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Why does my video have a lot of grain or video noise???

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David DiNenna
Why does my video have a lot of grain or video noise???
on Nov 11, 2009 at 5:58:29 pm

I recorded this with an HDV Sony HVRZ5U camcorder with a green screen, keyed the green out and embedded the video with in a SWF file. The raw video footage seems to be grainy but not out of focus. It gets worse when it's used in the SWF file. I know the SWF adds to the issue but does anyone have any good advice for capturing the video as clear as possible to start with - I'm a newbie so pardon if this is a basic question.

The video is on and the password is "insight". The video is just a welcome message so it only plays a few seconds. To see it again to view the issue just refresh your browswer and it the welcome video will run again.

thanks for any help anyone can provide!

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Dave LaRonde
Re: Why does my video have a lot of grain or video noise???
on Nov 11, 2009 at 6:28:11 pm

[David DiNenna] "I recorded this with an HDV Sony HVRZ5U camcorder with a green screen..."

No kidding. I see a TON of green light spill, and some really bad-looking edges. There are a number of reasons for your bad-looking key:
  • Green screen too close to the subject
  • Green screen lit too brightly
  • Green screen not lit uniformly
  • You're not sure what you're doing in Keylight
  • You're shooting HDV

Of the items above, the lighting and green screen proximity is more important. That animation is sufficiently small that you can scale the footage down to conceal HDV's many color resolution flaws. And on a vertically-oriented shot like that, you can also turn the camera on its side to take better advantage of that 16x9 camera's resolution.

You ALMOST NEVER get so lucky that you can pull a good-looking key with just one layer. And don't think you can run Keylight intuitively: you have to look at the Keylight documentation from The Foundry, and you should also check out the Keylight tutorials on the COW.

To salvage what you've got, try this:
  • DUPLICATE the green screen layer and use Keylight on the upper layer to pull a key with good edges on it. Use the Status view to get it right. Don't worry about graininess or the goofy colors that result. Change the keylight viewer to Final Result or whatever they call it, and turn the layer off.
  • On the lower layer, use Keylight just to remove spill, not to pull a key. You'll know it's right when the green background goes gray.
  • Use the good-key top layer as an Alpha Matte track matte for the spill-suppressed lower layer.

So what's the deal with HDV? It's about the worst choice you could make for chroma keying. The reason: lousy color resolution, perhaps even worse than DV's lousy color resolution. You owe it to yourself to watch the podcast in the following link, because it describes what bad color resolution like HDV's does to a chroma key:

Then there's also the fits HDV footage gives AE:

Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, mp4, m2t, H.261 or H.264 -- you need to convert it to a different codec.

These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.

In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

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