the 1080 shot you could see individual hairs. And when I reduced the 1080 frame to 720 and compared, there was still a noticeable difference in the detail.

Best Key and Composite?
The results were clear. The key filters in Premiere and in Final Cut were adequate but left edge artifacts which would have required chokers and spill supressors and a lot more tinkering than I wanted to do. The Primatte keyer in Motion worked about the same. Getting to After Effects and to Keylight on both the Mac and the PC made a huge difference. Basically, I could drop Keylight onto the footage in 720 or 1080 and the background disappeared as soon as I used the eyedropper. I maybe moved the screen strength or the bias slider to improve the key a bit, but nothing more was required. There was no difference between using Keylight on AE on the PC and Keylight on AE on the Mac -- they worked identically. Now Shake, with its 32-bit Keylight, blew everything else away. In one test composite I had an actor wearing a light blue-green color that was similar in luminance to the screen and picked up a lot of green spill light. And in AE/Keylight I was fighting with the settings to avoid transparency and the background showing through. Shake/Keylight-32 differentiated the color perfectly and transparency was no problem. Side-by-side comparrison of the same item at 720 composited in AE/Keylight and in Shake/Keylight-32 showed that there were some color artifacts or transparency artifacts that sort of lightened the image slightly or washed high-frequency detail out slightly, and it was easier to tell it was a composite. The Shake/Keylight-32 version looked solid and blended into the background so that it was much harder to tell it was composited. I didn't try the Primatte-32 keyer in Shake or any multi-key techniiques.

Ranking: (1) Shake/Keylight-32, (2) After Effects/Keylight (PC or Mac) (3) FCP, (4) Motion/Primatte, (5) Premiere

Workflow
Getting the 1080 pulldown removed on the PC was easy -- Raylight just did it.
Getting the 1080 pulldown removed on the Mac was easy with AE, because it would remove the pulldown correctly with its "interpret footage" feature. But the path to Shake in 1080p is treacherous.

I've now learned that CinemaTools 5.1.1 is the way to do this, and I'm waiting for the cross-grade to arrive. I did find a way to get 1080 with pulldown correctly removed to Shake in the 5.0.1 FC Studio tools, but it required several tricks and maybe 30 expirements to find something that worked. The path is far from obvious and not a very practical workflow.

At the moment I would say that for quick keys and for keys where quality isn't and issue, I would go with 720p and the FCP keyer. For most things I would be happy with 720p or 1080p in AE/Keylight. And for film-quality work, I would definitely go with 1080 to Shake with Keylight-32, and then reduce on output to 720 in Shake.

The difference between a 720 Shake key and a 1080 Shake key when reduced to 480i/DV ? -- I could see it. But I knew what to look for.

Andy
 
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