Green scrn keyed w/ blue back ground =Jaggies ??

will-3 wrote on 7/14/2008, 3:55 PM

The question: Is it impossible to get good key's in Vegas when the new background is a dark color... like solid blue?

Here's what happened...
- We are shooting chroma key on a green screen backdrop.
- We chroma key it using Keith Kolbo's method... the key looks good.
- We use a Media Generated solid blue background...
- Red = 0 Blue=255 Green = 0

We render and the render has jagged edges?
We change the Blue background to other dard colors... same results.
We change the background to a light color and the key looks great.

- We were using a photo background with a light blue sky and never saw this... renders looked good.
- We changed to a dark blue Digital Juice motion background and discovered the problem
- We reduced the process to the simplest setup...
.. original green screen clip
.. blue media generated background
- rendered... and the results do not look good.

Thanks for any help. We really need to get this fixed.

Comments

John_Cline wrote on 7/14/2008, 4:14 PM

I assume that you're rendering to DV and, if so, you have run into the limitation of the 4:1:1 colorspace. This manifests itself as vertical "stripes" about 8 pixels wide and they are most noticable on highly saturated solid colors, particularly on diagonals. The effect can be minimized by not using a solid color, or turning the saturation down, or adding a tiny bit of noise to the background.

fldave wrote on 7/14/2008, 6:08 PM

Don't use a pure color background, maybe try 24,230,24

If there is a lot of motion in the subject, set your Project properties to Interpolate instead of Blend.

Use Best quality in your render.

What are you rendering to? If you are rendering to MPEG2, then make sure you go into the properties of your template and set the quality slider all the way to the right, value 31.

GlennChan wrote on 7/14/2008, 8:40 PM

If you are outputting to a format better than DV, then don't render to DV in between.

What's your target output format?

will-3 wrote on 7/15/2008, 5:15 AM

Thanks for the comments everybody.

Our final render is to mini-dv tape for broadcast on local cable. They broadcast the tape directly on their system and do not dub or copy it to another format or whatever.

In answer to the questions... here is the process...
1 - We shoot the talent on a green screen and capture with Vegas 5 directly to hard disk as an AVI file...
2 - Take that AVI file and put media generated white text on it
.. plus a very blue motion lower third with white media generated text on top of it
.. on the bottom track is our very blue motion background
3 - all that is chroma key'd & rendered to an AVI file(s)
4 - We have a collection of these AVI clips (multiple talent) and place them all on the final program time line with other clips.
5 - We apply the Sony Broadcast Colors filter to this final video track with the consertative settings.
6 - We then render all these clips with music background to one final 30 minute (6GB+) AVI file.
7 - We then print that file to mini-dv tape and deliver it to the cable studio's for broadcast.

Any suggestions on this process would be very helpful.

Thanks everybody!

fldave wrote on 7/15/2008, 6:03 AM

Don't use pure white text
Don't use pure blue

Text media size should be 2x the size of your final output (1440x960 for DV)

Use Best

If you use pure colors, specially outside of the Broadcast range, then you are going to run into trouble.

GlennChan wrote on 7/15/2008, 2:34 PM

.. plus a very blue motion lower third with white media generated text on top of it
The easiest thing to do is to knock the saturation on the composited elements down. DV just won't handle pure saturated colors well. Apply the color corrector FX and knock the saturation down.

dirtynbl wrote on 7/15/2008, 2:48 PM

Also, Chroma Blur. Make sure use use that a little bit. It doesn't always help but is pretty useful for smoothing out keys.