Green Screen Advice

[Matt Siegel]

Hi All,

I’m shooting an underwear commercial next week and it’s the first time I’ll be shooting green screen. It’s a series of five short spots and the reason I’m shooting green screen is so that I can change the background in each to a different pastel colour, so it’s not at all complex VFX, I just don’t want to have issues with keying in post.
 

I’m shooting it at an SAE-owned green screen studio here in Byron Bay, Australia. The green screen is about five meters wide by three tall. I’m shooting 4K DCI C-LOG 2 on a C300 MKII at 10-bit 422.  It’s all on sticks and lighting is the main thing I’m worried about. I’m planning on lighting the background with two Aputure 300d Mkii’s with Light Domes, an Aputure Nova P300c through a 4x4 of full I grid for the key and a Godox VL 150 for hair/rim. I’ve got a Mole 2K fresnel in my back pocket if I need it, plus a couple of Phottix 1x1’s as needed.

None of the videos has more than one actor on screen at a time and the shots are mostly medium closeups, closeups, medium wides, etc, of actors modelling the underwear, so nothing too wide. They’ll be doing a fair bit of moving about, dancing in place to some upbeat music.

I guess I’ve got a couple of questions off the bat:

1. Is that lighting going to be enough to cover the background?

2. What’s the best way to insure I have the green screen evenly lit?
3. Any recommendations or suggestions based on your first time shooting green screen?

Thanks for taking the time to respond to my questions. It’s my first time working with a new client and  I really want it to go smoothly.

Best,

Matt

[Tomasz Brodecki]

Sure, with careful placement and/or a bit of diffusion, the two 300s can be enough.
I'm mostly going to advise lighting the background criss-crossed (right light shines on the left part of the background and vice versa), so that you avoid hot spots and provide a more even illumination.

[Satsuki Murashige]

I’m not familiar with those lights, but I’ve lit plenty of medium-wide shot green screens with just two 4x4 Kino Flos (just the green, not the subject). So I think if you back the hard lights off for more spread and use heavy diffusion frames in front, then you should be fine.

Once you need to see the floor too or multiple people/two camera angles, you will need to light wider and start thinking about rigging overhead lights. Also, the wider you can light the green screen the further you can pull the subject away from the screen, which will help with green spill and also throw any smudges or dimples on the cyc wall out of focus. 

As Tomasz says, place the lights on the left and right side of the background just out of frame. If you need more light in the middle, you can place a large soft light on the ground under the screen. If you don’t have something like 4x4 Kino for this, then you can bounce a harder light into a large white card on the floor. Often this can be done from the floor, so no need to rig an overhead.

I would also black out/flag off as much of the off-camera lit green cyc/floor as possible to kill spill. If the stage has a few folded 4x8 showcards (v-flats) that stand up on their own, those are great and can double as negative fill or a large bounce source for a book light key. Otherwise, you’ll need a few floppies.

[Satsuki Murashige]

I would also consider not shooting Log (especially the super flat C-Log2) in a 422 10-bit codec for studio green screen. Unless you have some bright specular highlights, deep shadows, or super saturated colors that you need to hold, a super flat Log image won’t be of much benefit and you’ll have to stretch the codec quite a bit in post. I’d suggest something with more moderate contrast and saturation like Rec.2020, or at least C-Log3. I wouldn’t necessarily go all the way to Rec.709 since it’s helpful to keep a little bit of flexibility in post to fix skin tones or product hue shifts that may occur with some LED lighting. 

[Matt Siegel]

Thanks to you both, that’s very helpful.

2 hours ago, Satsuki Murashige said:

I would also black out/flag off as much of the off-camera lit green cyc/floor as possible to kill spill. If the stage has a few folded 4x8 showcards (v-flats) that stand up on their own, those are great and can double as negative fill or a large bounce source for a book light key. Otherwise, you’ll need a few floppies

In this context, is green screen spill essentially the same as  any other light spill that we want to try and control? Conceptually it’s just reflected green light, right?

[Matt Siegel]

Oh, and regarding bit rate and LOG flavours, I have three options, I suppose:

1. 4K 10bit 422

2. 1080 12bit 444

3. 4K 16bit PRORES RAW

Does anyone have thoughts about the pluses and minuses? I was thinking 4K RAW to start but given I’ll be delivering at 1080, maybe it’s better to just get the extra info from 12-bit and save some file size? 

Regarding LOG and gamma, that does make sense. Anyone with experience of C300 mkii on green screen had more success with one of Canon’s non-LOG profiles? 
 

[Satsuki Murashige]

16 minutes ago, Matt Siegel said:

Thanks to you both, that’s very helpful.

In this context, is green screen spill essentially the same as  any other light spill that we want to try and control? Conceptually it’s just reflected green light, right?

Yes, although I think it’s more critical with chroma key work for obvious reasons. 

[Matt Siegel]

1 minute ago, Satsuki Murashige said:

Yes, although I think it’s more critical with chroma key work for obvious reasons

That makes perfect sense. Thanks so much.

[Satsuki Murashige]

6 minutes ago, Matt Siegel said:

Oh, and regarding bit rate and LOG flavours, I have three options, I suppose:

1. 4K 10bit 422

2. 1080 12bit 444

3. 4K 16bit PRORES RAW

Does anyone have thoughts about the pluses and minuses? I was thinking 4K RAW to start but given I’ll be delivering at 1080, maybe it’s better to just get the extra info from 12-bit and save some file size? 

 

1. All things being equal, 4:4:4 or raw would be preferable for chroma key work. 

2. 4K vs 1080 for 1080 finish. Generally, I would always want 4K since it should key better as the pixels are smaller and also the noise will be smaller. Plus editors always seem to want to punch-in in post these days, especially with chroma key or flat backgrounds.

You’ll have to decide if those advantages  outweigh the downsides of chroma sub-sampling. But in my experience, they do unless you are shooting very saturated blues and reds  where the sub-sampled edges would be very obvious.

3. I haven’t used the C300Mk2 in awhile, so I wasn’t aware it could output 4K 16-bit raw. That would be ideal, however those files sizes are going to be massive. Last time I had to get raw out of that camera, I think it was only 10-bit Canon RAW to an Odessey. Big mistake, never doing that again. Luckily the internal recording was fine. 

[Robin R Probyn]

Yeah re spill , I would light the screen 1 stop lower or at least make it lower than your subjects ..  false color if you have it is  handy for checking your GS..  but these days its all a lot easier than it used to be ..   they will junk matt around the subject too , so you don't have to worry about  a corner  of the scree being dark / wrinkled .. the whole screen doesn't have to be evenly lit.. just the area behind your subject ..   green spill is a pain with blond hair ,and seeing your in Byron Bay Im sure you will have some blonde models .. ?  .. keep the action a decent way in front of the screen and don't over light it ,   I wouldn't stress too much though , these days you can key off an unlit green bin liner ..  make sure the underwear isn't green , or have a blue screen too just in case .. !

[Matt Siegel]

Thanks Robin! That's all very helpful. Funnily enough, only one of my three actors is blonde, but still, it was a safe bet :)