Chroma Key Live (v08-12-16)

Dec 16, 2008, by ZLP

IMPORTANT!!! ---- Check for updates: http://www.zachpoff.com

Summary:

Chroma Key Live is a free software tool to view a chroma key (AKA "green screen") in realtime during a video shoot. In the days of analog video, the camera's live signal was routed through a keyer in the control room and delivered back to an on-set monitor. This way, the production team could see exactly how the actor looked when composited over the background image. (TV weather people use this image to locate their hands over the virtual maps behind them.)  Modern digital video is shot without the support of an analog studio, so the chroma key is created afterwards inside the computer. This leads to a problem: How do you visualize the composited image on-set when all you can see is the actor against a green screen?

Now it's simple: Run the firewire output from your camera into a laptop running Chroma Key Live. Click on the live video image to choose your key color and load a Quicktime background file (movie or still image). Now you can see your actor composited on top of your background! (Note: Chroma Key Live cannot record. It is strictly for on-set preview. You can do much better keys in post-production software.)

Chroma Key Live gives you control over key tolerance and edge fade, and offers features like full-screen mode, title/action safe guides, image-flip (so your actors don't see themselves backwards), and a useful "transport" so you can control the playback of your background videos. There are several keyboard shortcuts and both NTSC and PAL formats are supported. (It also works with the built-in cameras in Apple computers and any UVC compliant web cam.)

Background File Preparation:

You want the composite in Chroma Key Live to be reasonably similar to the final post-production version. Chroma Key Live will scale your background image to match the current video dimensions (either NTSC 720x480 or PAL 720x576). So it's best to prepare your backgrounds to match these dimensions. Later in your post-production software you will be able to load your backgrounds and achieve a familiar spatial match between your actors and your backgrounds, with no arbitrary scaling.

Like most editing software, the Chroma Key Live transport uses the J,K and L keys for backwards, pause, and forwards. You can also hit the spacebar anytime to play your video clip from the beginning. This is useful for cues where the actor needs to hit a mark on the background movie.

Preferences:

All settings are saved automatically to an xml preferences file whenever you close Chroma Key Live. If you want to get really nerdy, you can edit the xml with any text editor (but Chroma Key Live doesn't monitor changes in the xml while it's running). 

License:

Chroma Key Live (and its "source code" MAX/MSP/Jitter patch) is released under a Creative Commons Attribution-Noncommercial-Share Alike license, which means that you are free to modify and redistribute it (with attribution) provided that all derivative products remain non-commercial. (see http://creativecommons.org/licenses/by-nc-sa/3.0) It was developed in the MAX/MSP/Jitter visual programming environment ( http://www.cycling74.com ) which will be required if you want to edit the source code. ($$$)

Change Log:

Version 08-12-16 (Dec 16, 2008)

First Release