night green screen questions

[Tom Lowe]

I am very curious to learn how I might be able to shoot my actors in front of a greenscreen, and then insert them into a night timelapse shot.

To give an example, how can I take one or two actors, maybe just standing there, or perhaps a couple kissing or something, and comp them onto a moving 24p timelapse of stars moving across a night sky like this plate below (minus the sunrise on the mountain peak) which I would shoot on my DLSR or RED at 4K...



What would be ideal for me is if I could bring along, say, a 12x12 greenscreen and shoot my actors on location, in the very places where these timelapse plates would have been shot, and somehow correctly light and expose them to fit perfectly onto a composite with the timelapse plate. This, rather than trying to match wardrobe, hair, etc, a month later in a greenscreen studio in LA.

It is more or less difficult to composite against a dark or even black night vs against a glowing sunset or regular blue sky?

Even with all the technology George Lucas has at ILM, I have to say that the final sunset shot on Tatooine in Sith did not look convincing at all to me.

It seems like this type of greenscreen shooting might be tough, because if you are outside on location and it's dark, and you are lighting a green screen behind your actors, wouldn't you be getting some "backlighting" around their edges and hair that would seem unnatural for a shot supposedly taken against a night sky?

thanks!

[Steven Parker]

Sounds like a sweet shot!

Don't know if this works with your visual style for these night exteriors, but I would go with a soft toplight (at key or just a bit under) on your talent with minimal fill light, almost like creating silhouettes of your couple. Motivated by the stars themselves. That way they merge with the very dark foresty feeling in your example.

As far as halos, I think I would pull them as far away from the greenscreen as possible and use as long a lens as possible to minimize the risk of spill. Soft light on the greenscreen to minimize bounce. Depending on the shot size you need of your couple, hopefully you can get just enough green around them to pull a garbage matte.

It could be weird to have a wide< plate and compressed foreground element, but if you're close to your talent on a wider lens you'll need more than a 12x or you're going to have spill/reflectance issues.

Wow, the night exterior aspect does make it more difficult! ;)

My greenscreen work has always been day oriented, so hopefully others will chime in...

[Jim Arthurs]

Tom, I personally think that trying to work with the actors on location AND deal with the time-lapse aspects of your shots is more trouble than it's worth... besides, if you bring out a green screen, then you have to light it on location, as well as light the talent. No aspect of the "natural" environment (sky light, etc.) will impact or improve the photography of the people, as it's two completely different ranges of exposure. I guess what I'm saying, is that your people lighting setup will be "artificial", no matter if on location or in studio.

One tip for this sort of subject... string up a large black in front of your greenscreen and light your subjects to suit in front of that. Then remove the black and illuminate the screen to the proper level. Trying to judge the lighting with all the green spill is difficult, so make it easier on yourself by using the black. Remember, the green spill, from the software's point of view, is actually negative illumination, and needs a certain amount of white light fill added to simply read as black and not an area of the image with the green stripped from it crawling with noise.

As Fovean mentioned, back away and keep the size of the screen as small as possible to cover the action and no more...

Regards,

[Steven Parker]

Well said, Jim, and the 12x solid is an excellent, excellent idea.

I think the whole nature of the shot is artificial, but meant to give an emotional impact. In that case I think I would still want to do it on location, provided schedule and support and so forth allows for it, because actors and crew respond to that emotion as well.

It is quite an endeavor for what - 6 or 8 seconds of screentime? But what seconds!

[Tom Lowe]

thank you so much for these suggestions, guys!

keep the knowledge coming please.

Yeah, for me, knowing actors, it will be better, if there is any way to do it, to get it done on location, rather than trying to get actors who are working for SAG ultra-low scale to show up in LA for greenscreen a month later in the same wardrobe, and hoping their mood, facial hair, etc, is all the same.

[Evin Grant]

I would shoot in the same location but durring the day, probably afternoon. Shoot with a good 50 IRE greenscreen and just hard sunlight on your actors.
When you get into post do your key and then CC the actors blueish and bring down thier gamma to match the scene. This will give the impression of moonlight and you can then have control over the exact matching too. It will be very hard to get a good key if your greenscreen is significanly brighter than your subject, then again with RAW 4:4:4 Redcode maybe not.

[Jeff Kilgroe]

A lot of good suggestions here.... If the picture you posted is truly representative of what you intent to comp the actors onto, perhaps greenscreen isn't the best choice? I would consider a blue screen in this situation - it may hold some unseen benefits.

Keep the actors as far forward from the blue/green screen as possible to minimize any light reflection or spill from the screen. Afternoon lighting as Evin suggested would probably be best and should give you a lot of color latitude to work with in post. You can always darken it up and adjust color to fit the night setting.

[Steven Parker]

Hey AppliedVisual--

Can you elaborate why you think a bluescreen could work better than green?

So funny; when I started shooting greenscreen, it was "Expose greenscreen at Key Light Exposure!" Then it was a stop over key, now I hear a stop under... who knows? I do what the VFX guys ask of me. I suspect it's because post software for a shot like this has developed much more in the past few years than the on-set tools for a shot like this.... lately for me it's been Greenscreen or DigiGreen, no one ever mentions blue anymore....

Wonder how long it'll be before we're talking redscreen comps? No pun intended, it's just another color channel...

[Robert Niessner]

You can't use redscreen with humans, it would interfere to much with the skin color.

Another idea worth considering would be to shot on a blackscreen and use a blend mode to composite. As you have a very dark backplate this might be a much easier solution - but it depends on how you want to have your couple look like in terms of lighting. Ask your vfx supervisor what he thinks. You even could try this one easily out - just take a photo somewhere with a black background and try to composite it on your background footage.

[Jim Arthurs]

So funny; when I started shooting greenscreen, it was "Expose greenscreen at Key Light Exposure!" Then it was a stop over key, now I hear a stop under... who knows? I do what the VFX guys ask of me. I suspect it's because post software for a shot like this has developed much more in the past few years than the on-set tools for a shot like this.... lately for me it's been Greenscreen or DigiGreen, no one ever mentions blue anymore....

The stop is dependent on the chroma quality and the luma level of the screen. GOOD paint (like Composite Components line of paint) is designed to be the right luma when illuminated to the key light level of your setup, and is of sufficient chroma at that light level. Everything else I've found (other paint, fabric, paper) needs to be evaluated by waveform/vector if possible to hit the sweet spot. Some cheap stuff just doesn't work... pump up the luma enough to get proper chroma and you find the blue/green difference is too small and the screen is almost lemon-white with a spill that hues to the cyan when corrected.

One other factor is the paticular characteristics of your sensor/stock. I've found most of the CineAlta/700 series footage to react better at a half to full stop over for green and exhibit less noise...

Blue is better than green in many cases, with blonde hair, yellows in general, etc. You also need to light it to generally lower levels to get the proper saturation, which has the side effect of reducing the spill. Of course, when a video camera exhibits a crappy blue channel you shouldn't use it, but I've had terrific results with the HVX and blue. And of course film... I still own a little transmission Stewart bluescreen back when I did blue screen the old fashion way... with an optical printer. Which is another story for another day.

I love blue and predict blue will make a big comeback due to, ironically, the color RED.