problematic green screen with XAVC-S

Mindmatter wrote on 11/3/2015, 8:00 AM

Hi all,
just working on my first green screen project I did recently, with talking kids sitting in front of a green screen, recorded in XAVC-S 50mb/sec on my Sony A7S.
While it seems I can key the thing quite reasonably apart from the typical hair problems, there's a lot of artefacts around the contours, looking like the typically jagged lines of a low res jpeg. It seems V13 has a hard time with the smooth details of clothing, no matter how much I tweak the chromakey parameters in vegas.
The lighting seemed correct, the screen was well lit, there were soft boxes for the faces, and a back lighting for the hair contours.
The thing is, I've seen far better green screen keying on youtube tutorials with the same cam settings, and lesser quality lighting, at least they all didn't have the jagged lines issue.
Could someone point me to what I'm possibly missing here? Is it possibly codec related?
Thanks!

Comments

OldSmoke wrote on 11/3/2015, 9:04 AM

Are you working in 8bit or 32bit full range? Did you record HD or 4K?

Mindmatter wrote on 11/4/2015, 5:13 AM

Thanks Old Smoke,
I recorded full HD , the A7S records in 4.2.0. at 8bit, XAVC-S at 50mbit/s
The Vegas project is set to 8 bit, I just exprerimented with the 32 bit settings, it does not really get any better, the contours are still heavily jagged / pixelated.

OldSmoke wrote on 11/4/2015, 5:41 AM

Can you post a screen shot and maybe upload a frame of the video on dropbox or similar for others to have a go at it?

Mindmatter wrote on 11/4/2015, 8:10 AM

Here you go:
( for some reason I can't seem to make the link active, so you'll have to copy paste it into the browser )

OldSmoke wrote on 11/4/2015, 8:40 AM

Just remove the "s" from https changing it to http.

OldSmoke wrote on 11/4/2015, 8:44 AM

I looked at the two images. Are you sure that this is what comes from the camera? Do you have a short clip straight from the camera? Have never seen such bad edges even with my lesser HD cameras. is your preview Best/Full?

Edit: Try converting the clip with the free Catalyst browse to XAVC-Intra HD and see if that helps.

VMP wrote on 11/4/2015, 8:46 AM

Using the chroma blur plugin before the Chromakey plugin helps occasionallyc
Also there is a blur slider in the .default Chromakey plugin which you can try.
But these are quite jagged indeed. Looks like the footage source settings are off, similar to interlacing.

VMP

rs170a wrote on 11/4/2015, 8:46 AM

Give Fusion from Blackmagic Design a try. It has a learning curve but the chroma keyer in it is far better than the one in Vegas. Did I mention that it's free :)

p.s. an unaltered image (i.e. sitting in front of the green screen) would be best for us to play with.

Mike

Mindmatter wrote on 11/4/2015, 9:07 AM

Thanks everyone so far!
Yes indeed, it's the worst keying I've ever seen...

I've changed the snapshots, as the first 2 were not at best/full, but it doesn't make much difference.

here's a 10 sec video straight from the cam, shot during the lighting setup, so it's not quite lit the same, but the problems in V13 are identical:

https://www.dropbox.com/s/gq98lj9b2651o1y/C0001.MP4?dl=0

it looks very soft, as I always turn down the detail / sharpening in the cam and sharpen in post.

If it helps, the A7S was set to cine 4 picture profile and cinema color space.

My only possible explanation so far is that I may have messed with the shutter speed, as I was switching from photo to video all the time. Could that be the cause? I need to check if I can find the video metadata somewhere.

GregFlowers wrote on 11/4/2015, 12:30 PM

The technique I do with almost all my greenscreen footage that works well for me is as follows. I first apply the "saturate green" from the secondary color corrector to really even up the greenscreen and make it pop out. I then apply a garbage matte around the subject to eliminate as much excess greenscreen as possible. I apply the chroma keyer and tweek to my liking. Finally I apply a final color correction to my subject. I've been using this workflow for a while and it works pretty well.

By the way the best greenscreen material I've ever used is fluorescent green spandex fabric. It requires minimal extra lighting. It lights really evenly and pops out on its own. Wrinkles can be easily stretched out.

These days I use the Boris plugin with light wrap for best results.

farss wrote on 11/4/2015, 12:46 PM

[I]"I recorded full HD , the A7S records in 4.2.0. at 8bit, XAVC-S at 50mbit/s"[/I]

The 4.2.0 chroma sampling is not helping. For chroma keying 4.2.2 will help a lot.

Bob.

GregFlowers wrote on 11/4/2015, 1:00 PM

Original PNG http://www.dropbox.com/s/ch3aqn6ib1d268p/original.png?dl=0

After masking http://www.dropbox.com/s/qipb2p1psmwjppq/mask%20added.png?dl=0

Green saturated http://www.dropbox.com/s/t6m6h94ww3ihyqa/saturate%20green.png?dl=0

Chroma keyed http://www.dropbox.com/s/ezj0eyi4iqkoew8/chroma%20keyed.png?dl=0

Color corrected http://www.dropbox.com/s/f7dx1nhxngmlcdo/color%20corrected.png?dl=0

Final video http://www.dropbox.com/s/ibskeb1yipmtem1/green.MP4?dl=0

Mindmatter wrote on 11/4/2015, 1:17 PM

Thanks for the input everyone!

Thanks so much for taking the time to do this and sharing your workflow, Greg Flowers!
It does look much much better than my result, I'll give it a try tomorrow.

Bob, you're right about the 4.2.2., but in this case, I've seen much better keying from far worse cameras. It doesn't seem like your typical keying / fringe etc issue, it looks different, someone mentioned it looked like an interlace problem, although it obviously isn't. Besides, I don't own a 4.2.2. cam at the moment...
I've checked greenscreen clips done with the A7S on youtube, they were very clean.

OldSmoke wrote on 11/4/2015, 3:14 PM

I wonder if those "clean" green screen videos on YT are done with an external recorder, the A7S does output 422 via HDMI.

Former user wrote on 11/4/2015, 4:52 PM

Here's a drop and play preset using HitFilm 2 Express (just a static frame)... Looks pretty good to me :-)

Chroma Key Sample