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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Problem with greenscreen Footage "Ringing"

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Daniel Broadway

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Hey guys. I'm working on a greenscreen shot. I'm getting a ring around my edge when I key. I didn't add sharpening out of REDCINE, as I know that can wreak havoc on keys. This was shot at 4k, and exported out of REDCINE at 2K.

Keyed with Keylight. If you look at the blue channel, you can see ringing or edge enhancement looking artifacts there. A little in the red channel too. What could be causing this? I am applying no sharpening, so I don't know where these artifacts could come from. I do know the shot was filmed through phone booth glass, as the man is standing in a phone book, but would that bend the light in some weird way to create this problem?

Used the latest REDCINE build, Linear scaling. I even exported to 4K with the same problem.

red_key_02.jpg


Any advice or help would be most welcome. :)
 
Maybe you are loosing sharpness through the prop glass as it is not optical glass. Just a guess. Can you simply choke into the mask a bit to hide the issue?
 
Did you use any OLPF compensation? AFAIK, that is sharpening.

What resize algorithm did you use, as some of them can create ringing artifacts.

What compositing program are you using?

I would try exporting at 4k and turning off any OLPF compensation, see if either of those help.
 
Charles Angus said:
Did you use any OLPF compensation? AFAIK, that is sharpening.

What resize algorithm did you use, as some of them can create ringing artifacts.

What compositing program are you using?

I would try exporting at 4k and turning off any OLPF compensation, see if either of those help.
Click to expand...

Linear scaling. I even exported to 4K with the same problem. :( I'm using Adobe After Effects and Keylight.

I set detail in REDCINE under OLPF to "Low, Medium, and High" still didn't help. You can't add sharpening to RED footage while shooting, right? I thought that was all done in post.
 
I'd need an R3D to look at. That would help me help you.

Graeme
 
I'm getting the exact same thing in Nuke 5.2 using primatte.

I'll have to check the olpf settings in the nuke decode node and do some testing. That fringe is a beast to remove! Try to make it transparent or supress and it crawls into the flesh tones.

It does seem to be most apparent on red clothing against the green.

Build 20.
 
I am running into this problem again with some RED material shot on RED One with the MX sensor. Anyone ever figure out what's causing this?
 
I'd export out at 4k, comp, then scale down to 2k afterwards. Even the best downsampling filters will make for a small amount of ringing.

Graeme
 
Graeme Nattress said:
I'd export out at 4k, comp, then scale down to 2k afterwards. Even the best downsampling filters will make for a small amount of ringing.

Graeme
Click to expand...

I was comping at 4K, and still have the problem. I wonder if it's some sort of chromatic aberration of the lens. Hmmm.
 
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.
 
Daniel Broadway said:
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.
Click to expand...

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
 
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?
 
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.
 
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