Keying with the Z1U

[Daniel Broadway]

Hey guys, two quick questions.

1: Is there a way to remove the MPEG compression artifacts with any kind of filter. It's making keying almost impossible.

2. How good does SD footage look from the Z1U. I don't hear alot about this particular aspect of the camera.

[Boyd Ostroff]

I doubt if those artifacts can be removed, but maybe someone else will have some ideas.

Actually there has been quite a bit of discussion regarding the Z1 in DV mode and also downconversion in-camera. I haven't been working directly with HDV yet, but have done a lot of SD work with my Z1 in both PAL and NTSC mode. I'm really happy with the results. I think you get superior results by shooting HDV 1080i and downconverting the firewire output as opposed to shooting in DV mode. However you will completely avoid the MPEG artifacts if you just shoot DV mode.

Another thing you might look at is shooting in HDV 1080i and setting component downconvert to 480p. This seems to give really sharp results - on my 1280x768 Sony 17" LCD monitor I could hardly tell it from HD. You can't send this progressive output over firewire though, just through component so you would need a capture card or firewire converter box.

[Augusto Manuel]

Boyd: the firewire converter box, will it take the component out of the Z1 and convert it to firewire so it can be digitized. If so, I would assume it will also have an audio input along with the component inputs. And if so, who makes it, and how much? Or am I totally wrong?

Originally Posted by Boyd Ostroff

You can't send this progressive output over firewire though, just through component so you would need a capture card or firewire converter box.

[Douglas Spotted Eagle]

As far as I know, all boxes that can manage component in, can also manage audio input. I've yet to see one that can't.
Convergent Design's HD Connect box, HD Connect LE, will do this, so will the Decklink Multi-Bridge, except it doesn't have firewire anything on it. (I just bought one last week, very impressed)
Miranda's does have firewire, and component in, plus audio, of course.

[Boyd Ostroff]

I haven't used the ADS box, but here are the specs:

http://www.adstech.com/products/API-...sp?pid=API-555

Audio capture in 48, 44.1 and 32 kHz (12 and 16 bit)

[Daniel Broadway]

Well, I want to shot in HD, and downconvert to 853x480. I thought that would eliminate the MPEG compression. But after doing this with footage online, the MPEG compression artifacts are STILL there.

[Boyd Ostroff]

I was out earlier today and passed by CompUSA.... I couldn't resist the urge to stop by and pick up one of those ADS Pyro capture boxes. I'm going to try some tests capturing footage from the component outputs set for 480p and will post some examples soon.

Daniel, why would you resize to 853x480, is this something you're going to stream on the web maybe? That isn't really a valid size for DV footage. 16:9 anamorphic DV is 720x480. On playback your monitor stretches it out to the equivalent of 853x480.

Regardless, I would expect different results from capturing the Z1's progressive component output than you got by playing around with online footage.

[Daniel Broadway]

Yes, I know it's not a valid size. However, I will be adding lots of visual effects before hand and I need to work on a native 16:9 shot.

One thing I don't understand is that the other day when I ripped some footage from a DVD, I converted the VOB to AVI using VirtualDub. When I looked at the color space, it looked like it was 4:4:4. I thought it would have all sorts of horrible artifacts since DVD footage is stored as 4:2:0

[Boyd Ostroff]

OK, I just hooked up the ADS Pyro capture box to my z1 via component and set the camera to downconvert to 480p. Long story short: it doesn't work. The Pyro can't lock onto the 480p signal and I get a variety of changing weird things, like 4 little messed up images, or a larger one that's tearing apart.

Now if I switch the z1's component output to 480i then the box works as expected. So I captured the same short clip with the Pyro box, and directly from the z1's i.Link port using HDV > DV downconversion. There's a big quality difference between the two. The 480i component video captured by the Pyro is much, much noisier than the z1's downconverted DV.

Clearly the problem is coming from the noisy capture circuits in the Pyro box; if I connect the z1's 480i component output directly to my 22" Samsung 1280x720 LCD screen it looks far better than it does when I play the captured component video on the same screen (using firewire > component transcoding on my DVD recorder).

So my hope for a cheap way to get 480p into the computer was just wishful thinking I guess :-) Too bad, if I play the 480p component output to that same 22" LCD screen it really looks much better than 480i. I can hardly tell it from the 1080i component video.

Oh well, the Pyro goes back to CompUSA tomorrow...

[Daniel Broadway]

Boyd, if you won't mind, could you post a few frame grabs of the 480i signal that you captured. I'd like to inpect the frames myself. If you could post a tif or targa, that would be great.

[Boyd Ostroff]

Here you go. These are unaltered frame grabs from FCP, exported as TIFF with best depth. The source footage was a slow tripod mounted pan.

1080i HDV output as 480i component and captured with the ADC Pyro AVlink: http://greenmist.com/hdv/component.tif

1080i HDV output with i.Link downconversion to DV and captured via firewire: http://greenmist.com/hdv/firewire.tif

The noise is more apparent in the moving image. But even if the component capture were of equal quality, there wouldn't be any point to capturing 480i component video. 480p would be worth the effort. And of course when you capture through a device like this there is no timecode so you can't use batch capturing.

[Daniel Broadway]

Thank you very much. I will be inspecting these grabs, as well as some footage online. I will let you know how my work came out.

[Augusto Manuel]

Thank you anyways for trying. After seeing the prohibitive costs (at least for me) of the Miranda and other converters, it would have been a blessing if that would have worked for you. I would have bought one myself also. Thanks anyways.

Originally Posted by Boyd Ostroff

So my hope for a cheap way to get 480p into the computer was just wishful thinking I guess :-) Too bad, if I play the 480p component output to that same 22" LCD screen it really looks much better than 480i. I can hardly tell it from the 1080i component video.

Oh well, the Pyro goes back to CompUSA tomorrow...

[Daniel Broadway]

Alright guys, I ran extensive tests last night involving HDV footage for keying.

Here are the results:


1. HDV is fine for keying low motion shots, such as interviews or whatnot. The MPEG blocking is very minimal in these shots, and they key well.

2. HDV is almost unacceptable at keying high motion scenes, such as shooting a fight scene at a standard shutter speed. MPEG blocking around punches or kicks is WAAAY to high. Also, weird artifacts surface around actors motion blurred body parts when shot on greenscreen. A grey halo appears.


3. I have not tested fight scene footage against bluescreen. It may not exibit the same artifacts.

4. But overall, HDV does not key well, even worse than DV it seems. Perhaps at a higher bit rate, this would not be a problem. Say at 50mb or 100mb.

[Boyd Ostroff]

Originally Posted by Daniel Broadway

overall, HDV does not key well, even worse than DV it seems.

If you downres it to DV how do the keys compare? The in-camera downconversion on my Z1 looks quite good to me, better than my VX-2000 or PDX-10 images. Have not looked at high motion sequences carefully though.