Film Projects

Blue or Greenscreen

Aka. chroma key, and color keying.

YUV color space [1]:

• Y: Luma - Brightness black-and-white signal
• UV: Chrominance (blue and red components) - Color signal

YUV is not an absolute color spacem, it's a way of encoding RGB information [2].

Chroma resolution [3]:

• 4:4:4 (Y:U:V) - full resolution / high bandwidth
• 4:2:0 (Y:U:V) - less color resolution / lower bandwidth
• 4:1:1 (Y:U:V) - less color resolution / lower bandwidth

MacBreak part 2 explains and shows how chroma subsampling works.

The green information is usually preserved in the Y channel [4]. Which makes a green background perfect because of the extra channel resolution on 4:2:0 and 4:1:1 based cameras. In addition green is not a color usually found on a human being, making it easy to key.

Quotes:

If you can plan your DV shot to have mostly dark subjects (dark hair & clothing) in front 
of a green screen (or bright/blond subjects in front of blue), you can use the color difference 
key to pull a quick core matte, then turn to a luma-based solution to bring out the edge details.

With DV and DVCam, you won't have as much color information per pixel due to compression, so 
good mattes are harder to pull. It ends up looking pretty aliased. Both NTSC and Pal DV formats 
have pretty low sampling (4:1:1 for NTSC and 4:2:0 for Pal).

It was all pixelated and jagged edges. How do u get around this?
The technique that I've heard used most often is that you blur the UV channels (the chromanance 
part of the YUV) then mix that back in with the Y (luminance) and your ready to pull a matte. Do 
just enough blur so the pixelated jagged edges soften. Use that only for pulling the matte. Once 
you've got your matte, go back and use the original footage for applying the matte.

• CGTalk GreenScreen
• PCQuest Matte creation in After Effects
• dvGarage dv Matte Pro
• DVCreators Green Screen!
• MacRumors Bluescreen on the cheap?
• Bluescreen on a budget
• Tips for compositing DVC Pro HD footage
• Making Light Of The Matter
• MacBreak HD green screen shooting part 1 - setup
• MacBreak HD green screen shooting part 2 - resolutions and color compression
• Wikipedia Chroma subsampling
• Chroma key Wikiepedia Chroma key (Bluescreen)

Programs / Plug-ins

• dvMattePro
• Keylight
• Shake (OS X only)
• Final Cut Pro (OS X only)

Lightning

• Soft Lightning
• PhotoFlex / PhotoFlex Equipment Lessons