Single-chip 2k or 3-chip 1k camera?

[Martin Breidt]

I am wondering what system would produce better overall image quality in a computer-controlled camera setup for shooting faces:

a.) A single-chip 2k camera recording at 1080p60 with a Bayer pattern; the data would be stored on harddisk in raw format and de-bayering would be performed after recording

or

b.) A 3-chip camera at the same resolution, but interlaced (1080i60)?

I am not familiar with formats and protocols but I assume the 3-chip data will be converted to some slightly compressed format (4:2:2?) and transmitted to the computer through something like HD-SDI or HDMI

Any advise very welcome, I hope this forum is the right place to ask.

Thanks a lot in advance
Martin

[Bob Grant]

What do you want from the recorded data, still images or video and then what do you want to do with it.
In general progressive scan is easier to deal with in post or for analysis.

[John Bosco Jr.]

Since you are just shooting faces and considering the extra "de-bayering" process with the 2K, I have to say you're better off with the 3-chip 1080i camera. That is considering that you are recording uncompressed HD through HD-SDI. The uncompressed HD signal will be at least 4:2:2 if not 4:4:4.

[Martin Breidt]

Originally Posted by Bob Grant

What do you want from the recorded data, still images or video and then what do you want to do with it.
In general progressive scan is easier to deal with in post or for analysis.

We need video. In general short sequences of maybe 10 seconds or so.
I do not mind additional processing efforts, my main concern is picture quality.

Martin

[Martin Breidt]

Originally Posted by John Bosco Jr.

Since you are just shooting faces and considering the extra "de-bayering" process with the 2K, I have to say you're better off with the 3-chip 1080i camera. That is considering that you are recording uncompressed HD through HD-SDI. The uncompressed HD signal will be at least 4:2:2 if not 4:4:4.

Thank you. Do you have any recommendation on what kind of 'framegrabber' one would use to get the HD-SDI signal onto disk?

Martin

[John Bosco Jr.]

Originally Posted by Martin Breidt

Thank you. Do you have any recommendation on what kind of 'framegrabber' one would use to get the HD-SDI signal onto disk?

Martin

Framegrabber? Do you mean capture card? Anyway, It's depending on your system for compatibility.

I suggest either a Blackmagic Decklink Extreme: For under $1k you get 4:2:2 SD and HD SDI and analog inputs as well. You can step up to Decklink HD Pro for either PCIe or PCIx for up to $1.5k. This will give you 4:2:2 or 4:4:4 but only SD/HD SDI inputs (no analog). All the cards have digital and analog outputs.

Or AJA Kona 3: More pricy but will also capture 2k. SD/HD SDI 4:4:4 and 4:4:4:4 2k inputs (no analog inputs) for around $3K. You can get their budget card, which give you analog inputs also as well as 8/10 bit SD/HD SDI input for under $2k.

I believe the AJA cards are designed for Macs; whereas, the Blackmagic cards are designed for both, PC and Mac.

Note: all prices are estimates and are in U.S. Dollars.

Best of luck

[Martin Breidt]

Great info, thanks very much, John! And yes, capture card is what I am looking for. While we're at it, two more questions.. ;)

* What kind of harddisk array will be necessary to stream the SDI data onto disk?

* Is there any such capture card that can even handle two HD-SDI inputs?


Thanks again
Martin

[Bob Grant]

You're going to need a very fast SCSI disk array to handle 1080 at 4:4:4 and there's not too many camera that can output that anyway, the F350 can do it but that's very serious money. The XL-H1 and the Wafian recorder would get you 4:2:2 for under $20K, although it's arguable that the Xl-H1 is not exactly full 4:2:2 but pretty close.

All this aside though I wonder if you're not looking at this problem the right way around. I'd start by thinking about the image hitting the sensor(s) before I even worried about the sensor and the recording device. Unless you have a substantial amount of light and / or a pretty wide angle lens you're going to have significant DOF issues. Not much point recording pristine images if most or all of the face is out of focus. If you've got a wide angle lens then it's going to have to be pretty close to the subject or they'll not fill much of the frame which again looses all that the resolution has gained you.

Perhaps if we had a clearer idea of the entire purpose we could try to help better, you might even do better with a digital still camera and stobe lights than a video camera if say 4fps would be adequate.

[Martin Breidt]

Originally Posted by Bob Grant

All this aside though I wonder if you're not looking at this problem the right way around. I'd start by thinking about the image hitting the sensor(s) before I even worried about the sensor and the recording device. Unless you have a substantial amount of light and / or a pretty wide angle lens you're going to have significant DOF issues. Not much point recording pristine images if most or all of the face is out of focus. If you've got a wide angle lens then it's going to have to be pretty close to the subject or they'll not fill much of the frame which again looses all that the resolution has gained you.

Perhaps if we had a clearer idea of the entire purpose we could try to help better, you might even do better with a digital still camera and stobe lights than a video camera if say 4fps would be adequate.

This is for a custom-built, computer-controlled camera setup for scientific purposes for recording highres color video of faces. The cameras (the final system will use two HD cameras) will be in a fixed setup, about 1.5m away from the subject and run at 40 - 60 frames/sec, in sync with a strobe flash light. This is not about beauty shots of faces but about getting as much detail from faces as possible. So yes, indeed, depth of field is an issue and I was not aware that this would be so drastic as you describe it.

In terms of still photography, we are using a similar setup for still pictures with two Canon EOS 10D DSLR cameras at six megapixels and a 80mm lens (so with 1.6 crop facto, that corresponds to a 128mm lens on a standard 35mm SLR camera) and we get beautiful detail out of that.

Now I am trying to find a combination of camera, capture card and storage that will do this for video data with optimal quality (while not spending hundreds of thousands of dollars).

This thread was mostly about the difference in quality between a three chip system with lower resolution and a single chip system with higher resolution but bayer filtering. In the context of shooting faces. :)

Martin

[Bob Grant]

Thanks,
seeing as how you're currently doing this with DSCs ignore my comments about DOF. I was thinking trying to get images of faces as someone walked through a door or something similar.

All else being equal, same sized sensors, same number of pixels, a 3 CCD system will perform better than a single sensor. The issue you'll face is that it's rare for 'all else' to be equal. Also the single / 3 sensor design issue can be due to more than just image quality. The optics are different for single and 3 CCD sensors due to thhe prism. So designers usually will design a sensor system to work with existing optics as at the high end the cost of lenses can be much more than the rest of the camera.

Given your budget constraints anything overly custom might be out of the question. Sorry if I'm getting off your topic but I don't see this as a trivial consideration. For your application you're going to need cameras with genlock so you can sync to the strobe and keep the cameras in sync. And you'll need an affordable way of recording the images, getting real time video output would also be possibly helpful for checking alignment etc.

My suggestion would be two Wafian recorders which can record 4:2:2 from HD-SDI. Your choice of cameras would start with the Canon G1, then the XL-H1 then say the Sony F350. All of these are CCD camera i.e. global shutter, so stobe lighting should be fine. The Wafian guys should, if the units don't do so already, be able to offer record start / stop from an external input.

Only restriction I can see is the max frame rate will be 30fps. The Phantom cameras can do way higher frame rates and record to flash but the cost might be outside your budget.

[John Bosco Jr.]

Originally Posted by Martin Breidt

Great info, thanks very much, John! And yes, capture card is what I am looking for. While we're at it, two more questions.. ;)

* What kind of harddisk array will be necessary to stream the SDI data onto disk?

* Is there any such capture card that can even handle two HD-SDI inputs?


Thanks again
Martin

Hi,
As Bob indicated, you would need a SCSI array for 4:4:4, but for 4:2:2 you can get away with a g-raid (firewire 800 or 1394b - some computer systems do not have firewire 800 built in, so will need a seperate card) or even a SATA raid system.

As far as your second question goes, yes... two cards, actually two systems for two cameras. Unless you have a switcher and switch between the two cameras, you're going to need two systems if trying to iso the cameras and record simultaneously. I guess you could capture one camera at a time with one system, but if you want to record two cameras simultaneously, that means purchasing two edit systems. I like Bob's suggestion regarding the Wafian recorders. I suggest, then, to edit with final cut pro as it accepts the Wafian recorders natively. I'm not sure about other editing systems. The Wafian recorder is actually a capture and recording device, so no other capture cards or drives needed. Again for two cameras, you will need two recording devices if you're trying to iso and record simultaneously. The Wafian recorders don't come cheap, either, around $17k a piece. For the price of one Wafian recorder, you can get two final cut pro systems with the decklink HD supreme cards and a terabyte of g-raid storage for each.

If you don't mind shooting 720p, you can get 60fps from JVC's GY-HD250U. It would have to be the 250 as I believe the 200 does not have HD-SDI. Personally, I think the XHG1 or XLH1 like Bob suggested will suit your needs as far as cameras are concerned.