Blue and Green screen experiments

Jim Arthurs

Jim Arthurs

Well-known member
Hi all... did some tests yesterday and fiddled around a bit today with the footage. First, new info from so many folks coming in on the best settings for color, detail, noise, etc. make shooting yesterday like shooting an eternity ago.

I shot some blue and green screen with -4 detail, and it wasn't enough to wash away some pretty obvious edge enhancements with the keys. So, will try -6 or -7 next time, and mess with vertical detail as well.

Gamma was black press, and I got in trouble shooting -6db with low knee setting on one test... I ran out of top end on the exposure and skin tones saturated very quickly with an ugly flat look. 0db and high knee made the skin look much better, and overall I've not seen any real noise value to shooting with the -db's in general.

Tungsten lighting seems to work fine for both green and bluescreen, as indicated in the noise floor tests I did a few days ago. I really like +2 chroma, and not just for key work... it's so bright and happy, but not overly saturated. You can easily pull it out in post vrs adding chroma in post, and if you record with a 4:2:2 recorder you certainly won't have problems dealing with extra chroma.

I've been shooting with the 14-140, but REALLY like my old Nikkor 20mm and 50mm AIS lenses... shooting a digital key with the 50mm yesterday was the first time I used that lens since shooting a 35mm Mitchell FILM blue screen shoot a decade ago with that same lens. Talk about re-gifting.

I made up some layered Photoshop files with grabs from both blue and green screen foregrounds, using the on-board AVCHD, nanoFlash 100Mb/long-gop, and nanoFlash 280mb i-frame so you can channel and pixel peep the various differences. The blue channel is where all the interesting stuff is going on.

http://ftp.datausa.com/imageshoppe/outgoing/AF100/CHROMA_AVCHD_nano100_nano280.zip

In addition, here's a green screen comp test (over medium grey) using nano at 280Mb/sec. Yep, still too much edge-enhancement... well, it IS a test, afterall.

http://ftp.datausa.com/imageshoppe/outgoing/AF100/nano280_green_screen_h264.mov

Much to learn in general, hopefully will have a chance to do some real photography soon...

Regards,
 
Was about to go to bed when I found your post - had to fire up Shake and take a look. AVCHD did better than I thought it could - although that doesn't take away its awful jaggies and lack of detail - especially under the rabbit's ear and in dealing with the hair along your forearm.
Still, for web work it'd probably be OK.
The Nano280 was so much easier to control. Of course, these are just stills, so hard to judge noise. In your QT there's a lot of buzzing around the crystal bowl, and it seemed the hair on your arm was a little too dense, so with moving footage, may have been more difficult to pull off.
Still - it looks and plays great! Thanks for the samples, and if you have some moving samples you can throw out here, it would be awesome to play with some of that as well.
Thanks!
 
Definitely like the video test. That key is very acceptable and useable in my opinion. Would really like to see some greenscreen stuff with the native codec to compare ( in motion ). Using the bubble wrap and transparent items is very clever and wow, it really produced...
 
Very nice work Jim. Thank you for sharing. AVCHD does seem to hold up well!

Would you recommend shooting -6 or -7 detail for shooting in general?
 
Thanks guys, the noise is generally in areas that have had color spill suppressed out of them, but overall wasn't too bad.

One thing I didn't test was how the AF100 would handle dealing with shadows on the chroma surface, like a painted cyc with the talent walking on it. I'm curious to see how the noise performs in the screen area shadow detail you are trying to preserve.

I'll have to come up with somehow to share the files other than my private ftp... the native AVCHD aren't a problem, but the nano clips are all on the large size.

Sorry the subject matter wasn't a pretty girl. You can't always get those when you need them.

Yes, the AVCHD performs well. I like the AVCHD and no question it works better than 35Mb/sec EX codec. Of course the extra chroma detail of the nano is important when you start to push the mattes around on anything but the "conditions perfect, one button key", but in both cases (4:2:0 and 4:2:2) you should add a bit of chroma blurring before the key. In the case of 4:2:0 that is an equal amount of horizontal and vertical blur, in 4:2:0 you just need to add horizontal blur). Back in the early days of film digital, even 4:2:2 was considered a chroma weak bastard format, when compared to good cineon film scans.

Anyway, I hope to shoot some more material with detail at -7 in all cases, chroma and normal footage. With the EX1 you can just completely turn detail off (not messing with any of the sub-settings) and rest assured the image isn't missing any actual real resolution. With the HVX200 I felt the lowest setting was truly robbing the camera of a bit of its overall true sharpness. With the AF100, I still don't know.

I do know that -4 will still give you quite a bit of edge enhancement that you can't get rid of when pulling the key, except by trimming in on the matte, and you don't want to do that. So GO LOWER than -4 when keying, okay?
 
Your choice of subjects for the greenscreen test was better than a "pretty girl." I loved the inclusion of bubble wrap and crystal/glass. And noise level on preserved shadows would be a great test. Along with some mismanaged lighting on the backdrop - make it more "real world" heh heh. Thanks much, and as for sharing files, can you use those online file serving solutions? I think they're free . . . just saying :)
 
Great test (and excellent key) I am so pleased you took the trouble and did it.

I was really worried about keying from this codec because I do a lot of them. I am a lot less anxious about that aspect now.

Thanx
 
Okay, here's another example, this one a bit more demanding on the noise floor and codec combination....

http://ftp.datausa.com/imageshoppe/outgoing/AF100/BUNNY.jpg

Here we have floor contact and the desire/hope to retain the shadows on the green screen as much as possible. Tungsten lighting, -7 on detail/vertical detail (anything higher seems to leave traces of edge enhancement). The framed area is surrounded by white bounce cards to counter-act as much spill as can be hoped for.

Here is a zip with layered Photoshop file of a frame (AVCHD, nano100, nano280) and the raw AVCHD video file...

http://ftp.datausa.com/imageshoppe/outgoing/AF100/BUNNY_AVCHD_nano100_nano280.zip

And here is the raw nano file (as .mov)

http://ftp.datausa.com/imageshoppe/outgoing/AF100/Bunny_nano100Mb_longGOP.zip

If you're on the PC, you can download a file conversion tool from the Convergent Design website to re-wrap the .MOV to .MXF. I always shoot .MOV because of that easy transcoding ability, even though I work and edit mostly on the PC.

I haven't spent any real time working the key, but wanted to put these out there. I do see a lot of noise in the bunny's shadows when trying to retain them, along with a larger, random dancing mottling like effect.

Regards,
 
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