Diirect-Recording component out to create clean key

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dvxStephen

Active member
I'm trying to shoot 4:2:2 or better high quality green screen footage without having to rent a Digital Betacam or SDX900 or the like. I've had a brainstorm of -- maybe -- an affordable way to do this:

The Sonys have component out. If I recorded that direct to tape or disk (ignoring the Sony's internal VCR, and using an external deck or recording direct to computer, via component inputs), would I bypass the Sony's compression scheme? Or are the component jacks, when the camera is in record mode, already outputting that nasty compressed video?

Also, anyone know if the output from these jacks varies with the recording format on these cameras? That is, if recording at DV vs HD, etc?

Thanks,

Stephen Gagne
 
The component outputs should avoid the MPEG compression entirely. And while I don't recall specifically, it certainly would make sense that the output would change based on which mode you were shooting in (i.e., NTSC component video when shooting DV, HD analog component when shooting in HDV).

The question about color sampling is, as far as I know, not answered. While the analog output will avoid MPEG compression, will it still be 4:2:0? I don't know at what phase of the process the color decimation to 4:2:0 occurs. If it's early on, then you'll still be getting the equivalent of 4:2:0 out the analog ports (although perhaps chroma filtered). If all internal processing happens at 4:2:2 or 4:4:4, and the color decimation happens right before the MPEG compression, then the analog output could contain a higher color sampling frequency, and it could give you what you're looking for.

But I don't know that anyone's verified that, one way or the other.

There are two types of compression going on: analog compression (chroma decimation) and digital compression (MPEG-2). The analog outputs will avoid the MPEG-2 compression. The question is whether they'll avoid the analog compression.

The other challenge you'll have is -- how do you intend to record the analog signal? You'll need an HD-SDI converter and an HD-SDI capture board, or an analog component HD capture board, and a RAID of hard disks that can sustain at least 166 megabytes per second of sustained transfer rate, plus the appropriate software, plus enough storage to capture the footage you need... capturing uncompressed high-def footage is not an inexpensive proposal.
 
Barry,

Thanks for your thoughts.

"...how do you intend to record the analog signal? You'll need an HD-SDI converter and an HD-SDI capture board, or an analog component HD capture board, and a RAID of hard disks that can sustain at least 166 megabytes per second...."

I had a much simple plan, assuming I can get it to work. Panasonic's new AJ-SD225 deck has component inputs and records DV50. I'm assuming this means I could attach it to the Sony camera, and if the component signals are clean, get a key that at least approaches the quality of the SDX900's DV50's. I realize the Sony falls short in terms of lens quality, and the third inch chip also limits things, but I'm thinking it should still be a great way to get affordable 4:2:2 keyed footage, that is in the same quality league as the DVX100a and XL2 output to MiniDV25 tape when not attempting to key. (We're using those 2 cameras for the rest of our footage when not working green screen.)

This deck might also be useful later on for archiving and maybe even live recording DV50 footage shot with Panny's new HDX200 camera once that comes out, particularly while we're waiting for the cost of P2 cards to drop.

If this sounds reasonable, I guess the question is, how would one find out if the Sony component output is before the analog compression scheme?

Thanks,

Stephen
 
Ah. So you're not talking about using its HD capabilities, but wanting to do it in SD?

Hmmm. Interesting.

Well, you couldn't put the camera in HD mode because the component outputs would be outputting an HD signal, which the deck wouldn't be able to record (guessing here, haven't tried it). So presumably you'd be operating in DV mode.

I guess you'd have to test it. If you've got an FX1, and a decent-quality television with component inputs, then one way you could test it is to use an injket printer to make a solid green sheet with thin red lines through it, and shoot that live with the camera, and view the output on the component (preferably LCD) monitor... if you get nasty blocky artifacts around the diagonal lines, that means it's post-chroma decimation. If it's sharp and clean, that might mean pre-chroma decimation.

Totally guessing here, as I haven't tried this.
 
Very cool idea. Unless someone else knows the answer (or the # of the sony tech rep that might!) I'll do this test sometime in the next few weeks.

Thanks, Stephen
 
Thanks, Anhar. No intrusion!

I looked at their posts.

So this might suggest the following workflow: For greenscreen work in project that's otherwise (that is, the non-green screen sections) being shot DV25 24p, shoot greenscreen scenes with the Sony at HDV, key the matte in post on an HDV timeline, and then convert the resultant keyed footage to 24p SD resolution.

I wonder how that would compare to shooting greenscreen in 4:2:2 in SD? Anyone know?
 
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