Re: Green wall vs Blue wall
> Some stations like WTNH use blue and other like WVIT use
> green. Why?
Any solid color will work to produce chroma keys. A fairly dark
blue produces good results but the shade of blue is very important.
There's a lot of blue clothing around and a fair number of people
have blue eyes. If you don't keep the shades differentiated you
can end up with some weird results. Also, there's essentially
no blue content in flesh tones (except if the news is exceptionally
dead that night).
Since green produces equally results it's pretty much the choice
of the producers/directors/engineers, etc. at any given station.
Maybe anchors are partial to blue clothing; that would drive the
choice toward green. There's essentially no blue in flesh tones
unless the news is especially nauseating that night.
The choice is driven by preference at the local station.
So what IS chroma key?
A technique whereby, in a video switcher, one exact shade of a
single color is selected. A mask is generated which includes all
of the picture of that color. The mask is turned into a "key"
signal which has no shades or colors; it's all at one very high
video level. That signal is used to switch between two sources.
For example, run a tape of a crowd and the key signal. line by
line, will switch the output video between the crowd scene and
the object (typically a person) which does NOT include the
chosen color. When the line reaches a point in the video where
the selected color does appear it causes a switch back to the
crowd. At one time the quality of the "switch" was pretty bad
and you could see a visible "fringe" around the object. Next
step allowed the object to cast what appeared to be a shadow
on the inserted background. There were expensive devices that
did not use the video internal to the switcher to generate
the effect, rather used the RGB (Red, Green, Blue), signals
directly out of the camera to produce it. Now with lots of
stations using digital switchers, fringing is almost entirely
a non-issue.
BTW....If somebody wanted to play around, you could have a blue
(or green) wall used to generate the key and, instead of using
something off tape or film to produce the "background" signal you
could use a color background generator and turn the blue (or green)
wall into any color you choose! There was this one young female
newsette (PC didn't exist then) who preferred a soft pink
background.....
Back in the day I was party to a series of very-late-night newscasts
that were a spoof of lots that went on in "real" news. Anchor's
names were sometimes intentionally misspelled and, every now and
again, a tight shot on the anchor would use chroma key to rip
the blue out of his eyes and substitute flames off a film. But
only when he was flamingly passionate about a particular story.
Then, as the story ended, the key would be mixed out.
OK, Mr. Gallant...gonna spill the beans on what station that was?
<P ID="signature">______________
Fanatics are picturesque, mankind would rather see gestures than listen to reasons.
--Friedrich Nietzsche</P>
