Can anyone explain to me in simple terms what the heck is going on here? Recently I set up a green screen in my room. I painted a piece of smooth plywood with a recommended (green screen color) ....and lit the green screen equally. In other words. An equal amount of light was hitting all parts of the screen. So I got in the front of the green screen and moved around a little, while capturing the footage with my xl-2 ...i used the chroma option in VEGAS ...and it never really looked that great. When I would try to key out the green, you could see where the light was uneven because it would key some parts of the board before it would key other parts.

So then i start looking at behind the scenes footage of Sin City and Matrix, and you see these huge green screen set ups, but there are dark areas all over the place. I mean you can clearly see very dary shaded areas on the green screen. How do they get away with that? Which brings me to the panasonic hvx200. My friend was telling me that it has to do with 4:1:1 ..4:2:2: and all that. Is that true? ....Will the HVX200 be better for green screen vs. the xl2??

thanks ..

j.


PS. if the HVX is better for green screen than the xl-2, anyone wanna buy an xl2? :)

Well for one they are using sweet stuff like Ultimatte which will key just about anything well.

Yes the HVX should be much better for keying. Twice as much color information!

Wow, Ultimatte? I looked at their website but theres a bunch of stuff. If i was shooting footage of spaceships in front of the green screen, then wanted to throw in a background in post, would i just need the Advantedge software from ultimatte?

thanks

j.

Ultimatte is good, but Primatte is more user friendly. If you have After Effects, you can also use Keylight, which is excellent.

The fact of the matter is, pulling a matte from a greenscreen or bluescreen setup isn't a simple process, it's still a bit of an artform. There are plenty of good keyers out there like ultimatte, primatte, et al., but they will only take you so far. In other words, they are great at getting you most of the way. But what makes a truly good matte is in the details.

Unless you've got a perfectly shot element already, getting a good matte requires a fair amount of tweaking, and in many cases, requires multiple keyers setup for different parts of the image! (This is especially true when shooting people)

Keying something like DV footage, which has very little color depth, low spatial resolution, and a fair amount of compression artifacts only multiplies your headaches. So, as Aaron mentions, the HVX presumably will be better for keying, assuming you shoot your greenscreen footagre in HD as opposed to SD, but it's still nowhere near "ideal".

<<<-- Originally posted by Casey Visco : . . . So, as Aaron mentions, the HVX presumably will be better for keying, assuming you shoot your greenscreen footagre in HD as opposed to SD, but it's still nowhere near "ideal". -->>>

Although the extra resolution of HD will help, it is compressed more, too. The HVX will offer DVCPro 50, which also has 4:2:2 color sampling. This should help with keying in SD.

Someone correct me if i'm wrong, but..

Concevably, it would work well to shoot HD (on the HVX) and do your keying in HD. Then use that keyed footage in a SD project.

- Mikko.

Here's a question:

Okay, I know as much about how colorspace works as I do brewing beer... no wait, I know how to brew beer... I know as much about how colorspace works as I do about competing in the olympics... so this may be a pretty obvious answer to some...

Anyways, I remember people saying that you could capture the HDV footage at 4:2:0 and downconvert to end up with 4:2:2... Is there any advantage to capture this DVCPRO HD footage at 4:2:2 and downconverting, or does it pretty much stay at 4:2:2?

It would stay at 4:2:2. With HDV to achieve SD 4:2:2 you would have to discard one field which would leave you with interlacing issues I would imagine.

"I remember people saying that you could capture the HDV footage at 4:2:0 and downconvert to end up with 4:2:2"

if the theolor space to TAPE/computer was 4:2:0 it will NEVER be able to get to 4:2:2 = you can't get what you never had in the 1st place .. you could also downconvert to 4:4:4 but again the material will never be 4:4:4 it will always have the 4:2:0 color space for green screening ...

Aah.. i wasn't talking about downresssing to improve color space (impossible).

I was talkign abotu dooin ghte best keyign you can in the HD colorspace, then downrezzing to hide any erros. (the same way you can get away with slightly soft focus if you are shooting for the web...)

- Mikko.

John: check out these green screening tutorials for Vegas, they explain how
to work with color differences etc., in my opinion Vegas has a pretty decent
keyer actually!

http://www.digitalpostproduction.com/articles/viewarticle.jsp?id=31596
http://www.digitalpostproduction.com/articles/viewarticle.jsp?id=31478

I must have missed it but.....does Ultimatte advantage allow preview with a background overlay while shooting? I need an answer ASAP. Got a shoot coming up and I use a Mac. If U.A. doesn't allow preview, I'll have to get a PC and another software which does. That will put a cramp in the budget!

There's a difference between having a preview overlay while shooting and pulling a good quality key. Even the big boys use inferior technology to pull "live" keys. The ultimate setup would be to have an Ultimatte hardware unit on set. The results can look mighty impressive, but it's always best to have the original bluescreen or greenscreen footage, then do a key you can tweak in post, resorting to multiple keys or rotoscoping when you need to.

The point is, a live key is only used to check composition, contrast and color balance. It doesn't matter if the edges of the key are perfect, just good enough to give you an idea of how the final composite will come together.

Maybe a cheap, used switcher with a chromakey function might be a good tool for on-set previews, then use high quality software like AfterEffects or the Primatte plugin for your keying in post. You could even rent a low-cost switcher for the day of the shoot - probably for less than $50.

Definitely worth you checking out ULTRA too, which uses a vector keying system that doesn't require a perfect screen. Its not too expensive, it has a great set of videos you can check out on their site and there's also a trial you can download. Impresses me anyway!

Thanks for the link to the Digital Post Production site, big big fan of Vegas so always glad to find sites that offer information and tutorials with it.

Down-converting 1080p DVCPRO-HD to SD will yield 4:4:4 SD and excellent keying. (essentially 100 Mbps 4:4:4 SD - uncompressed SD is 238 Mbps).

DVCPRO-50 will offer 4:2:2 SD at 50 Mbps, and will be inferior to 1080p DVCPRO-HD for SD keying.

At HD resolutions, on a per-pixel basis, DVCPRO-HD is just as compressed as miniDV, but offers increased colour information (4:2:2 over 4:1:1) and introduces more spatial compression. I would expect that at native 1080p resolution DVCPRO-HD will key about as well as miniDV, however, I do not have an appreciation for how large an effect mosquito noise has on a good key, in comparison with colour space. Does anyone know which is more important for good keys?

-Steve

In order to try and get down converted HD close to a 4:4:4 SD the resolution would have to be half. The sad thing about DVCpro HD 1080 is that it is only 1280 pixels wide. This means in order to get a good 4:4:4 down convert you will end up with 640x540. This would then need to be scaled up and interpolated either to 720x480, 853x480, or 960x540.

Even though 4:2:0 HDV can offer problems in trying to get a good 4:4:4 at least it is 1440x1080. This means we can get a natural 720x540 image in 4:4:4 which can then be scaled down to a anamorphic 720x480 for DV or DVD. Of course these numbers only work great for NTSC. PAL would need to be scaled up to match it's resolution.

If you do not use a 1/2 scale ratio your luma and chroma pixels will not match pefectly so it wouldn't be a real 4:4:4 but an interpolated result.

At one point I heard a rumor that the Europe DVCpro HD specs were going to allow 1440x1080 since there is a lower framerate there is extra bandwidth to play with. I'm not sure if that is true or not but it would be nice.

I appreciate your responces. I'll run some tests via the software trials.
Will be using a switcher. Any recommendations on a good one?