You going to have troubles a-plenty, sir, and that's no joke. Whoever shot that video had no stinkin' concept of how to shoot for chroma key. No clue whatsoever. It's high-school quality. You can tell the shooter I said so, and you can quote me.
• The first essential for a good key is a flat, uniformly-lit background. But look at the light falling on this key background: it's hot on the left, and dark on the right. Apparently the concept of using a light meter or a waveform monitor to get even lighting is lost on your shooter.
• The second essential is to separate the subject from the background to minimize background spill on the subject. But look at the spill on the edges of the podium: it's not even brown, it green, for cripes' sake!
• The third essential it to light the subject and the background SEPARATELY. That way you can adjust the lighting on them separately to get a good key. But look at the right edge of that picture: the guy's stinkin' shadow is falling on the green screen! You got some great separation goin' there, you bet!
• The fourth essential is to avoid DV like the plague. Okay, it's actually DVCPro 25, but it's just as bad. DV and DVCPro 25 use the same kind of color resolution, 4-1-1. So I'll just refer to DVCPro 25 as DV.
The reason is color resolution, also known as color sampling. The color resolution of DV video is about as bad as it gets. Oh, it's good enough to fool the human eye, but computers are a LOT more discriminating, and DV's stinky color resolution poses real challenges for chroma keying.
I recommend watching a podcast by Alex Lindsay, the founder of DV Garage and Pixel Corps, called "The Road to 1080p Part 2". In it you will find an excellent description of the differences between 4-4-4, 4-2-2 and 4-1-1 color resolution, and you will come to understand the challenges of keying DV. It's WELL worth the 15 minutes it takes to watch.
You can get the podcast here:
http://macbreak.libsyn.com/index.php?post_id=70596
As you watch if, keep in mind that Alex Lindsay runs a company that makes DV chroma keying plugins... and he STILL doesn't recommend trying to chroma key DV.
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So how do you save this footage? You don't. You try to minimize the warts in it. You split your keying efforts up into multiple regions. Split the footage at about the subject's right shoulder and do two separate keys: one for the too-bright key background, and one for the too-dark key background. You may have to split it into even MORE sections.
On the COW, look at Aharon Rabinowitz' podcast on creating super-tight junk mattes. Andrew Kramer's also got one on using Keylight. You NEED to know how to use keylight -- you can't use it intiutively, or you'll hose yourself.
Or you do the wisest thing possible: re-light and re-shoot.Dave LaRonde
Sr. Promotion Producer
KCRG-TV
