[Guide] How to use chroma keying (greenscreen) in SFM

Despite the fact that there are a number of maps out there that can be used in SFM, it is still sorely lacking in the map department. One of the ways to overcome this is to pick a generic map and scene build it to suit your needs, but sometimes this just isn't enough.
There IS an alternative.., you can use either a green or blue screen and insert an image behind your scene to enhance it.

Before you go off 'half-♥♥♥♥♥♥' here, you cannot do ALL of this from within SFM, but you can do most of it in SFM, and I'm going to show you how...

Some background on the green/blue screen effect...

Greenscreening, a.k.a. chroma keying, has been around for a long time, but not everyone knows what it is, or even how to do it, so here's a little background to get you up to speed on what it is and how it works.

Greenscreen

Chroma key compositing, or chroma keying, is a visual effects/post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate the color used as the backing.

It is commonly used for weather forecast broadcasts, wherein a news presenter is usually seen standing in front of a large CGI map during live television newscasts, though in actuality it is a large blue or green background. When using a blue screen, different weather maps are added on the parts of the image where the color is blue. If the news presenter wears blue clothes, his or her clothes will also be replaced with the background video. Chroma keying is also common in the entertainment industry for visual effects in movies and video games.

Bluescreen

The blue screen method was developed in the 1930s at RKO Radio Pictures. At RKO, Linwood Dunn used an early version of the travelling matte to create "wipes" – where there were transitions like a windshield wiper in films such as Flying Down to Rio (1933). Credited to Larry Butler, a scene featuring a genie escaping from a bottle was the first use of a proper bluescreen process to create a traveling matte for The Thief of Bagdad (1940), which won the Academy Award for Best Special Effects that year. In 1950, Warner Brothers employee and ex-Kodak researcher Arthur Widmer began working on an ultraviolet travelling matte process. He also began developing bluescreen techniques: one of the first films to use them was the 1958 adaptation of the Ernest Hemingway novella, The Old Man and the Sea, starring Spencer Tracy.

Petro Vlahos was awarded an Academy Award for his refinement of these techniques in 1964. His technique exploits the fact that most objects in real-world scenes have a color whose blue-color component is similar in intensity to their green-color component. Zbigniew Rybczyński also contributed to bluescreen technology. An optical printer with two projectors, a film camera and a 'beam splitter', was used to combine the actor in front of a blue screen together with the background footage, one frame at a time. In the early 1970s, American and British television networks began using green backdrops instead of blue for their newscasts. During the 1980s, minicomputers were used to control the optical printer. For the film The Empire Strikes Back, Richard Edlund created a 'quad optical printer' that accelerated the process considerably and saved money. He received a special Academy Award for his innovation.

For decades, travelling matte shots had to be done "locked-down", so that neither the matted subject nor the background could shift their camera perspective at all. Later, computer-timed, motion-control cameras alleviated this problem, as both the foreground and background could be filmed with the same camera moves.

Meteorologists on television often use a field monitor, to the side of the screen, to see where they are putting their hands against the background images. A newer technique is to project a faint image onto the screen.

Some films make heavy use of chroma key to add backgrounds that are constructed entirely using computer-generated imagery (CGI). Performances from different takes can be composited together, which allows actors to be filmed separately and then placed together in the same scene. Chroma key allows performers to appear to be in any location without leaving the studio. Computer development also made it easier to incorporate motion into composited shots, even when using handheld cameras. Reference-points can be placed onto the colored background (usually as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall). In post-production, a computer can use the references to compute the camera's position and thus render an image that matches the perspective and movement of the foreground perfectly. Modern advances in software and computational power have eliminated the need to accurately place the markers – the software figures out their position in space (a disadvantage of this is that it requires a large camera movement, possibly encouraging modern film techniques where the camera is always in motion).

Source: https://en.wikipedia.org/wiki/Chroma_key

Some samples...

Here are a couple of examples of completed chroma keyed images:

This one was done with a greenscreen:
https://steamcommunity.com/sharedfiles/filedetails/?id=813721219
Greenscreen is most commonly used with brighter lit scenes.

This one was done with a bluescreen:
https://steamcommunity.com/sharedfiles/filedetails/?id=1095487876
Bluescreen is most commonly used for darker scenes.
(Think scifi movies like Star Trek's space battles where the background is usually the blackness of space.)

The two screens can also be used together for even more compositing fun, but we can discuss that part later...

What you will need to do chroma keying...

Obviously, you will need to have Source Filmmaker installed and working, that's a given, but you'll also need some image or video editing software to make the actual magic happen when it comes to chroma keying.

It's been my experience (10+ yrs as a video editor) that video editing software does chroma keying the best, afterall, the technique was developed specifically for video in the first place.
Here are some free video editors that should do the trick:

• OpenShot[www.openshot.org] (Free)
  
• ShotCut[shotcut.org] (Free)
  
• VirtualDub[www.virtualdub.org] (Free)

I'm sure that there are others out there, these were just the ones that I'm aware of...

If you aren't 'allergic' to shelling out some 'big bucks', then these are definitely the way to go:

• Adobe Premiere Pro[www.adobe.com] (I use this one)
  
• Sony Vegas[www.vegascreativesoftware.com]

Video editing software is not the only thing that you can use to do chroma keying, you can also use image editing software to do it.
Here are some options, depending on your budget:

• GIMP[www.gimp.org] (Free)
  
• Adobe Photoshop[www.adobe.com] (This is the one that I use)

This is a pretty good tutorial on how to do chroma keying in Photoshop:
https://photographysandbox.wordpress.com/2015/01/19/remove-green-screen-photoshop/

Here's one for GIMP:
http://www.diaryofatechiechick.com/2013/04/removing-green-screen-as-easy-as-1-2-3.html

Anything Else?

Well, as a matter of fact, yes, you will need one other thing to make this happen.
Luckily, it's on the SFM workshop...
https://steamcommunity.com/sharedfiles/filedetails/?id=186065555
I use these myself and they are very handy for lots of things due to the fact that they come in several colors, including chroma key green and chroma key blue.

Due to the length of the subject, I will be showing how to do the actual work in a video using Adobe Premiere Pro CS6...

The video...

If you have any questions or comments, you know what to do...

[Pizza Man]

Another tip I think you forgot is to make sure you turn the Bloomscale on your cameras to 0. That bloom is a pain in the ass to chop out when you have a green screen, and SFM bloom is just bad to begin with.

[Capt Fuzzy]

You're welcome!

[Blueber_y]

Thank you

[Capt Fuzzy]

I've not tried this with Blender, but since it does have a 'video editor' built in, I would think that it's possible...

[76561198239167412]

*wonders if I can do this with Blender and wonders how easy it is with Blender*