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 Author Thread: A way to improve chroma key....
dlk is not online. Last active: 7/2/2011 1:14:29 PM dlk
Top 25 Poster
Joined: 11 Sep 2004
Total Posts: 2027
 
A way to improve chroma key....
Posted: 11 Nov 2004 12:11 AM
I think I have found a way to at least improve a few
applications of chroma key. For me at least.
Because chroma key seems to be often
requested, and often discussed...let me
clarify the uses that I understand.

1) Green screen or blue screen.
This is where you photograph(videotape) someone
or something in front of a solid colored background
such as a green or blue screen. During the edit procees,
you merge this photo(film) with a new backrground
such as a London bus, eliminate the green or blue,
and ta da...you are a world traveler.
Tricky business....you may need a special screen,
not sure you can make your own, not sure digital
camcorders can do this very well...not sure MM2
is the right editor...some high priced programs
do it. It would be fun...but I am not optimistic


Now...more realistic stuff

2)Animated GIFS and image overlays.
These work fine for me, except for the
size of the animated GIF. If I try to
add a animated butterfly going across
the video...I get a monster butterfly.
Not the effect I wanted.
But if you have problems...perhaps
your background isn't the color you think
I use PNG files and black backgrounds, so
my chromakey is 255,255,255.


3) PIP effects moving across the screen.
I picked this up from PapaJohn. I take a black
background, transition it with the clip I want
using PIP...and save that movie. Now take
that movie, use the panzoom effect to move
the PIP window across the screen, and then
use the chroma key transition to overlay
the moving PIP clip onto another clip. The
problem is that when I save the PIP movie,
the black background changes color. Instead
of 255,255,255...it is 253,253,253.
My chromakey doesn't work. So...I could change
my XML file...but I don't think it's always the
same. So ...I realized I can decrease brightness
on my clip...just a little. That brings my
background back down to 255,255,255,
but doesn't really hurt the clip.
It also gets rid of bleeding around the
edge of the PIP window...makes a nice
crisp edge. You might also try this
on your animated GIFs....
Here is the brightness effect....also a small
increase effect.....if you wish to use a white
background instead of black...

<EffectDLL guid="{5A20FD6F-F8FE-4a22-9EE7-307D72D09E6E}">
<Effect name="Whiten" iconid="7" comment="Brightness increase">
<Param name="Brightness" value="4" />
</Effect>
<Effect name="Darken" iconid="6" comment="Brightness decrease">
<Param name="Brightness" value="-4" />
</Effect>
</EffectDLL>


I hope this makes some sense.

dlk








dlk is not online. Last active: 7/2/2011 1:14:29 PM dlk
Top 25 Poster
Joined: 11 Sep 2004
Total Posts: 2027
 
Re: A way to improve chroma key....
Posted: 11 Nov 2004 07:14 PM
Ooops...
Obviously 255,255,255 is white and 0,0,0 is black. The idea
is the same though. Chroma key doesn't work if the colors
are off by even the smallest amount You can use the
brightness transitions to take them to the max.

dlk
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