I'm all about saving myself as much grief as possible when shooting green screen. I'd get a REAL desk. I wouldn't have the talent interact with anything green.
You could really shoot yourself in the foot with a green desk. I bet you want quick turnaround on these shots. The prospect of using Rotobrush looms large in your green desk scenario..... which will slow you WAY down.
I intend to do an hour show on a weekly basis - so definitely want my workflow to be as trouble-free as possible.
I will be using a real desk.
What i'm deciding at this point is
a) Do I leave its wooden top as is (or maybe drape some black fabric over it)
b) or do I paint it with the same Chromakey green paint I've got on the back wall
I'll be doing my work with Adobe CC and have access to some virtual sets as well - and my camera will be in a single fixed position throughout the show - so would be easy enough to mask out the front of the desk.
So my main question had to do with getting spill from a green desktop onto the talent, because there are constant warnings about keeping talent far enough from back wall to avoid spill (but oddly no mention about problem with green desk - but I imagine that would be an issue, wouldn't it?)
Aside from that spill problem, am I missing something else in terms of roto-scoping? Because I certain don't want to introduce significant amount of post-work into my workflow if I can avoid it. That said, would open up some creative possibilities if I could easily work with a virtual set - which is why i posted the question.
Thanks for your help and any further comments.
If you want to replace the desk then you are almost certainly faced with some roto of the hands and arms. This can still be a major problem. Whenever I do this kind of stuff, and I have done hundreds over the last several decades, I put a sample of the real replacement desktop down for the talent to use when they are going to have any part of their body interacting with the desktop, and most important of all - I shoot some tests. You must make sure that you kill all reflections because desktops tend to be very shiny. You do this by the positioning of the lights that are lighting the green screen. If the lights on you talent fall on the background then you need to be extra careful that the angles don't contribute to the reflections. For my big productions if you turned off the lights on the background it dropped about 4 or 5 stops (hope you know what a stop is). If you have a scope or waveform on your camera (an app called Cinemeter II will do it for your smart phone) you should have the background at about 50 to 60 IRE max if your talent's face is at 70 or 80. Keylight and most other keyers can easily pull a good key with the background as low as 50 IRE. The closer the background luminance level is to the tones in the face the harder it is to pull a good key. If you have a background that is equal to or greater than the highlights on the face you are in trouble unless you are shooting 4:4:4 uncompressed with a professional camera. Take it from someone that has made about 1/4 of their income in the last 15 years fixing poorly shot process shots for others because they couldn't pull it off and could not reshoot.
If the actor is picking up objects from the desktop the piece needs to be big enough to allow those objects to rest on it also. I've done this with really complicated virtual sets where the actor moves all over and interacts with several pieces of virtual furniture. Sometimes it's easier to just hide the hands behind something that you can key out so you don't see the desktop. You do this in the design of your virtual office. I have use something as simple as a C-stand and a piece of foam core. Remember, if you talent is walking in front of a virtual desk you don't have to worry at all about keing what is behind the desk.
The other important part of the equation is to make sure that you know how far your virtual camera is from your talent and how that works out for your virtual set so you can match the camera position of your virtual set. This is pretty easy to do by putting something in the shot that you can measure and then measuring the distance from the camera to the known object. I often use a full flag or a couple of apple boxes set on the edges of the set that I can easily remove with a garbage matte.
Just throwing a black cloth over a desktop isn't going to save you any roto time. The only other possible way to make this work without roto is to put a blue top on the desktop and a green screen behind then use two keyers, one for the blue, one for the green. I've successfully done that more than once, you just have to make sure you don't have reflections and you don't have color problems with the things the actor is going to handle on set. I even used a red matte show card.
I hope this helps. Planning and testing is critical.
Thank you for the detailed answer.
I'm going to be using a Panasonic GH4 which allows you to capture 4:2:2 colorspace when exporting via the HDMI port (I'll have an external recorder (Atomos Shogun).
I don't have any background in photography or videography (and haven't done much of this for the past year, because I've been focusing on other things) - so any tips are appreciated (and feel free to link to basic articles i should read or videos to watch to get up to speed).
In terms of "just throwing a black cloth over a desktop isn't going to save you any roto time" - if I use the black cloth, that would be instead of using a virtual set; I would simply film the host(s) at the table and have greenscreen in the background. And that would be okay for the type of informational show I intend to have.
But if painting the desktop green (or blue - or using greenscreen or bluescreen fabric on the desktop) would allo wme to have hosts interact with real objects (like laptop computer, papers etc) while setting them against a virtual desktop, that's something I might consider.
I suspect i'm misunderstanding something, because aside from light spill, i'm not sure where the rest of the problems come in in terms of needing roto.
I'll' do some simple tests by laying a greenscreen painted board on top of the desk - maybe it will be clearer what I'm in for at that point.
Also welcome concrete suggestions about how much lighting, light meters etc . . .
Right now I have 4 lightboxes on stands, and 4 lights which I got earlier with white shoot thru umbrellas. I think all of these at 5600K but will need to double check. Is there something I can put outside of the box for the pair illuminating the screen to get that luminance value down?
Light follows the inverse square rule. Double the distance 4 times less light. If your space is small, say 15 feet from the camera to the back wall you have to use angles or cut down the light with scrims or flags or bounce it or angle it. There are lots of resources on lighting. Just using light boxes (light boxes don't use umbrellas so you need to learn the terms) or diffuse through umbrellas may not be the best solution for your project, but with some fairly inexpensive light modifiers like foam core and black show cards or poster board or even better matte board, or some thin plywood or particle board and a little spray paint and some way to hold up or anchor your light modifiers you will be all right. Light modifiers are more important than the lighting instruments.
Let me tell you a short story. In the early 70's I had the chance to take an extensive lighting workshop at UCLA with one of the greatest directors of photography there ever was James Wong Howe. I was so excited to see all of the great lighting instruments that I had read about and seen hanging in the racks of the grip trucks. On the first day of the workshop class he showed up carrying 4 Mickey Moles, a very simple open faced focusing flood light. In the studio there were a few light stands, a bunch of C-stands, and a couple boxes of light modifiers (most people think soft boxes, umbrellas, grids and other things you attach to a light are modifiers but there are so many more) and other things to control the light like flags, scrims, dots, fingers. some black wrap (black aluminum foil) and a little bit of furniture. OK, I thought, start with the basics. Then he said "For the next six weeks this is our kit." That's exactly what we did. Almost every possible scene that you could imagine was setup and lit with four 1000 watt open faced instruments and some light modifiers. it blew my mind and made me a much better cinematographer. Even today I own many more light modifiers than I do lights and I never show up on a shoot without some way to control the light - even outside. Here I am on the set of a western I'm a part of talking to the director and holding a folding shiny board, silver on the front for more light, black on the back for less.. a light modifier.
Here we are getting ready for a shot outside, nice diffused light and just to the left of the scene a 10 by 1/4 scrim.
If I can find some shots of one of my green screen setups I'll post a few. If you put up a photo or a drawing of your set I'll try and help out.
Just for fun take a look at this site. While he uses a bunch of different lighting instruments, notice how many of the setups use light modifiers of some kind. Lighting - Matthew Scott Cinematography Blog
Thanks - will try to take some pics and post images of my setup over the next few days.