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Old June 29th, 2006, 07:47 PM   #1
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The Chroma Key King?

My son and I are planning on building a nice, large bluescreen area. (I've got a 36' x 36' pole barn on the property, and will pour a cement floor and put up drywall. The ultimate [pun?] plan is for 36' of screen on one wall and 12' on the adjoining wall, plus 12' x 36' of floor.)

Anyway, a good camera for bluesceen work is critical for us. I really like the HVX, but by the time you include camera, monitor and storage, it starts adding up. I was thinking of other options...

...like a 3-chip DV cam with component outs that we would capture uncompressed when doing foreground work. For backgrounds we would use DV. (Our targets are the web and DVD.)

But... None of the prosumer camcorders seem to have component outputs, let alone SDI. That would leave us with DV's 4:2:0 at 480p, which is really marginal for chroma keying.

Which brings me back to the HVX. Capturing 720p 24N in 4:2:2, keying and then downconverting will just plain kick DVs butt. I've seen some great results posted on this forum. It looks like its about time that I start saving my pennies for some P2 cards. Fortunately, I won't need to buy a capture card and RAID for live capture with this solution.

So, are there more cost effective solutions for (really good) chroma keys? Do any lower cost SD cameras have component or SDI outputs?

Or is the HVX simply the Chroma Key King of prosumer camcorders?
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Old June 29th, 2006, 08:05 PM   #2
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"Or is the HVX simply the Chroma Key King of prosumer camcorders?"

if not, looks like......;-)
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Old June 29th, 2006, 11:02 PM   #3
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DVCPRO HD (the codec the HVX shoots with) results in a far better key than anything you can get with DV or HDV. Far easier to get a good image.

BUT...the problem I am having is with Motion Blur...an effect you get with the 24PN and 24P frame rates. It looks very filmic, but keying it with the DVCPRO HD codec is...;proving difficult.

I tried DVGarage Pro ($199) but it didn't see thru the motion blur. It cut it down. And Keylight with After Effects, while it saw thru the key GREAT (and is really the best keying option around) produced additional artifacts. And the Chroma Keyer in FCP is very limiting.

But I bought Shake ($499...$250 for students) and will be using Keylight with that for it has more options to get rid of the artifacts. I'll post results on my blog at www.LFHD.net.

But I see you are short of funds. I will say that given the choice between DV and HDV...for Green Screen and Blue screen, I'd opt for the DV camera myself. Specifically the DVX-100a or b. HDV just has too many issues keying, IMHO...others might have had better luck.
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Old June 30th, 2006, 07:42 AM   #4
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Have you seen Jim Arthurs' greenscreen commercial project, or Anders Holck's greenscreen music video? Jim gives a great writeup on his experience using the HVX200 for an extensive chromakeying project.

http://www.dvinfo.net/conf/showthread.php?t=68442
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Old June 30th, 2006, 07:49 AM   #5
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Quote:
Originally Posted by Jon Fairhurst
My son and I are planning on building a nice, large bluescreen area.
Jon,

Do some recearch, but I think green is thought to be better for keying with video.

Others chime in.......

Mike
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Old June 30th, 2006, 07:52 AM   #6
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Quote:
Originally Posted by Shane Ross
HDV just has too many issues keying, IMHO...others might have had better luck.
I've had luck shooting HDV chromakey and then downsampling to SD DVCPRO-50 before keying takes place with Zmatte from DVgarage - you get 4:2:2 with this method.

I've also taken HDV into AE6, scaling down to an SD stage and using KeyLight. I got my best results with this method, but it's not really suitable for my most common requirement - talking heads in front of CG backgrounds.

Don't forget you can shoot DVCPRO-50 with the HDX-200 - that's very nearly digibeta. Certainly way off DV. P2 card friendly too. ;)

Quote:
Originally Posted by Mike Teutsch
I think green is thought to be better for keying with video. Others chime in.......
In a recent "This Week In Media" podcast, this was being discussed. Blue is usually the noisiest and weakest colour for digital cameras and green has a higher luminance so is easier to process. Green was more popular for corporate work (blue suits and ties <sigh>). Also talk of using blue and green together (e.g. to separate foreground and background keys).

On a tangential note, my favourite studio (which uses green btw) has loads of polyboard above the lighting gantry, and lighting the bgd is mainly a matter of bouncing 4 floor standing 2Ks off the poly... Simple but effective.
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Old June 30th, 2006, 08:46 AM   #7
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Quote:
Originally Posted by Matt Daviss
In a recent "This Week In Media" podcast, this was being discussed. Blue is usually the noisiest and weakest colour for digital cameras and green has a higher luminance so is easier to process. Green was more popular for corporate work (blue suits and ties <sigh>). Also talk of using blue and green together (e.g. to separate foreground and background keys).

On a tangential note, my favourite studio (which uses green btw) has loads of polyboard above the lighting gantry, and lighting the bgd is mainly a matter of bouncing 4 floor standing 2Ks off the poly... Simple but effective.
Yeah, at PixelCorps, we're shooting TWIM and MacBreak and such with one of those "ultimate" greenscreen cameras ... the CineAlta F950 capturing at 4:4:4

In the individually affordable range the HVX or the XL-H1 captured via SDI really seem to be the best options at the moment.

For green vs blue .... it's mostly dependant on your foreground. When you're not in 4:4:4, bright colors like white and yellow (blond) are usually easier to key in front of blue. These foreground colors have a high green value, so you get more detail out of the green channel. For everything else though, green is the way to go.
The recipe for a easy, great key is to start by shooting dark subjects (dark complection, hair and clothing) in front of a green screen. Many tools handle this with a click or two even with DV.

Probably best to make a green screen and just have some blue cloth available for special cases (bright stuff) where it would be better to use blue.

Have fun.
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Old June 30th, 2006, 12:05 PM   #8
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Regarding blue vs. green for chromakeying, none of our main actors have blue eyes, and they will typically be wearing green fatigues and camo. Sure, it's darker than green, but the hue would be very similar.

To be honest we're looking at more of a cyan. It's actually brighter than green (and less bright than yellow), and will have a unique hue compared to the foreground. There's no need to key on a primary color these days, assuming that the software gives the lattitude to choose the key color freely, as most do.

Regarding motion blur, that's something I hadn't considered. Fortunately, we will be under controlled lighting. We can plan to run the lights hot and run a fast shutter speed. Good monitoring and focus will also be critical.

But the real question was about less expensive ways to get a good chroma key. I'm terribly surprised that none of the DV cams have YUV outputs. Does anybody know of a lower priced camera than the HVX (HD or SD) that includes component outputs?
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Old June 30th, 2006, 12:34 PM   #9
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Quote:
Originally Posted by Jon Fairhurst
Sure, it's darker than green, but the hue would be very similar. To be honest we're looking at more of a cyan.
Yeah, green camo is still green and easier to key against blue.
Desert camo in front of blue would be easier for pulling good keys. :)

BTW: What software will you be using to pull the key?

Most of the better keyers today are based on Color Difference (RGB) or vector keying (based on a "3D" area where X, Y, Z are derived from Red, Green and Blue values in each pixel). Hue (traditionally a component of "Chromakeying" at TV stations) is not used as much these days in movie/TV post production.

As such, the best color for you will generally register in your camera with a high value in Blue and low values in the other two channels.
One way to select this color is to get paint sample cards from your paint supplier and shoot them in you studio with your lighting and white balance set.

This way you'll have a sampling of shades to review in the computer, letting you pick exactly the color that has the best separation for your key channel. Then just take that sample card back to the paint store and they should be able to mix up a batch of the "perfect" paint for your setup. :)
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Old June 30th, 2006, 03:35 PM   #10
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Thanks Nick,

I'm running Vegas 6 right now, which means that Boris Fx is my default. Looking at the controls, I'm going to want something better. (I helped design the Chroma Keyer on the Grass Valley Model 1200 switcher, so I have a good understanding of the processing involved, and the practical problems with chroma keying.)

I'm thinking that cyan is still a good choice. Rather than a blue only screen, we would have a "not red" screen. Both blue and green would be at full intensity with red at zero. I believe that the processing would work as well with a (1,1,0) [gbr] algorithm as a (0,1,0) algorithm. Heck, I could invert the video going into the keyer and invert the key to present the chroma keyer with (0,0,1) signal if I needed to. Please let me know if there's a flaw in my logic here.

Great tip about the color sample cards. We'll be able to get just what we need quickly and cheaply that way. It just doesn't make any sense to ship gallons of paint from B&H across the country.

One thing I hadn't considered before is that I'll want high color temperature lights for the bluescreen. Maybe that's a reason why so many have failed to get good key results in the past. Shining a red light on a blue object doesn't give much to work with!
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Old July 2nd, 2006, 07:29 PM   #11
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I was thinking other possible ways to get low-cost, high quality acquisition for chroma keys. For instance, what about an older analog Betacam? They certainly have YUV (if not RGB) outputs. But then reality hit...

They're interlaced.

60i only.

Bzzt. Next!

The HVX still looks like the King.
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Old July 2nd, 2006, 11:16 PM   #12
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Have you looked into the "ChromaFlex" solution? We purchased one and I'm very happy with the results, even with a DVX100A.

http://www.reflecmedia.com/content.a...chromaflex.htm
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Old July 3rd, 2006, 01:19 AM   #13
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Thanks Brian,

I had originally considered the ChromaFlex, but we want a bigger range of motion. Besides, drywall and paint are cheap. :)

The bigger concerns for me are the camera, the lights and the chroma key software - maybe in that order. I'm not ready to stand up for an HVX and P2 cards just yet, but the results I've seen look really great. I'd love to know if there's a way to get near that quality CK for less money...
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Old July 5th, 2006, 09:39 PM   #14
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These are all really great tips on pulling a better key. We shot an interview with the HVX in 720p24 and the results were less than expected. We thought we did everything right, greenscreen lit with a couple of 750's ten feet behind subject, subject lit softly with Chimera and ten feet from camera, zebras to check eveness of green (perfect), WB, and so on and so forth. We didn't have I regret a laptop to key on the spot. When we droppped into FCP (Chroma Key) the stairstepping was bad. We needed a lot of feathering to rid it, which is OK if the background is active, but we wanted a solid background so keying was not smooth. Can't wait to try again with the tip about hairlighting with orange/mauve?
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Old July 6th, 2006, 10:59 PM   #15
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I had a unique opportunity to visit Peter Jackson at Wingnut Films, to give him and some of his staff a one-on-one training seminar on how to use their HVX200's and HVX202's. PJ has bought some for use on his own projects, and his companies WETA Digital and WETA Workshops also bought them for professional use.

While I'm not permitted to tell you exactly what they are used for, I can tell you that some of the WETA Digital guys did some comparison chroma key tests between the HVX and XDCAM-HD, and found the HVX to deliver a substantially better chroma key. They were very happy with the chroma key results they got from the HVX.
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