Chroma Keyer - how to achieve good results?

ingvarai wrote on 12/15/2008, 2:16 AM

In the professional world:
I watched the background documentaries on LOTR. Here they carelessly throw green blankets everywhere where they want the background to be replaced, and in the final movie the green blankets are replaced by another picture, no antialiasing problems, no visible borders - it just looks great.

In my world:
I put a green blanket on the wall, and stand in front of it myself, speaking. I want to replace the background with my own stock shots, from a street the last summer, in a city, in another country - far away.
Problem is, while I can make the chroma key trigger on a relatively flat portion of the blanket, evenly lit, any other portion of the blanket that has a fold, has a little shadow, will not work.
Oh yeah, I can tune the chroma key, but then other "interesting" things start to happen, the edges around my face get dissolved, parts of my clothing (I wear no green clothes!) start to disappear as well.

Question is: Is this a game for professionals only, using mega expensive gear, or can it be achieved by amateurs like me, too?
Should I use a "green blanket" especially designed for this purpose?
And does more efficient software exist, that does the job better than the Vegas built in Chroma Keyer?

Comments

farss wrote on 12/15/2008, 3:23 AM

For starters what you don't see is how much work goes into getting those keys tweaked in post. I don't just mean adjusting the keyer I mean manually fixing what it can achieve e.g. rotoscoping. Also keep in mind that a lot of the keying done for movies is for set extension. When it doesn't move you don't need a key, just a mask.

Secondly, for certain the chroma keyer in Vegas is just a basic keyer, more money buys you better tools. Keylight that comes free with AE is pretty good but there seem to be better. Also with better tools you can use a keyer to create a bezier mask, then you can tweak that.

Thirdly LOTR was shot on film. Scanned film has more resolution, more chroma samples and a bigger color gamut. I don't have the experience to say for certain how much each one of these helps but the combination has got to make for a big difference.

Lastly and from my experience most importantly. Having the good tools is one thing, acquiring the skills to use them to their full potential is quite another. No doubt the people doing visual fxs for the big budget movies have been using the same tools for a long time, they know which one of the zillion sliders to tweak and how they all interact. I have Keylight and it is very capable, much more capable than I am. I think that's where the big budget productions have a big head start on the rest of us. They can afford to employ people with specialised skills.

Bob.

ingvarai wrote on 12/15/2008, 4:11 AM

Thanks Bob,
it just struck me, I believe the "green blanket" color should be as saturated as possible, right? I start to belive that my blanket is too light. Or is this unimportant?
BTW, I noticed somehting that puzzled me, when using "pure green" I get a better result than using the eyedropper directly on the blanket. Hm..?

they know which one of the zillion sliders to tweak and how they all interact.
Understood. But my blanket hanging from the ceiling, just behind me, ought to be one of the less challenging tasks for a chroma keyer.

Found this thread afterwards:
http://forums.creativecow.net/thread/24/882483

farss wrote on 12/15/2008, 4:26 AM

Yes,
ideally the blanket should be pure green. You should sample the key color close to the subject. If holes appear away from the subject a simple mask will get rid of them.
Ideally you need at least two lights to light a screen. Big sources are good for getting even light. Wrinkles are bad. Daylight lights are better than tungsten. Screen should be 1 stop darker than subject.

If things get messy you can use more than 1 CK FX.

Hope that helps. There's heaps of good tutorials on the web that cover this in great detial. I agree that should be a simple thing to key.

Bob.

biggles wrote on 12/15/2008, 5:10 AM

Here is one tutorial I found really useful:

http://www.vasst.com/index.php?option=com_content&view=article&id=515:great-chromakeys-in-sony-vegas-movie-studio-and-sony-vegas&catid=41:all-tutorials&Itemid=73

Wayne

TheHappyFriar wrote on 12/15/2008, 5:48 AM

depending on what you've got, conegobs keyer works very well. I combine the use of that + vegas keyer to get decent results.

DV/HDV just isn't great to get a screen out of. Odds are you'd be better doing a difference mate vs the chroma key if you're not moving the camera.

To get that take a few second of footage w/o the object infront of the screen/area. Then, w/o turning the camera off, put what you want in front of the screen/area. Now you have a few seconds of stuff you want to get rid of. I forget the exact proedure, double check the help file for "difference mate".

(did I spell mate right?)

farss wrote on 12/15/2008, 11:52 AM

"(did I spell mate right?)"'

It's "matte", mate :)

Bob.

cbrillow wrote on 12/15/2008, 4:29 PM

"(did I spell mate right?)"

Nope, and you also butchered "cinegobs", but who's counting? (grin)

You provided some useful information -- that's what counts. (and the link was ok...)

ingvarai wrote on 12/15/2008, 4:53 PM

Bob,
Secondly, for certain the chroma keyer in Vegas is just a basic keyer, more money buys you better tools.
I have experimented with the built in Chroma Keyer in Vegas, and have found out that it is way better than what I thought. On of my mistakes was to use the eyedropper and not fine tune the RGB values afterwards.

What I do now:

- Add a Chroma Blur FX, set it to maximum values (4000)
- Add a Chroma Key FX
- Select "show mask only"
- Use the eyedropper and select a suitable portion of of the green carpet.
- Move the RGB controls back and forth, until as much is achieved as possible (carpet as black as possible , foreground as white as possible
- First now I start to adjust the HIgh and Low treshhold sliders.

Then I follow this tutorial:
http://www.vasst.com/index.php?option=com_content&view=article&id=515:great-chromakeys-in-sony-vegas-movie-studio-and-sony-vegas&catid=41:all-tutorials&Itemid=73
Thanks to Wayne for this link

I must say, I am impressed by what can be achieved with the built in FX in Vegas. Having a green screen only lit by the ceiling fan light, and putting myself in front of it, I was able to completely remove the green carpet, with only a very little "green spill" on my shoulders.

Dach wrote on 12/15/2008, 6:20 PM

Since I just finished a project that involved keying I thought I would chime in.

Our project was strictly done within Vegas and I am very pleased with the results so far. We invested in a material offered by EEFX and compared to having used chroma key green paper on past projects that was a good investment.

We used a key and fill light and added a hair light, which I also believe was a much needed requirement. In Vegas both the Chroma Key feature as well as Secondary Color Corrector was used.

If we had to do it over again, I would have desired being able to put the talent another 5 feet in front of the actual screen. In our case it was only about 6 feet.

Chad

farss wrote on 12/15/2008, 6:50 PM

I wasn't belittling the CK that comes with Vegas. Remember your original question was how come the Hollywood guys can pull perfect keys from shots where so little care is taken. Not only are they perfect keys they still look perfect on a the big screen where every pixel is pretty big.

As I said originally having much better source material makes a big difference, that applies as much to the CK FX in Vegas as their expensive tools.

You can get better results out of the Vegas keyer by adding chroma blur before the keyer. That'll probably not save things like fly away blonde hair but it'll get rid of a lot of the jaggies. Also be careful to test your outcome by putting a solid color background underneath your key. The slightest transparency in the subject will let the keyed over background show through and give subtle to wierd results.

What you get with the more expensive keyers is things like spill suppression/correction and mask choking and smoothing. The best one seems to be Ultimatte, way out of my price range and I simply wouldn't have the time to learn how to use it to it's full potential. Even with Keylight I've carefully studied the online tutorials and tried getting the same results from the exact same media, it is not easy. I take my hat off to those who can.

Bob.

Steve Mann wrote on 12/15/2008, 10:58 PM

"... depending on what you've got, conegobs keyer works very well. I combine the use of that + vegas keyer to get decent results."

Which do you use first? Cinegob or Vegas?

ingvarai wrote on 12/15/2008, 11:41 PM

Bob,
be careful to test your outcome by putting a solid color background underneath your key

Very good advice, an invaluable advice!
Now I am almost where I want to be, using Vegas FX only. I discovered the Secondary Color Correction FX!!
Armed with this weapon (I insert it before the Chroma Keyer), it seems I can get magic results.

This thread has taught me to use Vegas in a new way, chroma keys or not.

Massimo Rossi wrote on 12/16/2008, 6:24 AM

I've tested and used several keyers and none of them seems to be better than Keylight, by The Foundry. It does really an EXCELLENT job, even on bad footage. It really makes the difference for me, being capable of key out footage simply impossible to work on with others keyers.
It saves a LOT of work, time and frustation... I know the Vegas keyer very well, but I'm not able to get the same results with it, if compared to Keylight. I really hope in the future it will come included in Vegas, as it does with After Effects.

Bye.

TheHappyFriar wrote on 12/16/2008, 8:22 AM

Which do you use first? Cinegob or Vegas?

I normally test both @ the same time. If one gets me much better results, I use that one & then do a 2nd pass with both again if need be.

BTW, I think I found the perfect small-object matte (got it right!): your LCD monitor/TV. Put a solid color on the screen, put an object in front of the screen, light the object, and you get a near-perfect key for the camera.

Steve Mann wrote on 12/16/2008, 9:49 PM

LCD TV - it makes sense because it is an evenly 'lit' background, which is *the* key in keying.