#Rendering
9 messages in this thread
I need some help concerning layering an animation over live video. My
editingpeople tell me I need to render over negative black (-5,-5,-5) so that
the animation will key over the video cleanly. As far as I can tell, my black
background is 0,0,0 and on the scope its +5,+5,+5. Would this suffice for a
clean overlay?
Thanks,
JC
Jim,
For a clean overlay over video you want to use a mask. 3DS provides you with
this by allowing you to "split-alpha". When you render you will get two files
per image. One is what you want to key over the video, the other is a white key
or hole cutter for a luminance key. You need to off these images to two
seperate tapes, then use the white mask as the hole cutter and you can fill
that with your rendered image. If this sounds greek to you, relay this to your
editor, he will understand.
What you need to know is that, you want to render in fields, and also want to
use split alpha. Then put the two renderings to seperate tapes. The editor can
handle it from there.
The reason this is the best method is that it doesn't restrict you from using
dark areas in your animation, which using a normal luminance key, will be
unkeyable.
-JE
Heck, If you've got the video equipment, why not get a MAX, pull the frame into
the buffer, video post it with alpha, then lay it back out? Is this not
plausible? What makes this a in-elegant solution? ANY input will be filed away
in my cabinet. Thanks…
Chris Norman
A.M. Labs
Chris,
So far, real time grabbing with the MAX or the PAR is not up to the same
standards as what you are able to output. Its possible and so may do it but
you're going to lose a fair amount of quality in the process.
However what you could do is composite white into the Alpha channel and put
that to the MAX, and also output your animation to MAX, put the "matte" to tape
and key the MAX signal in realtime over the video using the flying matte for
the key. And you wouldn't need more than an A/B roll system.
-JE
Chris,
After re-reading your message and considering that you might want to do
titleing which can be generated with alpha, you could use the MAX to frame grab
your video and VP the titles over the top. However, the quality of the frame
grabbing is not as good as what you are able to output, and you will notice
degradation. Frame grabbing with a CRV or an Abbekas would produce much better
results.
-JE
In addition to Jim's reply, take a look at the description of Super Black on
page 7-109 of the Reference Manual. This lets you set a threshold limit for low
color values in the rendered scene so that nothing approaches true black
(0,0,0).
– Jack
Jack,
The problem with using Super Black is that very few keyer's are clean enough to
clip at Video Black. Ergo the need for creation of flying matte's.
-JE
I agree that Alpha-Split is the way to go, but since the original question was
about negative black, I thought I'd describe the option.
– J
Jack,
>> since the original question… <<
Of course that's appropriate. 🙂
John