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C300 Green Screen Shoot

 

I have an upcoming Green Screen Shoot. Mid shot on the Canon C300. I tend to always use the C300 in its Cine Log LUT. Most places that handle post seem to have no problems with this method and like the color space. But one facility said the last time I shot the Log LUT / Green Screen they had a very hard time getting color back into the image. I think they are a little "green" in the grading department, but none the less, I have to work to their level of experience...

A few Questions for the post folk out there:

A) Is it best for us to shoot LOG LUT then key from the raw ungraded image, without applying a Log LUT - Rec 709/Video curve? Then apply grade at the very end.

B) Is it best to shoot REC 709, then key directly off of this?

C) Is it best for us to shoot LOG LUT then have post color correct the image to a good colorful video space, then key the image?

D) What camera settings are people finding work the best with the C300 on Green Screen..?

My client is 'time poor' and wants the fastest workflow. I just want to make it look good and work well for their post route.

Thanks in Advance folks. Dan Freene ACS Sydney, Australia.


 

> A) Is it best for us to shoot LOG LUT then key from the raw ungraded image, without applying a Log LUT - Rec 709/Video curve? Then apply grade at the very end.

I can't say for sure, but I do know that they'll be working with a very desaturated image if you give them ungraded log and they don't do anything to it themselves. I'd think they would do some sort of rough grade just to get something green enough to use.

> C) Is it best for us to shoot LOG LUT then have post color correct the image to a good colorful video space, then key the image?

If the VFX house can't do this then this seems like a good idea. At least give them a rough grade good enough for them to key on, and then polish it later. It's not unusual to do two passes, one optimized for green and the other the final grade.

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Art Adams | DP San Francisco Bay Area


 

I have used the C300 for post-production and I have some recommendations you may want to consider..

It is an 8bit machine and this means a very limited latitude in my opinion, a great camera but I limited so stick to Log to maximise your dynamic range and if possible use a linear approach. This means;

- Capture in Log

- Do not apply any grade

- Using DaVinci resolve or Nuke or any other true 32bit floating point tool linearise the image and apply your technical grade here

- Export the images as EXR 16bit half float

- Do all your effects and comp in linear in Nuke for example using a LUT to remove the monitor gamma

Keying this way will be much easier and predictable and NEVER grade a plate for keying, that defeats the purpose unless it has been badly exposed in the first place and you are just trying to correct for it. The comp artist keying will also use tons of tricks to make sure you give them the material in its purest form (think of it as a NEG you don't want to mess around)

- Finally deliver in the format of choice for your final grade, DPX 10bit log for example if you are using Resolve, I found that the linear pipeline in resolve is not as good as Baselight.

BUT

Unless you are really against the wall for time I would suggest to avoid green screens, the spill is something that even with the most modern tool still looks awful and is simply something we can't do.

At Realise we do not do green screens, we roto everything by hand against a grey or sympatethic background. Painful but looks awesome and your DoP will be happy he only needs to light the scene, not the green screen.

Hope that helps

Jordi Bares Deputy Creative Director

Realise Studio www.realisestudio.com


 

My thoughts as a post guy (and author of a couple of color correction books) is that if the facility that is using the stuff may be "as green as your screen" then my suggestion would be to simply shoot REC709.

Green screen is going to TEND to be shot without some of the extremes in exposure that you would likely have shooting a non-studio/greenscreen image, so the need for LOG is not QUITE as important.

And if speed and ease of post - not to mention the fact that you'll have more control of the way you image looks - I'd go REC709/Video curve. Obviously if you were dealing with a very qualified colorist and you were going to be AT the grading session, LOG would give you more control/possibilities to get the image where you want it, but this seems to be a case where delivering a controlled image in a color space that is comfortable for the post house is the way to go.

The other alternative would be to shoot LOG and then do all of the conversions to REC709 yourself, but that just means a LOT of extra work and expense for YOU without much benefit or payback.

It's a warning sign for any facility to say that they had a hard time getting color back in the image from a LOG image, unless you REALLY screwed up the exposure/balance.

Steve Hullfish contributor: www.provideocoalition.com author: "The Art and Technique of Digital Color Correction"


 

> My thoughts as a post guy (and author of a couple of color correction books) is that if the facility that is using the stuff may be "as green as your screen" then my suggestion would be to simply shoot REC709.

I would concur. Something that has popped into my head that hasn't been mentioned is that if you have to apply a LUT before you perform a key you then end up taking a REC709 image into the grade anyway, do you might have well just shot REC709 in the first place?

Andrew McKee Film Editor


 

By the way, when looking at a Chroma Du Monde chart I've discovered that the color matrix that comes closest to Rec 709 is the EOS Standard matrix. Red pops a bit but the other colors generally hit the other targets, in particular green.

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Art Adams | DP San Francisco Bay Area


 

I did a bunch of Cromakey Ivs for a broadcast doc recently on a c300

Shot rec 709 and normal2 colour curve, the edit was done in FCPX and the key is so clean its scary!

Ill try and get some frames to post.

Michael Sanders

London based DP Editor.


 

> > The other alternative would be to shoot LOG and then do all of the > conversions to REC709 yourself, but that just means a LOT of extra work > and expense for YOU without much benefit or payback.

Shooting log and doing the conversion yourself changes the quality of your final image. Of course, principally a log curve gives you more latitude and more grading / post flexibility.

But a log signal can be a tricky thing when used in combination with strong compression and low bit depth. And that is obviously the case of the C300.

Also, it is important to consider the order of the signal treatment in a specific camera, from the moment where light is hitting the sensor (a photo-linear signal in the first place), a/d conversion, debayering, divers amplifications & matrixes, conversion to a logarithmic or video linear signal. Those things most of the time happen in higher bitrates than the recording. AFTER all this, the final recording / output / conversion to the actually recorded (low) bit depth / (strong) compression) etc. is happening.

That means

1) Doing Rec 709 InCam: Green is graded to comfortable posthouse level BEFORE compression, BEFORE 8bit color depth conversion etc Š

2) Doing Rec 709 in Post: the "log" Green is graded AFTER the log signal suffered from compression, 8bit conversion during etc Š

Which means that the decision of doing REC 709 or Canon LOG is affecting the final green screen quality. I'm not saying that is is necessarily less good, because, even if one has to cope with a compressed and low bit depth signal when LUTting from log to videolin in post, post production products may still cope in a better way with this formerly compressed signal than the camera the non compressed signal, since they do not have the same constraints as a camera manufacturer, such as realtime processing obligation, little camera body which needs to be lightweight and work under tough climate conditions etc ...

But I still could imagine that the meanwhile known green screen problems of the C300 maybe partially du to the combination of log and strong compression. I therefor shoot my C300 Green Screen stuff on REC709, which I do not with the ALEXA on ProRes or DNXHD.

In the old times of the D-21, for instance, ARRI strongly advised not to shoot in logC and to record only on Nanoflash or P2 recorders exactly because oh this problem.

Frank van Vught (Paris & Munich based DP, sometimes working as a consultant of ARRI)