Problem with greenscreen Footage "Ringing"

[Deanan]

I was comping at 4K, and still have the problem. I wonder if it's some sort of chromatic aberration of the lens. Hmmm.

can you email us a r3d still frame?

[Daniel Broadway]

Ok, I did a little more experimentation with this. I believe I have figured out the cause of it. It appears the artifact can be introduced one of two ways.

1.) Using OLPF Compensation of any kind will produce this artifact.

2.) The main culprit of what was happening when I was trying this, is that I was raising the saturation of the greenscreen footage to 1.5 or 2.0, and this will also make the "ringing" show up. However, the raw footage is so flat, it was necessary to raise the saturation above 1.0 in order to get a clean separation in the RGB channels. The higher the saturation, the lower the values in the RED and BLUE channels as opposed to green, thus giving me more color difference to be able to pull a key.

I don't know much of a way around this, because raising the saturation really gives you nice color separation in channels, but also adds ringing artifacts.

[Hans von Sonntag]

However, the raw footage is so flat, it was necessary to raise the saturation above 1.0 in order to get a clean separation in the RGB channels. The higher the saturation, the lower the values in the RED and BLUE channels as opposed to green, thus giving me more color difference to be able to pull a key.

I humbly disagree. "Preparing" footage for keying is rarely beneficial. Only if DV-compression blocks or bad noise contaminates the footage blurring the blue channel may help a bit.

It has always been the best way not to manipulate footage PRIOR the keying process. In the old film days you never pushed saturation or anything else in the telecine process that may introduce noise and other video artifacts to footage. Such green screen scans looked very flat, often with a distinct orange tint. Pulling a key off such flat scans was much, much better than off saturated "right" looking footage.

There is a reason why Red supplies RedlogFilm. For pulling keys we use RedColor2 or Camera RGB (the latter one has a slight more magenta tint) and RedlogFilm. No OLPF compensation, no sharpening, no raised saturation, no curves, nothing. We mainly use MasterPrimes or sometimes SuperSpeeds, the old M sensor and daylight light. But I also once achieved very good results with a Cook 18-100 and tungsten lighting. File format after debayering is DPX. We use Autodesk's Modular Keyer but the offerings by The Foundry will do it adequately well.

IMHO, Red footage ist particular good for keying.


Hans

[Daniel Broadway]

I'm sorry to keep bumping this thread, but I am again running into this problem, and I am at a loss to fix it. It has become highly frustrating at this point. I am trying to key a 4K greenscreen plate, and each individual hair keys beautifully, but when I spill suppress, it leaves nasty ringing artifacts and discoloration. I imported the R3D directly into NUKE, and in the Red and Blue channels, there is definitely some ringing artifacts heavily around the hair, even before keying. They are very pronounced. The artifacts look EXACTLY like edge enhancement artifacts from prosumer camcorders, so I am thinking some kind of Unsharp Mask type effect is going on somewhere in the pipe.

I am not using OLPF compensation, or any sharping of any kind. I'm not scaling anything. I have now experienced this problem with two Red One cameras, and can't believe I'm the only one. However, I am having a very hard time finding anyone else that's posted about. I am at a loss, but desperate to fix it. Is there anyone here that could shed anymore light on this?

[Tony Lorentzen]

I have successfully exported 1080p ProRes files many times and keyed from them without any problem whatsoever. These days I'm mostly working with the R3Ds directly in Premiere and After Effects since I ditched Final Cut about 4 months ago when I bought the CS5.5 Production Pack. If you could upload a single frame R3D would be required if you want some help.