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Old September 25th, 2003, 09:46 AM   #46
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UltraKey which is a new product I use from Serious Magic also creates excellent keys in the worst conditions and lighting. It also includes a lot of virtual sets. (seriousmagic.com)
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Old September 26th, 2003, 09:50 AM   #47
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Thanks Jim. I keep seeing their adds in all the video magazines and it makes me wonder if it really works that well. I also read the DV article on chroma a while back and have employed their techniques.

I think my main problem has been that my subject is too close to the screen and the green spill is getting on them. I took the advice of my local Kino salesman and bought green tubes to light the background and that makes the green bounce really far back off the screen. Using white lights improved the matte on close range and I'm going to rearrange my screen today so I can get my subject over 10' from it... then I'll report back.

I already have a Canopus RaptorRT (about 1 year old) which is supposed to be exceptional at green screen... so I'll continue to experiment before I give up on it and try seriousmagic.

Bill, are you "BillKC"?

Anybody else notice that somebody else started the exact same thread a couple days after mine? I'll take the combination of answers from both and hopefully he will too.
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Old October 2nd, 2003, 08:57 PM   #48
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Anyone have any new blue/green screen experiences?

I've asked this befor but I am anxious to hear of anyones experience.
Any problems with chroma noise? Any colour backing you find works better or worse than another?
Any particular lighting or filters that help?
Thanx Ken
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Old October 2nd, 2003, 11:30 PM   #49
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DV25 isn't the best format for green screening but with a little work you can get some decent results.

1. make sure your green screen is eveningly illuminated.
2. keep your subject a good distance from the screen

Most prosumer NLE's have chromakeying capabilities so that shouldn't be an issue. Also, do some searches, there are a lot more tips out there then I gave you.
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Old October 3rd, 2003, 12:41 AM   #50
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Ken is asking about the chroma keying in regards to these JVC HD cams, I understand.

Of course, general green screen suggestions apply as always.

In short, my experience with HD10's green/blue screen is exactly what I expected: it sucks.

JVC HD cams' chroma noise is crazy on all same-color surfaces, which by definition includes green/blue screen areas.

Quality 3 CCD miniDV camcorder produces *much* better results with keying because of the lower chroma noise.

If someone has a different experience with JVC HD cams and keying, then tell us how do you fight the chroma noise and I'll be happy to stand corrected.
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Old October 3rd, 2003, 09:27 AM   #51
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DV can be as good as betaSP for chroma keying if using the right tools. Some NLEs aren't that good at chroma keying (premiere 6.x for example).

From Adam Wilt's DV FAQ:

Can I chroma-key with 4:1:1 / 4:2:0?
Yes indeed. Many early DVEs were 4:1:1 internally; plenty of digital boxes out there still are (such as the Panasonic WJ-MX50 and Sony FXE-series vision mixers, both of which chroma-key). As previously mentioned, BetaSP could be considered a 3:1:1 format in terms of component bandwidth, and BetaSP is used for chroma-key applications all the time. With some care, DV25 keys at least as well as BetaSP; read on...
Part of the standard JVC sales pitch for D-9 is the superiority of 4:2:2 (which is true), and the utter doom and degradation that awaits you should you try to do anything -- including chroma-key -- with a 4:1:1 format (which is, shall we say, a wee bit exaggerated). But that doesn't mean that you can't do very satisfactory work in 4:1:1.

JVC has an excellent D-9 demo tape showing multigeneration performance comparisons of DV, D-9, and Digital Betacam; watch it if you can. Just be sure you take the hype with a grain of salt.

True, the chroma performance of 4:2:2 formats is superior to 4:1:1 formats, especially in multigeneration analog dubbing. But by the same token, 4:4:4 is as superior to 4:2:2 as 4:2:2 is to 4:1:1 or 4:2:0.

Where DV can get into trouble is that the coarse resolution of the chroma signal (only 180 samples per scanline in 4:1:1) leads to a very regular, "steppy" key signal, most noticeable on near-vertical edges or vertical edges where motion is present, especially if the codec's decompression simply replicates the chroma sample across the intervening pixels instead of low-pass filtering or interpolating between samples. The 4:2:0 sampling in 625 DV/DVCAM is somewhat better in this regard, but it has its own problems vertically, so there's always a tradeoff.


The single most important factor in good DV chroma-keying is low-pass filtering or interpolating the chroma prior to applying the keyer, so that the “steppy edges” are knocked off. Some codecs do a pretty good job of this by default (Avid DV); some can be set up for it (Matrox: Control Panel > Sounds and Multimedia > Hardware > Video Codecs > Properties > Matrox VFW Software Codecs > Settings... > Chroma Interpolation (YUV -> RGB)); with others you can add a filter (I have filters for FCP here). Some people capture DV for chroma keying using an analog Y/C feed, since the analog connection prefilters and smooths the chroma. The Matrox RTX.100 DV NLE board uses multi-tap resampling of DV's chroma to generate astoundingly good, crisp, finely-detailed keys in real time – so there is certainly enough information on DV's chroma for most keying purposes; the only tricky bit is recovering it intelligently!


Additionally, use the matte choker and/or matte feathering and smoothing controls of your keyer to round off the edges a hard-cut key signal gives you. I've had excellent results with After Effects Production Bundle's Color Difference key, and superb results also using the Chroma Keyer in Final Cut Pro 3. Using these tools I can make very clean and acceptable keys, certainly for hard-edged keying. Spill supressors (or “edge enhance” in FCP 3's Chroma Keyer) are essential in cleaning up any remaining chroma spill in the foreground video.

You may also find that layering different key signals gives you excellent results. I've used a heavily-choked chroma key to cut my main matte, but then add one or two luma, extract, or difference keys to define the edge detail that the chroma key can't get. Each luma key may only work for a small part of the image; it may lose the greenscreen background but also lose the interior of a similarly-bright face. However, it usually is able to get edge detail, because the edges of a person fall off in shadow or are picked out brightly by the rimlight, and the chroma key holds the interior matte that the luma key won't provide.

John Jackman has some good examples on his post-production pages at greatdv.com.
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Old December 23rd, 2003, 01:15 PM   #52
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green screen

Hello,

i recently shot some green screen footage with the DVX100. Considering my limited knowledge in lighting, it turned out ok.
Though my only concern in how to eliminate the green bleed that appeared around the edges of the subject, i could also use some advice for the backdrop lighting of the screen itself.

any thoughts would be appreciated.

Thanks
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Old December 23rd, 2003, 01:47 PM   #53
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Depends a lot on which software you are using. Normally you
feather the edge of the mask (ie, you blur the edge) so that the
foreground will blend into the background. Some blue/green
screen software has specific functions to remove spill.

Most people advice to have the actors / objects futher away
from the screen to remove spill. But if you have already shot
the footage this is not possible, ofcourse.
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Old December 23rd, 2003, 02:12 PM   #54
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Which NLE or keying program are you using? Some of them don't apply chroma interpolation/smoothing unless you get certain filters or tell it to. That will improve your results.

Also note that the DVX has a pulsing chroma problem on pans. Check out Adam Wilt's website for info on that.
http://www.adamwilt.com/24p/index.html
The DV FAQ on his site gives great information on other things like getting keys from DV (talks about the chroma interpolation thing I mentioned).
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Old December 23rd, 2003, 02:17 PM   #55
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these were stationary shots. I am using After Effects chroma key.
I tried even using Combustion, not much better. The down fall of the bleeds is that the edges tend to get a bit "crawly" softening them jsut makes it smudgy after keying out the green....I noticed the backdrop wasnt as smooth lighted as it could of been..

anyone have any tips on the backdrop lighting??
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Old December 23rd, 2003, 03:51 PM   #56
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If you are in AE, you want to use Spill Supression.

If you want a really good article on keying in AE, check out my website. I have a tutorial on how to create the StarWars Hologram effect.

Cheers
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Old December 24th, 2003, 12:00 AM   #57
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Adam,

Your background should be evenly lit, no hot-spots or drop-offs, and slightly "hotter" than your foreground subject. Separation, distance wise, from the BG is also important in that it will help reduce any contamination from the green caused by reflection.

Another way of combating the contamination problem is to use a soft rim or backlight light with an amber or straw gel.
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Old December 24th, 2003, 12:00 AM   #58
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Adam,

Your background should be evenly lit, no hot-spots or drop-offs, and slightly "hotter" than your foreground subject. Separation, distance wise, from the BG is also important in that it will help reduce any contamination from the green caused by reflection.

Another way of combating the contamination problem is to use a soft rim or backlight light with an amber or straw gel.

RB.
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Old December 24th, 2003, 11:57 AM   #59
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Since you've already shot the footage, it sounds like your best bet will be to use a garbage matte over smaller portions of the image, that way you get better control of the key. I do lots of "home" greenscreen, and I have yet to get an evenly lit background. I always have to break the image into smaller pieces to get a good key, usually anywhere from 9-16 layers! Takes a while, but you can get decent results that way. for an example, check this out:

www.jeffersons.org/bball.wmv

In some cases, I have 16 layers. The greenscreen looked as evenly lit as I could get it, but the interview outtakes at the end show just how un-evenly lit the image was. Keep in mind that the lighting looked completely flat when I shot the interviews.

Cheers,
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Old December 26th, 2003, 05:49 PM   #60
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Mark,

on the field monitor, the screen looked evenly lit as well, untill ofcourse i brought the footage into AE. I ended up using color range, spill suppressor, and some additional layered masks. the footage came out decent. Thanks for the help guys, ill post a link when im finished.

-Adam
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