Blue Screen

[Roger]

Hi,

I have little experience in photography or filming.
However, a friend and I would like to make a multimedia CD (just for fun)
and we would like to render background images and then place filmfootage and
photo's of ourselves on top of it. I know that by using a blue screen (or
green screen) one can do this.
What I wish to know is:
1. Do you need to use a specific blue/green?
2. Special lightning
3. Particular clothing (colours)?
4. Anything else... ?

Maybe someone knows of a site where these questions are answered.
I looked for sites myself but couldn't find the necessary answers.
(Maybe I'm just using the wrong keywords. Yes I tried blue and green screen
:) ).

Thanks,

Roger

[GTMO DIVER]

Roger wrote;

Blue screen film technique is pretty complicated. It does require the
backround to be a particular shade of blue because it then uses orthochromatic
film to make separation negatives of the blue area.
It also generally takes a good bit of hand retouching of the different
separation negs to get good edges and eliminate areas of unwanted show
through.
You then have to make separation positives from the separation negatives and do
the same retouching to clean them up.
Then you print with a least two exposures (more if you want more than one
superimposition on the print). First you take your backround scene negative in
a sandwich with the separation positive and expose your paper. Then you take
your super subject negative in a sandwich with the separation negative and
expose the paper with it.
It involves several steps, a good deal of artistic skill and careful alignment
of the several negatives to get a decent result.
I would avoid it if you don't want a final product on photograhic paper.

Video blue screen or green screen more correctly called "Chroma Key" Is a lot
easier but requires special equipment, A genlock which synchronises the
mulitple video feeds and a chromakey switcher which superimposes the to video
feeds based based on the color you've chosen to separate them.
Your can then pick any color you want to key from but generally blue or green
is used because it doesn't show up in skin tones.
Clothes and lighting are important.
The blue background must be evenly lit because uneven light or shadows may
cause the switcher to see it as something other than the key color and not let
your super shot show in those areas.
Any where your key color shows will let your super shot show through. Whether
it's from light of the key color shining on your subject or clothing prints
which have the key color in them.
Lots of fun, easy to do. There are plenty of books and magazines out there
dedicated to amateur video production which will explain the details and
equipment more thoroughly.
-Greg

P.S.
This actually had a neat if unexpected affect on my son recently.
The local PBS station had a blue screen set up at a fair we went to. They
would put kids in front of the screen and let them be "weathermen" by supering
them over different maps and forecast screens.
My son stepped up and he was wearing a blue shirt with green lightning bugs all
over it.
Well, the shirt was close enough to the key color to disappear, and there was
my son's disembodied head on the television screen floating above a swarm of
fireflies. It was hilarious.

[Michael J Edelman]

Darrell A. Larose wrote:

> I believe the TV/Movie term for "Blue Screen" is chromascreen.

"Chroma key"