Chromakeying on Casablanca
ChromaKey is a process where a color
(usually blue or green) is digitally subtracted from a video scene,
allowing a second video scene to be inserted in its place. On Casablanca you use the 'BlueBox' found under the 'Special' button in the Edit screen.
This software effect is included as part of the Operating System (some early versions required the activation of BlueBox after you registered your Casablanca - if this is your case, please contact your Casablana reseller for assistance).
Let's
walk through the process using the following two scenes ‘Actor' -
a hypothetical scene of an actor in front of an evenly lit, uniformly
colored background (blue and green with 50% color saturation work
best).
The 2nd scene, Jelli is a scene from an aquarium
with Jelli swimming around in a tank. The desired effect is to have
the Actor appear as if he is in the tank with the Jelli.
In the Edit Window:
- Trim the clip 'Actor' to :04 seconds long .
- Trim the clip 'Jelli' to :04 seconds long. (This is important IF you wish
your Chromakey (Bluebox) to be a combined shot during the entire
effect).
- Add the clip Jelli' to the
storyboard (the clip you want to have as the 'base' scene).
- Then add the clip 'Actor' on the storyboard (the shot with your talent)
- Select Bluebox and insert into the
storyboard - making sure the two scenes above are in the Workbox.
- Set the transition time by
clicking on‘X s' set this to the entire length of the clips
(easy to do, just slide all the way to the right), click OK.
- I prefer to do most of my work in
BlueBox, BlueBox World, PIP Studio, etc. using the Full Size preview
screen - to do this, click on ‘Full Size' beneath the
Storyboard.(make sure ‘Display'is set to
‘Effect'
- Click on Color Choice,
- Click on ‘Size' and move
trackball around until sample box (dashed lines) are small enough to
sample or select the color you are going to key out (cut out). Left
click Then you can use ‘Position' to move that sampling box to
wherever on screen is the best spot to grab a sample of the
background color NOTE: make certain that you only
have your background color in this sample box - any other colors
and your effect will not be clean or successful.
- Click Size, then scroll trackball
until the box is small . Click again to set.
- Left click ‘ok' to exit the
sample box menu
- Left click on the slider in ‘Color
span' - this will fine tune the key effect. In general I find
the best results occur in the high 80s and low 90s.
You may also choose to set Include
Area and/or Exclude Area. If you wish to have the effect on the
whole scene, insure the Include Area has the whole scene included
and the Exclude area has none of the scene selected.
Experiment to set Color Range to a
percentage that gives the best result. Click again. Repeat until
you've found a value that gives a clean result, with no
raggedness. Then left click OK.
You can also run a Preview to see
motion.
Then click on Create to render
your Bluebox effect. You could also make a scene of the result.
This would insure you have this available as a clip in your clip bin
with the effect permanently complete.
**The most technical aspect of using
the Blue Box effect is setting the Color Range slider. By adjusting
this setting, you are determining the tolerance for the color that is
being keyed out (which, in my example, is green). If the percentage
is too low, you will see green shadows and edges around the Actor's
body. If the percentage is too high, parts of our Jellifish will
become transparent. There really is no ideal or recommended setting
for this option; you'll need to experiment with it on your own in
order to become familiar with its range.
Also - this effect will only be truly
successful when using a scene with optimum background coloring. Even
using a commercial Blue or Green screen will not provide great
results unless it is lit evenly. If there are ‘hotspots' from
inconsistent lighting that will affect your results (and not in a
good way).
For greater control and more sophisticated chroma key operations, check out BlueBox World and the Keyer functions in CB Paint/CB Paint 2.
