Using an ex for greenscreen

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Michael.Bradshaw
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hello,

A friend has a sony ex and a reflectmedia green screen kit. he is having trouble getting a decent key as some of the subject is keying out.

We were wondering is it the color sampling making it difficult and if so would it be better to capture directly to the computer using the sdi output into a black magic card etc. I think the ex uses 4 2 0.

Any opinions or ideas on a better method would be appreciated.

michael.

EVGA sr-2/ 2x x5850 win7 x64. Editing in Ppro CS5 Shooting on Sony Z7, nex-VG10

Alan Roberts
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You say "using the sdi output", does that mean you're using the camera to shoot SD not HD? If so, then you'll certainly have problems because the camera's doing as down-conversion from SD to HD. There is no HD camera on the market, at any price, that does a good down-conversion, they all leave aliasing in the picture.

I haven't tested the EX yet, Sony have asked me to do it, and I'm trying to set it all up, but I'm falling foul of the impending move of BBC R&D, so it's getting hard to fix.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Michael.Bradshaw wrote:
We were wondering is it the color sampling making it difficult ........ I think the ex uses 4 2 0.

Difficult to say too much without seeing exactly the problem, but I would be very, very surprised if colour sampling is an issue. Any difference it would make would be on quite a fine scale, and you sound as though you're talking about something more fundamental here?

Most keying problems are a result of lighting etc issues, or insufficient separation from the foreground. Has your friend had good keys from the same setup with a different camera, or is everything new?

As regards 4:2:0/4:2:2 it's worth remembering they are only ratios of luminance/chrominance samples, not absolute numbers. Since the EX records more luminance pixels/frame than most other formats, the no of chrominance ones is increased as well, so 1920x1080 luminance, 960x540 chrominance. Compare that to HDCAM - 1440x1080 luminance, 480x1080 chrominance (it's 3:1:1). Being progressive or interlace also makes quite a lot of difference, and 4:2:2 really came into being when video meant interlace - an unsymmetrical system meant an unsymmetrical colour sampling made sense. Progressive means H&V symmetry, and 4:2:0 is a symmetrical system.

Christian Lett
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Joined: Apr 26 1999

Michael,

How is your friend doing the key? In post using software like AE, or real-time using the hardware solution?

Getting a good key is difficult, but perfectly possible with 4:2:0 footage. Unfortunately it's never quite as simple as just a single click with a chroma-key plugin. I usually pull two keys (edge and core), do a bit of roto for garbage mattes and other fiddly areas, spill suppression, colour correction, edge blurring and a bit of light-wrap to get the person looking like they belong in the shot! I'd be surprised if you couldn't get excellent results using the EX1.

C

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

Michael.Bradshaw
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Joined: Aug 1 2005

he's keying it out in final cut. I still think it's one of the best keys I've seen and maybe we expecting too much. I'll see if I can get some gras off him and stick them up to see if you have suggestions about lighting.

Alan, I was just wondering if capturing standard def using the sdi output would have given an advantage? I didn't realise the downconversion would casue issues but I'll get some images and maybe you guys can tell us if it's down to the codec or if the scene needs lit differently.

Thanks, Michael.

EVGA sr-2/ 2x x5850 win7 x64. Editing in Ppro CS5 Shooting on Sony Z7, nex-VG10

Alan Roberts
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In theory, you should get better results shooting HDV and downconverting after compositing. It all depends on how good the camera's downconversion is, which I can't comment on until I've done tests.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Joined: Jul 18 2003
Alan Roberts wrote:
In theory, you should get better results shooting HDV and downconverting after compositing.

I'm sure you meant to say shooting XDCAM-HD, Alan.........? ;)

Alan Roberts
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Actually, it was a different slip, I should have said "shooting HD" :)

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

fuddam
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Joined: Nov 19 2005
Michael.Bradshaw wrote:
I'll see if I can get some gras off him and stick them up to see if you have suggestions about lighting.

my mama told me to stay away from drugs

:(

Michael.Bradshaw
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Joined: Aug 1 2005

no, no, no.

"some grabs"

EVGA sr-2/ 2x x5850 win7 x64. Editing in Ppro CS5 Shooting on Sony Z7, nex-VG10

StevenBagley
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Michael.Bradshaw wrote:
We were wondering is it the color sampling making it difficult and if so would it be better to capture directly to the computer using the sdi output into a black magic card etc. I think the ex uses 4 2 0.

I took delivery of my EX1 yesterday, and did some filming out of the box while at work at my University's research showcase yesterday afternoon. Anyway, there were several blue noticeboards about and when I got home I tried CSOing onto one of the boards.

Let's say that just using the in built tools in FCP I was able to get nice results easily, although I was using GRaeme Nattress's colour resampling plugin (which takes 4:2:0 and upscales it to 4:4:4) to reconstruct the chroma. Going by past experience keying DVCam footage, I suspect that you'd get excellent results off the card in Shake or AE.

Obviously, the SDI out will be better but more complicated -- my advice would be (if you have the option) shoot to both SxS and SDI and do a comparison.

Alan Roberts wrote:
I haven't tested the EX yet, Sony have asked me to do it, and I'm trying to set it all up, but I'm falling foul of the impending move of BBC R&D, so it's getting hard to fix.

Ahh, I was going to ask you about that :)

It's a lovely camera, even out the box without reading the manual (or being able to find the white balance button!) I managed to produce some of the nicest footage I've ever shot ;)

Steven

Rob James
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Joined: Jun 26 2001

Alan, you wouldn't believe how many people are waiting for your analysis. I sincerely hope you manage to get it all together soon. The fact that Sony want you to test it seems significant of itself.

Rob The picture is only there to keep the sound in sync

StevenBagley
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Rob James wrote:
The fact that Sony want you to test it seems significant of itself.

Well I suspect Sony have an ulterior motive :) They want the BBC (et al.) to buy and use the thing in force...

Steven

Rob James
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StevenBagley wrote:
Well I suspect Sony have an ulterior motive :) They want the BBC (et al.) to buy and use the thing in force...

Steven

With Alan's reputation for impartial testing that would be a risky strategy unless it really is the dog's whatsits at the price.

Rob The picture is only there to keep the sound in sync

infocus
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Joined: Jul 18 2003
Rob James wrote:
With Alan's reputation for impartial testing that would be a risky strategy unless it really is the dog's whatsits at the price.

I doubt they have a lot of choice, since I doubt the BBC would use it (or anything else) without such a test.

As far as they are concerned it may fall into a slightly strange niche - expensive for the next generation PD150, Z1 etc, but not quite up to Digibeta/DSR500 etc sector.

StevenBagley
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infocus wrote:
As far as they are concerned it may fall into a slightly strange niche - expensive for the next generation PD150, Z1 etc, but not quite up to Digibeta/DSR500 etc sector.

It's expensive for SD, but not for HD. As an HD B Camera (to a 750 or HDX900 etc), it'd make a lot of sense -- although I wouldn't be surprised if it gave the HDX900 a run for its money in the resolution stakes.

The sticking point at Auntie as far as I'm aware is the worry about whether 35Mbit/s MPEG2 will hold up through the whole transmission chain. Although the switch from HDCam to HDCamSR delivery should help in that respect.

Steven

Alan Roberts
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Correct, the issue i the compression artefacts at 35. EBU tests have rejected it so far. But I believe the BBC's interest would be in it as a second camera, HDSDI connected to a decent recorder, possibly locked off (e.g. as a PoV camera) they wouldn't accept the 35M MPEG as the primary HD recording.

I'll poke the system again.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Joined: Jul 18 2003

But heck, we're talking about a "B" camera here, and I find it somewhat surprising that having seen PD150s, then Z1s, used quite extensively by Auntie for a number of years that come HD there is a seeming bigger problem with the EX? Or is the thought that it will become even more mainstream than Z1s are currently? Codec issues apart, at least it has 1/2" chips and a true manual lens, which to me puts it on a far higher plane than such as the HVX200 or Z1.

And if 35Mbs as used by the EX is considered a problem for unrestricted use, has the bar been set at any defined rate? 50Mbs? So does the PDW700 then take on a lot of interest?

StevenBagley
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infocus wrote:
But heck, we're talking about a "B" camera here, and I find it somewhat surprising that having seen PD150s, then Z1s, used quite extensively by Auntie for a number of years that come HD there is a seeming bigger problem with the EX? Or is the thought that it will become even more mainstream than Z1s are currently?

I think there is a strong desire to keep HD looking nice and not to let it droop to the low-levels SD production where cameras such as the Z1 are turning in sub-par pictures. Also, the PD150/Z1 are both used recording to DVCam not MPEG2, which should help.

Quote:
Codec issues apart, at least it has 1/2" chips and a true manual lens, which to me puts it on a far higher plane than such as the HVX200 or Z1.

Neither of them are suitable for HD acquisition though.

Quote:
And if 35Mbs as used by the EX is considered a problem for unrestricted use, has the bar been set at any defined rate? 50Mbs? So does the PDW700 then take on a lot of interest?

The BBC guidelines define not-HD as:

BBC wrote:
2.1. The following formats are considered to be standard definition:
o All standard definition video formats
o HDV from all manufactures
o Cameras with image sensors under ½”
o Frame based recording formats below 100Mbs
o Inter-frame based recording formats below 50Mbs
o Super16 film whether transferred to tape in high definition or not
o 35mm film transferred to standard definition tape formats
o Non linear editing codecs with bit rates below 160Mbs
o Live contributions via links at less than 60Mbs (MPEG2)

Although I'd have thought 'Frame based recording formats below 100Mbs' would rule the Varicam out (since at 25fps its bitrate is way below 100mbit/s)...

Steven

Alan Roberts
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Varicam gets under the door because it's the only truly variable speed camera around, so far, and because it still does the best impression of film. The extraordinary combination of controls lets me tweak it in ways that make sense, all praise to Panasonic for that. As soon as there's a decent alternative, Varicam will go, I reckon.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.