Working with Green Screen (and avoiding a nervous breakdown in the process).

As someone who was once a media student, I understand wholeheartedly how panic-inducing working with green screen is if you don't understand precisely how it works. During filming, it may appear to be fine, why it may even be fun - but whoever is in charge of post production will swiftly place a bounty on your head if you present them with footage that appears to have a lighting set designed by a sleep-deprived baboon If you happen to be editing footage like this, nobody who has ever been in that situation would judge you for crying.

Firstly, lighting is crucial to a successful green screen film. Crucial. I truly cannot emphasize enough that an inexperienced lighting technician looking to experiment should not be taking risks with the lighting on a green screen set!  While using green screen, a 5 point light set up is ideal. You will need to have enough light to light up the backdrop completely, as well as the character. If there is not enough light on the backdrop, shadows or hot spots will appear, which are difficult to key out during the editing process. If your character is not lit well enough, they will actually start to disappear into the background once the editor begins keying, because there is not enough definition between the character and the green screen. 

 While working with a green screen, to be safe,  it advisable to aim to have a 5 point light set up if possible, in order to get the most “key-friendly” footage. In post production, poorly lit green screen could lead to your actor disappearing into the background, the foreground being grainy or under-exposed, and being faced with a giant shadow that just won’t key out. I have learned from experience that disappearing characters and obnoxious shadows can turn a once peaceful human being into the Incredible Hulk, cursing obscenities at Final Cut Pro before running screaming into the night to find that "(expletive) lighting technician".

The most basic way to appropriately use this 5 point lighting system is to keep the key, fill, and backlight in relatively the same position as you would have them in a 3 point lighting set up. With the key being the brightest light, position it at about a 45 degree angle from the camera, facing the character. The fill should be on the opposite side, at a lower intensity, and still at that 45 degree angle from the camera. The backlight can be positioned behind and slightly to one side of the character, so it frames the subject and is out of the camera’s view. The other two lights you can use to light the backdrop. Placing one on either side, but letting the beams cross each other so that the light seems to just flood the background.

If you have a character that is lit perfectly with 3 lights, then a three point lighting system may be all that is required. However, the more characters in the shot, the more lights needed. That is basic green screen algebra - More Characters = more lights. The wider the shot, the more light needed. If you decide to create any sort of mood lighting, or emphasize certain props or aspects in the shot, the more lights you shall need. 

Notice how "LIGHTS" comes first...

Three point lighting is a technique used in various forms of media. Used in film, photography and even CGI imagery, this technique has become a standard practice in many sections of media production. The name "three point lighting" comes from the fact that while using this technique, the media maker will place three seperate lights in three seperate positions, in relation to the character being filmed or photographed. This means that the character on screen can be illuminated, however desired. It also means that the shadows within the shot can be controlled by placing the lights in the appropriate direction.

Out of the three lights used in this technique, the key light is usually the most important light that a cinematographer will use during this lighting set up. There are different ways to optimize the use of a key light, but while using three point lighting, it is positioned at a 30–60° angle, the beam directly reaching the character being filmed, and acts as the main source of light for the shot. The key light dictates the lighting design, which we will keep in mind during filming, as we will need to take into account the strength, angle and colour of this light as it effects the entire aesthetic of the shot. You want the key light to illuminate the actor in a way that eliminates shadow and works well with the other two lights to create even lighting, a crucial element in a successful green screen production. Which I am quite sure I have mentioned.

When God said "Let there be light"...he meant for green screen.

The fill light in the three point lighting system, is used for the purpose of decreasing the contrast of the scene, and to decrease the strength of the shadows within the frame. The fill light is usually softer than the key light, but the ratio between light and shadow depends on the intent the film maker has for the scene. It is placed at a side angle to the key light, often below it, at the level of the subject's face - this will be important to master for your green screen so that you can illuminate the subject appropriately in order to make them correspond with the back plate.

The last light included in three point lighting, is the back light. This is placed behind the character, again, to correspond with the image on the back plate (for instance, if it is a cold, blue light, we will use an appropriate filter on the back light to give this impression).

It is a common misconception that when using green screen, to get the best result it is wise to shine as much light at the green fabric. This is certainly not the case - the most important part of getting a successful green screen shot, is how the subject in front of the green screen is lit, and how consistent that light is with the back plate. The film, Sin City, is an excellent example of how to use lighting when using chroma key. And a good film to boot.

A good use of green screen.

 When using green screen it is very important to check what lights or light sources are present in the image that are scheduled to be placed upon the back plate in post-production. Far away lights in shot, (for example, lamp posts if the character is meant to be walking down the street at night), will give the scene a hard back light, whereas nearer lights such as a lamp post the character is standing under, will illuminate the character more rather than the back ground. All light sources in the image to be placed around the character using green screen must be taken into consideration in order to provide consistent lighting for the shot in the studio.

Oh editors...my heart goes out to you.

  A good way to understand how the lighting is going to be effecting the subject in question, is to have a member of the crew hold their fist in the air, (have someone put Van Halen on to pump your fist to if you feel silly doing it in silence) while blocking out light with the other where the character shall be standing. This blocks off one light in order to see how the light from all the other angles are effecting it. Once the shots have been decided, and how the subject is going to interact with the background, it is important to ensure that the subject being filmed does not go off the edge of the green screen. Remember - if the subject goes off the edge of the screen, the editor will go over the edge in post production. And we love our long suffering editors.

The most even light possible, with as little shadow as possible, is what should be aimed for when working with green screen. You should try, if possible, to make sure that the lights in your production are behind the subject, to ensure that they create as little shadow as possible on the back plate. Because of their flexibility and powerful beams, dedo lights are ideal for using when working with green screen. The power of the beams are adjustable, and they are mutli-directional. However, be weary of barn doors possibly creating patterns on the green screen, and potential hot spots from the powerful beam.

Once the lights have been set up and switched on, it is advisable to take photographs of a subject in front of the back plate, run the photos through photoshop and turn the contrast of the image down. This will allow the crew to see any dark areas or hotspots that are in need of correction in the set up, that may not be visible by eye. This saved us a lot of time and stress when I insisted on doing this to my crew for our first green screen project.

If you do not have a lot of distance in the studio, some lamps may be too big for your production, the beam too powerful. Especially if you are media students, trying to keep the rest of the class at bay as everyone is waiting their turn to use the studio due to booking the studio at the very last minute. I understand, there were parties I simply couldn't miss out on either. When I was a student, we were very limited to the kinds of lights we had access to, but there are ways around this if the lights we booked proved to be too powerful. 

Tough Spuns: WORTH GOOGLING.

 

Tough spuns for example are not that expensive, are fire proof and brings the level of the beam down when placed with the lamp. Tough spuns come in degrees of transparency, from full to 1/4. Although we may be using powerful lights they are not only adjustable, but if they still prove to be powerful, we can always put filters on to accommodate the shot we want. Believe me, if you are making a green screen film, tough spuns are certainly worth Googling and may earn you several drinks from your crew when they save the lighting for your project.

Once the green screen has been appropriately lit, it will be possible to appropriately light a subject. The background plate will have to be taken heavily into consideration, and lights close to the subject will have to be placed roughly at the same height and distance from the subject as they would on the back plate.

If you will shoot your own footage for the back plate, you will need to take photos and footage of the location, in order to get consistent lighting. If you plan to use a template that is not your own, you will have more freedom to experiment with the lighting - however, common sense about where the light would be coming from in the image is vital. You could not, for example, have light obviously and intrusively beaming up from the floor if your subject is walking on a woodland path. Unless the plot involves a frolicking Dorothy Gale on the beaming yellow brick road. And even then you would be lucky to justify light beaming from the very floor.

Colour Temperature: Blue.

 The colour of the lighting is also important to take notice of when observing the image due to be placed over the green screen. For example, if the subject is meant to be walking on a modern pier at night, while there may be lighting in the form of lampposts, it will need to be a cool light, so a CTB (colour temperature blue) gel may be placed over the light, in order to create the appropriate back light for the head and shoulders of the subject, while mimicking the lights that would be present on the pier.

Light Reflector: A media student savior.

Another tool that is useful when working with green screen is a reflector. It is used to even out harsh shadows and give fill to the subject where needed.

...I hope to God I'm pointing at England.

Although lighting is paramount (as you have probably guessed from this blog....) to the success of a green screen production, there are other things to take into consideration, such as how convincing it is that the subject is indeed at the location fitted over the green screen.

Youtube is full of clips making fun of the terrible use of chroma key in the 70's and 80's, where a weather man would perhaps point to Scotland and cheerily chirp about how sunny England was going to be on Tuesday. Or unknowingly dipping his hand into the Atlantic Ocean when consoling Ireland about the rain they were due to receive at the weekend.  That is not how you want your project to be remembered, graded or reviewed.

  

Tips to avoid embarrassment of this nature: If the location is windy, a fan may could used to create the effect of wind blowing through a subject. If the shot includes rain, it may be wise to put droplets of water on the subject's costume and hair (you will of course have to be careful if this is the case, being surrounded by so much electricity in a studio!). If there is action in the background, it may be worth experimenting with crew members waving their hands past the lights to correspond with the background. 

 Because I understand how frustrating chroma key can be to work with, I have some further short tips for you young film makers out there:

 

. Make sure a storyboard is in place so that the entire group knows what the aim of the project is, and what the background is supposed to look like.

. Use a shallow depth of field in order to control light spill.

. Avoid the characters on set having green clothes while working with green screen. Or blue clothing when working on blue screen...I am sure you can see where I am going with this.

. In regards to props, avoid shiny ones. Shiny props might reflect the green of the screens and give the characters a sickly look and the set a sickly hue.

. You cannot fix the lighting in post production when working with green screen, this is NOT the project for inexperienced lighting technicians to experiment and gain more experience! The light must be even and bright on every portion of the green screen material.

. The actual green screen itself must be taut and unwrinkled, in order to get the best possible results. If there are imperfections on the screen itself they will show up on the footage.

. Never place your subject right next to the screen. Move your subject as far away from the screen as possible.

Green Screen users of the future: I wish you luck and truly hope my article helped! 

Adieu. 

Louise.