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Posted by nobody special on 04/17/07 23:29
Quick and cheap way to measure without scopes: use the zebra bar
setting in your camera. If you have controls for setting where the
zebra bar display is triggered, you can set that and look in your
viewfinder to see if the zebras cover the whole screen evenly edge to
edge at the set level. Better yet, if your camera can show two sets of
zebras: make one trigger at around 60 IRE, the other for peak whites
at ninety. Check your manual.
If you are doing these chrmakeys live thru a switcher, try this: make
a wipe between the green screen picture from the camera and a
grayscale chart you can make in photoshop, or just some grayscale
swatches or boxes made using whatever you have for a CG/titler. Use
the "blue gun" button on the TV monitor, or if you don't have that,
turn all the color down on the monitor so it looks black and white,
now eyeball the relative brightness of the half-image of your green
screen versus the sample blocks image. Adjust the manual iris on the
camera until the greenscreen alone is just a little brighter than the
halfway level of your grayscale, dig? Your auto-iris is getting
freaked out and fooled by the greenscreen, and this messe with your
overall exposure and makes you waste extra power and light in over-
lighting the parts that don't need it so much.
You light the screen by itself first, then bring in the actor and
light them separately, without touching that pre-set iris opening,
until the actor is also well-exposed with good-looking contrast. You
need at least six feet of dead space between the green and the actor.
Now you are in the ballpark at least.
If you do the keying in a nonlinear editing program, many of these now
have virtual scopes you can bring up to see the levels. If you make
some notes on your iris settings that correspond with the scopes, you
can create a "recipe" for doing better next time with what you've
got.
Best of luck, let me know if this helped.
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