Chroma Key, better known as blue or green screen, is a great way to immerse the viewer. With still images, it is easy to “cut” out individual images and paste them into new scenes using using your standard Photoshop editing tools. With video, this would be too tedious as there are too many frames to edit in this fashion. By having a well lit background screen with a uniform color behind the subject, it is easy later for software to identify subjects, and separate them from the background. Once the foreground subjects are isolated, the video can be combined with other stills or video to create scenes that would be impossible to capture otherwise.
The following Van Halen Panama cover was produced using a Floyd Rose Discovery series guitar, a Digitech RP350, two Sony DCR-SR100s, one Karaoke machine, VirtualDub, Adobe After Effects, a green screen and plethora of halogen lamps. The background image was taken with a Nikon D300 in Muir Woods, California in 2008. A Sony DCR-SR100 video camera was first mounted on the Floyd Rose guitar and pointed towards the halogen lit green screen. The trick here is to place strong lights in such a way as to avoid any shadows on the background screen. Subjects should not wear clothing with coloring similar to the chosen background Chroma Key color.
At this point, the video’s audio channel output was combined with the stereo guitar output (using the Digitech RP350 processor) and the backing track using a karaoke machine. The video and stereo outputs were multiplexed using a duplicate video camera which produced the interlaced NTSC Mpeg video file. The VirtualDub software was used to create a deinterlaced AVI from the MPG source. Finally, the Adobe After Effects software combined the still and the movie data using the Chroma-Key technique and added interesting elements like rain and sound keying through the use of layers and masks. The rain droplet size was sound keyed to the music. The final video was rescaled and compressed for use on the web.
This Chroma Key video below demonstrates the superimposing of a single video onto a still background. Artificial rain is introduced using Adobe After Effects, and the raindrop sizes are tied to the music’s sound amplitude. The next Chroma-Key video goes one step further.