Green screen problem

L

Lenilenapi

Carbonite Member
I shot a green screen interview last week with the HVX and just got a call from the producer complaining that the shot was noisy and that made the key difficult to cut. The issue was the hair which on this guy was very frizzy.

I believe the lighting was fine. I have been doing this many years and have shot many keys.
The key was even at about 45 IRE and the backlights seemed right with a little warmth for separation.
Exposure was fine on the subject.


I shot the camera @ 1080i/30P with the Detail at 0 and Coring at 0 using HD Normal and CineMatrix probably at 0 though I'm not sure - maybe + 1.

Any ideas about this?

I thought about dropping detail a few points and bringing it up in post, but neither the client nor me wanted to experiment. Another thought was to perhaps make the green screen brighter.
 
It's kind of hard to tell unless I see a sample. I've been shooting green screen with this camera and have found very good results by lowering the detail to the lowest setting. Doing this not only reduces the noise, but also shrinks the annoying black outline which detail enhancement always seems to add to a blue or greenscreen shot.

Frizzy hair is notoriously difficult to key in the best of circumstances. I think it's more likely the resolving power of the HVX and the DVCProHD codec that's going to cause the most problem in gettng that frizzy hair to key.
 
So you are lowering the detail all the way to - 7?

Do you raise it again in post.

Are you shooting 1080?

What about the screen IRE level, is that an issue?

Thanks KC.

- Lenny
 
Lenilenapi said:
So you are lowering the detail all the way to - 7?

Do you raise it again in post.

Are you shooting 1080?

What about the screen IRE level, is that an issue?

Thanks KC.

- Lenny
Click to expand...

Yeah, I lowered the detail to -7. No, I didn't bring it up in post, I guess you could, if you were so inclidned, but you'd also be introducing a lot of noise. And yes, I did shoot in 1080/30P. It sounds like you were shooting a head and shoulders shot and the lowering of detail, at least IMHO, is not as noticable on the human face - it can even be complimentary - softening out facial imperfections.

I didn't really worry about the IRE level of the green screen, although, looking at something I just shot - the greenscreen came out around 45IRE, anyway - go figure.
 
The best advice I can give on the noise issue is to put the green screen IRE at 60-65, in the work I've done it's controlled the noise in subject/screen transition areas better than screens exposed at a lower level. Much better.

Here's a still where I practice what I preach... forgive the uneven level and weak chroma (client provided green paper backing).

http://ftp.datausa.com/imageshoppe/outgoing/HVX_TESTS/STILLS/65_IRE_GRNSCRN.png

And here's a short test key... notice that the hair is still finely represented, and as noise-free as this camera can produce...

http://ftp.datausa.com/imageshoppe/outgoing/HVX_TESTS/65_IRE_KEY.mov

Footage was 1080 30p resized to 720p with horizontal blurring on Red and Green channels before pulling matte, final comp was SD. Detail level was -3 which I find as the sweet spot for this sort of work, HD Normal gamma which seems to work as well as Black Press for me.
 
Oh my, Arthurs. That key is amazing.

Forgive my ignorance: how do you put the greenscreen at 60-65 IRE? Can you give us all of your settings?

This key is the cleanest I might've ever seen from the HVX, even if it's just an orange background.
 
Thanks Kholi... in this case the bulk of light was coming through an overhead 12' by 12' silk we rigged... then the talent placed and cross-rimmed by 1K's to kill spill. With a couple softbox in the front filling both talent and screen. Levels were adjusted by the soft sources hitting the screen. The setup had to work with head to toe shots as well. I used HD Rack to record, checking the keyability in AE as we shot so there would be no surprises later.

I used an orange BG to A.) keep the file size of the .mov small for downloading and B.) a solid color shows off any issues with the matte easier than an actual background.

I've had better keys with the HVX (see the link below) than this, but it was adequate for the job, which was a virtual set in the Serious Magic style (but completely custom built and done in a 3D package to provide the moves.)

In any event, keeping the HVX noise in transition areas under control is a function of higher levels on the screen.

The danger is to go too high... if the green channel clips full saturation then the other two start to slide up towards white... which causes a lime/cyan fringe color that can't easily be removed by spill controls...

Finally, I'm leaning toward HVX recorded 1080 as superior to DVCPRO 50. Yes, DVCPRO 50 is less-compressed, but it seems to have more noise than the HD formats... let me put that differently, for some reason, the noise "grain" in DVCPRO 50 is the same size as the noise in HD (you'd expect DVCPRO 50 noise to be "scaled" along with the image, reducing it's effect).

http://www.imageshoppe.com/HVX_bluescreen2.html
 
Wow man. Just, wow. Those links look natural as hell. Thanks for sharing that!!! I knew that 1080 was the format to do this kinda work in, but geez... I really didn't think you could pull such stellar keys with the noise factor.


I am going to be doing some intense greenscreen work in the next two weeks for a short and this is stuff I have to know. Thanks for taking the time out to field questions.
Edit: Just read and re-read the article. Man. Those keys were so natural I would've NEVER guessed they were in front of a bluescreen. Simply amazing man.

So basically, it really only comes down to getting a pure green or pure blue, one that's very bright and ultra saturated and as well, evenly lit. What about your keying process? What do you use? Any extra tricks of the trade on this?
 
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Kholi said:
So basically, it really only comes down to getting a pure green or pure blue, one that's very bright and ultra saturated and as well, evenly lit. What about your keying process? What do you use? Any extra tricks of the trade on this?
Click to expand...

That's pretty much it... the proper luma and chroma and a flat even lighting for the best work. The luma is just the level and easy to adjust if the subject and screen aren't being lit by the same source, the chroma is harder to get right unless you have high quality paint/fabric. The goal is to not over-saturate the key channel, yet get it as saturated as possible. 60-65 IRE does that with green, 35-40 IRE does that with blue.

The keys themselves were pulled with Keylight in AE using pretty standard settings. I do blur the red and blue channels before pulling the keys on the horizontal, depending on the codec used to decode to RGB. The green screen subject I also did a roto matte to take out the outside edges of my poorly lit screen, but nothing complicated or animated.

What I'd like to do is a step through the various illumination levels to show objectively that the edges are better with the higher values... maybe if I have time this weekend... it's time to re-do the web link with all the things I've learned since back in May and consolidate all the various codec quirks into one reference.
 
Arthurs...that information is so useful and those Keys are indeed amazing!!!! Thank you for sharing all this with the rest of us!
 
Jim Arthurs said:
That's pretty much it... the proper luma and chroma and a flat even lighting for the best work. The luma is just the level and easy to adjust if the subject and screen aren't being lit by the same source, the chroma is harder to get right unless you have high quality paint/fabric. The goal is to not over-saturate the key channel, yet get it as saturated as possible. 60-65 IRE does that with green, 35-40 IRE does that with blue.

The keys themselves were pulled with Keylight in AE using pretty standard settings. I do blur the red and blue channels before pulling the keys on the horizontal, depending on the codec used to decode to RGB. The green screen subject I also did a roto matte to take out the outside edges of my poorly lit screen, but nothing complicated or animated.

What I'd like to do is a step through the various illumination levels to show objectively that the edges are better with the higher values... maybe if I have time this weekend... it's time to re-do the web link with all the things I've learned since back in May and consolidate all the various codec quirks into one reference.
Click to expand...

Wow if you have time to do that, it'd be awesome. I already Bookmarked your link and set it at the top of my HVX links.

This info has been killer.
 
Go Ahead Jim,

i guess you are one of the most experienced users with green/bluescreen her, so this is and will be a great help...shows me that i definitly have to start some tests finally..!

The codec question would be very interesting, specially which one you use when exporting from AE.
I do work with Edius(probably should try to key there first hand..) and Canopus HQ and lossless...great codec until i export something from AE in Canopus codec..havent found out yet why..by wpuld be curious to know how you handle the Codec-issue..!?

Enjoy your weekend-and make us enjoy your report..!
 
I've never pulled a green screen, so I don't know what's possible. But it seems to me that there's a narrow green border around the girl's shoulders. Also some slight green spill in the hair. Maybe none of this is noticeable when you put in the intended background (instead of orange)?

I don't mean this as criticism. I'm going to start doing green screen soon, and I want to learn as much as I can from people who are already doing it well.
 
No problem... there is certainly more that can be done with the composite, and slapping it over a single garish color is the nastiest thing you can do to a comp... this was more an example of how to prevent noise and edge chewing that happens with green screens illuminated to too low of a level.
 
Jim,

I really don't understand why you blur the red / blue channels (DV compression) if you can record in DVCPRO 50 at 4:2:2 color with the double information for blue and red ?
Your key is good, but i can see some DV compression artifacts (blocky) that should be avoided with 4:2:2.
The blue screen article you posted was using 1080 uncompressed, it was recorded direct in Velocity system without the DV compression, which should be better of course.

Ulisses
 
ulisses said:
really don't understand why you blur the red / blue channels (DV compression) if you can record in DVCPRO 50 at 4:2:2 color with the double information for blue and red ?
Click to expand...
Hi Ulisses... people were horizontally blurring 4:2:2 years before DV 4:1:1 came on the scene. Yes, it has double the color information as 4:1:1, but yet only half the rez of the luma and can benefit from this technique.

Secondly, there are various ways the existing codecs interpret DVCPRO when coming into RGB space. Some are better at staying "generational"... where the chroma is much more steppy and designed to survive re-encoding, some are "presentational"... with a pleasant blur to the chroma that won't duplicate as well, but looks better and keys better... in this way, it's exactly the same as DV 25 codecs.

In this case, I captured via HDRack and used its codec for loading the files into AE. This codec is based on the P2 Viewer source with has some issues, one of which is a rather steppy representation of the chroma.

ulisses said:
Your key is good, but i can see some DV compression artifacts (blocky) that should be avoided with 4:2:2.
Click to expand...
DVCPRO 100 and DVCPRO 50 both have compression artifacts, the same as miniDV or DVCPRO 25. DVCPRO 50 has less compression than DVCRPO 100, but both will show compression artifacts during the matting process, or heavy levels/color correction. Compression can be independent of color space. You can have a compressed 4:2:2 image, or an uncompressed one.

ulisses said:
The blue screen article you posted was using 1080 uncompressed, it was recorded direct in Velocity system without the DV compression, which should be better of course.
Click to expand...
Important to note... the key example movies and stills on my site are NOT from the uncompressed footage I recorded... they are all from DVCPRO 100 1080 source comped at 720p, converted to RGB by Raylight.

Regards,
 
Jim Arthurs said:
DVCPRO 100 and DVCPRO 50 both have compression artifacts, the same as miniDV or DVCPRO 25. DVCPRO 50 has leImportant to note... the key example movies and stills on my site are NOT from the uncompressed footage I recorded... they are all from DVCPRO 100 1080 source comped at 720p, converted to RGB by Raylight.

Regards,
Click to expand...
Hey Jim,So do you think the footage recorded to the P2 cars is just as acceptable for great reults?Also, when you say that ylou blur the red and blue channels, how much do you blur them?
 
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