Welcome to our community

Be a part of something great, join today!

Log in
  • 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 :)

Gunleik / or anyone with green screen knowledge!

Jon Schellenger

Jon Schellenger

REDuser Sponsor
Joined
Feb 14, 2007
Messages
194
Reaction score
0
Points
0
Hi Gunleik,

I have been reading your posts for a while now, and I really need your help with something. I have been doing a bit of green screen work with my red camera and I am not sure what to make out of the results. We have been using a studio here in Port Saint Lucie.

The studio is designed mostly for a TV set, and we are able to use the RED on weekends when we can create some really advanced television work. IE: commercials and infomercials.

We have a cyc wall in place and for the most part it is evenly lit.

I have been researching the RED and doing a bunch of shooting with it since it was shipped to me last April. I am familiar with most of the issues that the camera has- one being the IR issue.

I am using the newest version of build 16. I have Pancro ND/IR filters for outdoors, but nothing for indoors.

Our lighting for the green cyc is a kino flo package balanced to 3200K. When we have the talent on the green screen, they are usually lit with the 3200K kinos along with a couple of arri 650s. All our other camera (not red cameras) can do a fair job keying the talent out with this lighting package and setup.

We sometimes gel our lights with straw filters, or blues just to give a nice effect and highlights.

We usually light everything evenly, and it is at the correct exposure.

On some of the shots when the talent is furthest away from the screen, those key out fairly easy. On the ones where they are standing on the cyc (full body/wide shot) it seems I am getting a thin line around the talent. When using keylight and shake it seems to be a real pain to remove this small edge line around the talent. When zooming in real close to inspect it, it seems I am getting a thin line of noise around the subject. I know this line could be spill, but it is behaving very strange. Why the noise?

Can you help me determine what this is?

I have heard from others that we should gel everything CTB? Why? Is this for the IR from tungsten? What is the tungsten lighting really doing to the red? Should I never use tungsten again? Even on location? It does not make sense to me.

Should I get a hot mirror for indoors? Will this help?
How will I even know when I am having poor results with tungsten? It is hard to know what to look for.

Can I send you a link to a still tiff image of the talent and see if you agree that we have some kind of a noise issue?

We have no HMIs in our studio- everything is tungsten. We also do a bunch of slow motion stuff, so I really don't want to lose any stops, but if I have to to get a better result, I will?

Any special ingredient settings on the camera I should be using?

I come to you because I thought you would have the most knowledge on this.

I had Damian Allen come to see us in Florida- (he is a keying specialist with keylight). Even he was stumped on this issue.

My settings were- 4k and a few 2K shots. Mostly 4K though- 320 ISO. and balanced to 3250 or around that area after white balancing.

We were using the red 18-50 and on some shots using an arri ultra prime 85mm. Shutter was around 48th of a second unless doing slow motion effects.

Help!!!
 
Sounds like you are underexposing the blue channel with the tungsten lights, thus getting noise in the blue channel. My guess.
 
I will see if I can upload a still frame so you guys can see
 
I can't help with identifying the cause of the green spill noise, but I can help clear up the light issue.

The blue channel on RED gets noisier under tungsten lighting as the sensor is 'balanced' for daylight (5600K).

Under builds prior to 16 it was a noticeable issue when shooting Tungsten (3200K), the blue channel was starved of blue light and hence the noise to signal ratio was higher than the other two channels. This added a 'grain' to the image.

Build 16 reduced the blue channel noise considerably due to the way the noise pattern was handled in camera. I have shot a lot under tungsten on build 16 and the noise isn't really an issue any more (unless its low light).

To get the best (least noisy) image from a RED however it is best to use daylight balanced lights (such as CTB'ing tungsten or using HMI's).
 
Well that certainly explains a lot Ed!

I have seen the noise you are talking about for sure in the blue channel. Even on build 16. This helps me a ton because I do want the cleanest image possible. So you are basically saying that I should keep the camera at 5600K and just throw ctb to balance it out and shoot with that setup. With that done, how much lower will the noise be in the blue channel?
 
yes, I have some, but I want to get you guys the best - I have a 4k tiff ready to go- but how can I upload it here. I really don't want to compress it. It is right off the press of redalert and she is running at 48 megs
 
Status

While it's true that you will have an "easier" time with daylight balanced lights, you can do a fine job with Tungstun provided things are exposed well. From what I can read, it would seem like you have some dark shadow and spill issues. I highly recommend looking into Keylight.. It's wonderful for such things. Otherwise the art of the rim light is your savior here, it will allow for a strong signal line which should separate your talent from the screen. As for their feet on the floor, not much you can do about that.
 
Jay,

Can you take a look at a still- and is there anyway you can post it for me?

I really want to get this up so everyone can look at it, but I don't know how. It is 48 megs.
 
yes,

I even had Damian Allen take a look at this- he wrote books on using keylight. The guy is amazing, but even Damian was stumped over this. I think you guys are on to something with this noise in the blue channel. I am really considering backing off and going up to the 5000k for the sensor and ctb. If it really make my job easier, then I want to do that. I am shooting on Sunday in the studio. I really want you guys to take a look at this tiff and see what you think- can I email it to someone who can post it here?
 
The image looks solid. My only suggestion might be to review this tutorial on Keylight from Andrew Kramer. This simple video helped me improve my keying a great deal. Damian Allen may have been aware of all these adjustments, but it might help. Good luck.



http://www.videocopilot.net/tutorials/basic_color_keying/
 
I had a look at the TIFF you provided. By chance, did you use some sharpening filter on the image? During the export from RAW to TIFF?
Turn it off and that should solve your problem.
The thin line around the talent looks definateliy like sharpening artifacts.
 
Status, I took the image and separated the RGB channels. As suspected, the Blue channel is seriously underexposed, and has the largest artifacting around the talent, as well as noise on the screen and Shirley. The red channel also has some problematic artifacting, and the green channel has the least.

Daylight balanced lights for the screen should help, but this really looks like a compression problem with the build IMO.

Also if you can, backlight the talent to help separate her from the background. This may help. Good luck and please post again if any of this works, I am planning on doing many Greenscreen shots when Scarlet ships. I would be interested in hearing from the RED Team on this one too...
 
First of all- THANK YOU GUYS!!!! As usual, you guys have really helped me out.

Freezer- Damian and I went back to investigate the sharpening issue. We exported another series of clips with the sharpening turned off in RedAlert. I did learn about watching out for any type of sharpening while I was with him. He told me exactly what you are saying and that it will screw up keying in some situations. Even with sharpening off, we still ran into the issue, however, it was not as bad.

DudeKill- I appreciate you breaking those channels down. Damian and I were doing the same thing in shake and we were very surprised to see that there was that much noise in the blue channel. Very scary to say the least. I now understand that with a white balance of 3200 or lower, it starves the blue channel of so much light that it almost acts as if the gain has been turned up to 18db or more.

Do you have any clue as to why I would have any artifacts in the Red Channel? That one has me a tad bit concerned. The Tiff I posted was exported directly out of RedAlert. To be honest, I can't remember if that was the one that might have had the sharpening on it. Sorry about that. I do know that Damian and I re-exported some with the sharpening turned off. That may be why you are seeing some of the artifacts. I am just not sure. One quick point- this shot was done with the RED 18-50 lens.

For the most part on all of our shoots we have been using an 85mm arri ultra prime. I have also rented an 18mm arri ultra as well, but for the most part, anything wide was usually done with the red 18-50.

So guys- here is what I have done and what I am planning on doing this weekend in the studio. Double check me....

I decided to rent some Cooke S4 Primes. One is a 16mm and the other is a 75mm. I thought I would try out those lenses for green screen.

I ordered some CTB - taking our tungsten lights from 3200 to 5600K and I will stay at the factory setting of 5000K for the RED. I will also do what you mentioned dudekill- I will crank up a backlight a tad to help break her away from the background.

My ISO will stay at 320 as always. Anything else guys?
 
Dudekill and everyone....

Let me ask you this- am I correct to understand that if I leave the camera at 5000K, CTB my tungsten lights, and make sure that the picture is correctly exposed- will my blue channel look almost as clean as the red and green????

If so, you made a very happy film-maker here! If that really is the case, then I can see why this camera would be absolutely amazing to key with.
 
You must log in or register to reply here.
Back
Top