It’s been an intense month of filming out in the Middle East. I have done more shoots with Camels and out in the desert than I care mention, been back and fourth to Abu Dhabi several times and had some very cool studio shoots.
One of which was a good old Chroma Green Screen shoot. Now Green Screen is two words that can often bring about a bit of confusion. How to set up it up and most importantly how to light it to get the best cleanest KEY possible.
Production always look to the DOP as an expert. The reality is most DOP’s have never attempted a Key themselves (as they are not working in post) so they generally only know how they have lit it before and the feedback after the project has been completed. The Editor is really the technical genius when it comes to actual compositing and keying! I always find it a little weird how DOP’s and Editors rarely speak, considering one is ‘gathering the food’ the other ‘cooking it’ you would think they would talk a lot more… as no matter how good the chef is, the better quality the produce the better the meal!
Many big feature films especially Sci-Fi ones like Avatar have green screen elements that you wouldn’t have ever noticed or knew were shot green screen. When you see behind the scenes of these shoots in mags like American Cinematographer (which I think is the Bible for any DOP or aspiring ones) always looks so effortless – is it because they have stronger post production keying tools..? What’s the deal..?
I have just googled Green Screen and a whole load of videos came up about ‘how to do it’… Many were a little basic and the Keys on the ‘how to’ demo videos looked pretty crap anyway… With fringing around the arm when the person moved… Definitely, what you want to avoid!
As Green Screen is one thing that has always perplexed me a little and not being able to find relevant info on ‘how to do it’ to a professional standard I have put together a few tips from my past experiences – which there has been many… All of these tips are after trial and error of shooting both Green and in the old days Blue screen – I don’t mind admitting in the past of I have done both a good and bad job of lighting these… And it is pretty much all about lighting!
After just finishing a recent green screen shoot and having extremely positive feedback from the Director and Post House ‘Green screen edit is going really well. Thank you for an evenly lit green screen (you made the editors really happy), and thank you for generally outstanding lighting. You’re an artist sir and would enjoy working with you again’ – yer always good to blow a bit of smoke up your own bottom… (not literally! don’t try it at home without a someone sensible present).
Anyway, I thought it was about time to share my TOP TIPS with DOP Blog and spread some ‘light’ on the subject (awful pun I know)…
as the current production is still in Post, here’s a simple Ident I did for Animal Planet’s re-branding. Shot on the Phantom. The MeerKat called George, was shot separately in a green screen studio and keyed in. They’re vicious little things…
IT DOESN”T MATTER IF YIU ARE SHOOTING 35MM, RED OR ON A HDSLR i.e. CANON 5D MKII OR 7D. THESE TIPS APPLY TO ALL!
Now enough ALREADY! Give me the TIPS – OK!
TOP TIPS & TRICKS FOR PERFECT GREEN SCREEN (AKA CHROMA KEY)
1) It depends of the size of your Green Screen. Is it a massive sound stage or is it a simple back drop?
Either way the green needs to be even (before lighting). By this I mean, if painted (ideally) the same chroma green paint needs to be used with no stratches or undercoat showing through.
If fabric it need to be stretched so NO creases.
Creases will cause shadows and prevent that area keying well. Make sure you have all the relevant grip kit, stands and clamps to hang it easily to avoid creases.
2) How wide do you intend to shoot?
If you are going to film a wide shot or long shot (head to toe) then you will need green on the floor. A studio with an infinity painted cove is best for this (as you then avoid creases on the floor), but it can be done with drapes if there are no gaps and the fabric has no creases and so no shadows.
3) How big is your space?
You need to be able to keep your talent as far away from the green screen as possible. So when you light them you do not drop their shadows onto the green screen and you keep them away from any green light spill that is reflected/ bounced back from the back drop. Any Green on the skin or clothes will be keyed and look rubbish!
4) What to light first?
Before you even think about lighting the talent you need to light the green screen first. It needs to lit as evenly as possible. I am sure you have heard this before, it’s easier said than done, but how do I do this you ask? If you are using a large studio you should be able to hang the lights from a truss. Space lights are very useful as they provide a very soft even light. You can trace them so they don’t spill light onto your talents head. Other methods are to use larger lights 10K or HMI (corrected to tungsten) through a silk or diffusion frame. The further you can set the lights from the green screen the better as it is easier to keep the same even F Stop on it. This is down to the Inverse Square Law – explained with loads of other TOP TIPS in How To Become a Cameraman
If you are working with a smaller back drop i.e. 12×12 (in the picture above) the best thing to do is use it on a frame. This way it will be tight and not have any creases. Making a ‘goal post’. x2 large stands and a scaffold pole is also a great option. You can also build another one of these to hang lights onto it. For example if your back drop is 12×12, build a goal post with a scaffold pole that is longer and safely rig x3 2K Blondes onto it (I would also recommend having a Grip or member of the Electrical department do this to ensure safely rigged). It is important to use exactly the same power lights on the rig, space them evenly and tilt them evenly. You will also need to add some diffusion this will help soften the light and spread it, it can also help prevent over exposing the green screen.
Once these lights are in position make sure your house lights are OFF and there isn’t any daylight spill into the room then check the light reading of the green screen. You can do this in two ways. One by using a light meter or if you don’t have one a very cool trick and MY TOP TIP is to use your camera as a a light meter. HOW? Zoom into your greenscreen and set your camera expsourer to auto (yes the dreaded AUTO has a purpose after all). Then slowly pan around the green (which will be in frame) and see if the stop changes i.e. F5.6 – F8. Where the stop differs add or subtract more light until it is even. I find you get a good key when the stop is no more than 0.5 (or ideally less) of a stop different. It often involves a little bit of time to get this perfect, but once lit, it is set for the entire shoot. I like to allow a minimum of 1.5 hours to light it, the reality is it can take 2hours to get perfect – I have learnt you have to be meticulous!
Often the lights you hang although the same make and model will not give you exactly the same amount of brightness. This is down to the age of the bulbs. It’s likely you will have to use .3 ND Gel on one or more to balance them. It can also be advisable to half ND the top part of the light. This is because the light closer to the green screen will be brighter. Once again ND .3 usually enough to resolve this.
While we are talking about Gels another TOP TIP I want to share with you is: ‘Always cut ND big enough to double’. This way .3 can quickly become .6 if your estimation is wrong!
Now you are lit from the top, it’s a good idea to fill the green screen from both sides (you can see from the pic above it has been filled from the right side, but not the yet the left – filling really helps). The best way to do this is to use a soft source. A 4ft 4bank Keno Flow is the ideal light. Set one from each side. You can move them back and forwards and add diffusion until the exposer/ F Stop reading is even across the whole green screen (that will be in your frame). If you do not have Keno Flow you can use a hard light source through a diffusion frame.
5) Now my Green Screen is lit – How do I light my talent?
Once you are sure your Green Screen is lit evenly. Double check it! Then if the answer is ‘yes it’s even ok!’, Turn off the lights (yep switch them off) and prepare to light your talent. The illumination of the green screen can be distracting and prevent you from lighting as creatively as you normally would. It’s very important to light for whatever is going to be keyed in the background, having a picture of the actual plate on set is very helpful. As it will help you determine the mood and atmosphere! Just because it is green screen the talent doesn’t have to be lit up like Christmas – imagine how that would look if a dark secret Egyptian tomb was keyed in… Answer = ‘GUFF’!
Move your talent as far away from the green screen as possible. This will prevent unwanted green spill falling into their clothes and skin – which will result in a bad key. Having them away from it will also prevent their shadows falling onto the green when you Key and Fill light them (as in 3 point lighting not Compositing/Keying – confusing?) – as you know any shadows on the green will effect the quality of the key.
6) If you have a green floor, but only shooting a Mid shot
Stand the talent on a black cloth. This will prevent any dreaded green spill bouncing into their face. Simple but effective!
7) Do I need to back light the talent?
YES! However you light your talent you will ALWAYS need to back light them when shooting Green Screen.
It doesn’t need to be a hard glaring back light as you often see, it just needs to add separation from the talent and background.
I like to build a second goal post set up and rig a 4ft 4bank keno in the middle (land scape) and x1 2ft 4bank Keno from either side in portrait to act as a three quarter back light. I then like to mix the bulbs between tungsten and daylight to give the talent seperation from the green screen. If I feel I still need a little more I add a 2ft bank Keno from either side on a shot gun stand/ floor stand. This works as an extra three quarter back light, it is especially useful if the person is wearing dark/ black trousers.
You can of course hard back light them as well, just be careful not to go too overboard if it’s not justified… I have found that the soft light technique can work for most environments and covers the whole spread of the performance space. Having this separation from the green screen is one of the main factors to achieve a good clean key.
8) How do I Key light them?
You can key light (not to be confused with Keying) as you normally would and as the scene demands. Just keep the light off the back drop. If you are in a smaller space this will mean having a high key to prevent dropping their shadow on the backdrop. You then might need to fill light them with a soft source i.e. Keno Flow or Poly (bead board) bounce.
9 ) Under or over expose the Green Back Ground?
People always used to over expose the Green Back ground by about 2-4 stops… I find 4 a little too dramatic and can cause the green to blow out and of course bounce back a lot. I like to keep it no more than max 2 Stops over the talents lighting i.e. if my talents is lit at F4 then the background at a max of F8. There is talk of under exposing the back drop, I have never tried this, but do plan to test it.
10) Tracking Markers do I need them?
If you are moving the camera i.e. tracking then it’s advisable to use tracking markers so in post they can move the background in sync with the camera move. The best way is to make tracking markers is to make a small cross out of camera tape. You can get chroma green camera tape, although some post facilities have requested that I use yellow in the past?… It’s best to try and keep x4 tracking markers in frame at all times – so you need to space them accordingly. Chat to the editor and post house and see what they prefer and if they have specific requirements.
11) Tips for Camera?
Don’t use any soft effects filters or crush the Blacks or Gamma (in the camera menu), it’s best to keep the image as clean as possible. If you require these effects with green screen it’s best they are done in post.
One of the Best TOP TIPS I have is to increase the shutter speed. What I hear you cry ‘increase the shutter speed?’ ‘WHY?’ Well, because most cameras shoot progressive now, there can be a lot of motion blur when you shoot at a regular speed of 1/50 or 1/60. This motion blur does make your footage look more filmic in most situations, but isn’t great when trying to pull a KEY. Increasing the shutter to approx 1/150 decreases this motion blur and helps achieve a better KEY. Motion blur can always be added back in post. I did a big series for BBC where all the action was Green Screen and after tests we found that this method worked incredibly well, especially when the talent did fast hand movements. The one shot when the shutter was set to 1/50 caused complaints from the post department as the definition from the talent wasn’t as good? Crazy I know, but it works! BE WARNED: You need to keep the shutter speed constant and be careful of increasing it too high I would say max 1/150. If it is too high it will give you a Sticatto unnatural feel to the action, which you want to avoid!
12) Will Green work in frame?
What do you think..? Well, due to the advancement of post it is possible to have a different shade of green in shot. I heard about a commercial for a famous fizzy drinks brand that has a green bottle, they were shooting in a green screen studio and at about 11.30am 5 shots down the 1st Ad pipped up ‘does it matter that the bottles Green?’ – both the DP and Director looked at each other…
Personally, I would suggest that it’s probably best to AVOID having any other green in frame – or if something has to be green skip back to the old school and use Chroma Blue…
All in all the best way to get perfect green screen is to do some tests for yourself, then sit in on the post production process – see what does and doesn’t work and why! Yep cross over to the ‘other side’ make friends with some Editors, order Lattes, Sushi and eat loads of biscuits together! You both might learn something…
I feel a little like the Masked Magician, only without the gimp mask, glamourous assistants and the Magic Circle on my Ass…
Good Luck and Enjoy!
PS If you like these Tip there’s loads more in my books I have just (delved deep into brain) written took ages… so many cups of Tea…
Plus, if your too tight to buy it there loads of FREE TIPS to download too!