for dvx100a use greenscreen? or black screen?

B

Bruce Morgan

Well-known member
Hello All
I am still in the dvx100a world .
So having read all the pro and con on the green screen prep for the dvx100a (a real compromise in some cases ) ,I have a few questions .
QUESTION#1
With the advance in software would there be any way to just go with nutral grey to black background and just rotoscope the moving images out?

Issue
I am under the impression that once you start processing your green screen element you face blocky pixel units and other abberations .I also have a hunch this may affect the forground image in final rendering .CORRECT or Incorrect?
There are some new software composite applications like Shake that may key off grey or black so :
Question #2
Do I just join the crowd and GREENSCREEN MY SHOTS ?
OR
QUESTION #3

IS THERE A NEW WAY TO GREY OR BLACKSCREEN THE SHOTS TO AVOID THE DISTURBING BIG BLOCK SQUARE PIXEL ISSUES WITH DVX100A AND GREEN SCREEN ?.
THANKS TO ANY AND ALL FOR ADVICE .
CHEERS
BRUCE
P S LAST TIME I BOUGHT BLUESCREEN FABRIC IN LOS ANGELES (FOR A FILM ) THERE WAS A NICE STORE CALLED DAZIONS WHERE THEY HAD A FABRIC CALLED TEMPO BLUE

SO
ANY ADVICE FOR BUYING LOCAL IN LA ????
THAT WOULD BE A GREAT HELP AND
HELLO
RUSH

YOU OUT THERE LISTENING TO THIS CRY FOR HELP?
I COULD USE YOUR ADVICE ABOUT NOW
WE ARE SHOTING IN SEPTEMBER
THANKS AGAIN
BRUCE
 
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There are a number of people in the forums who seem to be quite happy with the results they are getting in DV chromakey. I tried everything I could think of or could find and never got results that were tolerable for my application. I have a sense that DV chromakey is really more of an assist for rotoscoping, and that to get good results you end up painting the individual frames in photoshop.

DV chroma IS going to produce 4-pixel squares of color at the edges. It doesn't really matter what color you are using, as all the color is compressed in this way, so even keying in red or black is still going to produce 4-pixel artifacts at the edges.

My best results came from getting an even fringe of artifacts around the edge of the object, and then throwing a choker onto it in After Effects. The choker will interpolate back to the edge and it looks okay in any static image. Of course, if there is movement in the scene, then the edge of the choker is going to change, and there will be artifacts popping into and out of existence at the edges. I think this would work with a stationary object -- like a newscaster shot -- where all the motion is in the face and the edge isn't moving.

The luminance is at full resolution. I've tried a couple of approaches to leveraging the luminance. Supposedly, some people have had luck with Shake in combining the luminance information with the color to be able to differentiate the edge. It has something to do with converting the image to CMYK and working with channels. I don't have Shake so I couldn't follow the example. And I tried to simulate it in After Effects but the results were disappointing.

I tried Ultra, which is a vector program that interpolates the edge. It produced about the same results that I got with the choker trick -- artifacts popping in and out at the edges as the actor moved. It was much faster than tinkering in AE, but I didn't get better results.

I had read about using black for compositing. If you use AE's luminance blend mode it will treat black as transparent and gray as some degree of transparency. Its supposedly good for compositing translucent effects like white smoke shot against a black background. I tried it with actors, trying to get them well lit, but they end up being slightly transparent in the composite -- useless.

Depending on budget, time, and amount of chromakey you are using, you might want to look at renting an HVX and shooting in 4:2:2 in either DVCPRO50 for 4:3, or if you are shooting in 16:9, then you could shoot in DVCPROHD 720 or 1080, perform the chroma in high-res, and then reduce the resolution to DV. That will give much better results than shooting with the DVX. But its all a trade-off of time, money, and quality that you want in the final.

You won't get perfect chromakey without 4:4:4. But 4:2:2 on the HVX can produce some great results.

Last advice -- test before you commit. You need to be able to produce the results and to be satisfied with them. I found that I couldn't duplicate the results others got in DV no matter how hard I tried. So its not just a technology, but your facility with the techniques behind it.

Good luck!
 
ANDY! Thanks so much
This is more detail and case history than I expected and it does help .
I will test .
I do have shake and it looks like i sm headed for black or grey screen or no screen and in post for photo shop with magnetic laso rotoscope frame by frame ,,,
"Arrggg!"
(said the film pirate as he toyed with video.)
any shake experts out there ?
Cheers and Thanks
Bruce
 
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use ultra 2 it fixed all those problems i had the same problems and it 2 fixed it well. Also try pumping alot of light into your footage. Black is not good for humans mainly because we naturaly have pigments that messit up. Green and blue are good. For explosions and such for stock footage black works awesome. Ultra 2 is amazing and dvrack go realy well hand in hand. I hope this helps.
 
We've been having better success keying subjects against a white background and doing a luma key witha garbage matte for anything on the person. It definately takes care of the green edge blur.
 
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