Difference between revisions of "Film Projects"

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== Blue or Green-screen ==
== Blue or Greenscreen ==


<small>Aka. chroma key, and color keying.</small>
<small>Aka. chroma key, and color keying.</small>

Revision as of 15:14, 6 April 2008

Blue or Greenscreen

Aka. chroma key, and color keying.

YUV color space

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

Chroma subsampling resolution

  • 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.

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.

Programs / Plug-ins

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

Lightning

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