Saturday, September 17, 2005

So many new HD cameras to choose from, so much misinformation.

There is much heated discussion on the various HD and HDV forums regarding sensor resolution, compressed types and bit-rates of the new crop of prosumer HD cameras. So much is focused on these elements, yet the numeric data is often less significant than the quality of the lens and the physical size (not resolution) of the CCD/CMOS. This is encouraged as so much of the marketing of these cameras is rooted in the numbers -- three CCDs is assumed to better than one, chroma sampling 4:2:2 better then 4:2:0, and 100Mb/s is better than 25Mb/s, all seems so true, yet in most cases the impact of image quality is far more complex than that, with the numbers often hiding more significant characteristics.

What is the true resolution of a camera? Put a resolution chart in front of its lens and you have better information than any of the marketing data. However the ability to resolve detail will be impacted by the sensor resolution, physical pixel size, compression resolution and chroma sampling. I in the next few post I intended to go into interesting technical details on a range of these new cameras, pointing out where I think the marketing information based on the numbers are either misleading or significant to the final out image quality.

Here are the range of the sub-$20k HD cameras that are annouced or currently available.

Canon XL-H1
Grass Valley Infinity
JVC GY-HD100U
Panasonic HVX-200
Sony HVR-A1
Sony HVR-Z1
Sony XDCAM-HD

I intend to discuss a little on each. Please point out if I have missed any interesting new cameras.

4 comments:

HDTV said...

Hello David,

I would like to thank you for running this blog and helping us with understanding the technical matters in this new low cost HD production era. You, and the guy Frederic Haubrich? are the only two people I trust in these forums. Both of you stated, before the FX1 became announced, something to the effect that HDV has the potential to look better than Varicam. That makes sense, since Varivam's effective rate is only 40 Mbps at 960x720 recorded pixels.

What I find amazing is how cleverly Sony modified the MPEG2 compression to provide image quality that intercuts very nicely with 1080i HDCAM. You stated in one of the forums that the frame size on Z1 is between 150-500 kB. That indicates compression level between under 5:1 on no or minimal motion, and would indicate over 15:1 on very high amount of motion, if normal MPEG2 was used. What however happens is that the image softens up on motion, and when this softened-up image is compressed, we may end up with effective compression, from this softened up image, that is closer to 5:1 than 15:1.

This explains the excellent image quality, ease of color correction, because full or near full bit depth may be maintained. Anyway, the 150-500 kB translates to about 36-120 Mbps. 120 Mbps lies half-way between DVCPRO HD and HDCAM; that is on no or little motion.

What happens on motion is that the image softens up, which creates motion blur that may not look natural compared to film or HD, but our eyes lose resolution on motion too, so the result is pleasing and acceptable.

I have many questiuons to ask:
1. If the no motion effective compression on Z1 is inder 5:1, what is the effective compression ratio on high motion, from the softened up image?
2. Are all HDV cameras outputing 8 bit quality stream through their uncompressed output? You mentioned that the Canon is outputing 8 bit through HDSDI. If outboard HDSDI converter is used on uncompressed output of Z1, do we again get only 8 bit quality, although the converter outputs 10 bit? How about the JVC HD100 camera output? Do we get 720/60p at 10 bit depth?

Low light ratings: If we assume the Z1 as a refernce point at 3 Lux, is the DVX200 roughly 6 Lux and the HD100 roughly 12 Lux?

If one was to record from the HDSDI on the Canon XL H1, then for compression your Aspect HD would be sufficient. If any of these cameras have 10 bit output quality, then Prospect HD would definitely be the way to go.

Are there computers available that would record these HDSDI streams and would compress them on the fly and hopefully would allow HD monitoring at the same time? If no such low cost solutions are available, could you recommend best cost effectice configurations. A lot of filmmakers would be very interested in this, but you have to offer a finished product, or at least recommend very specific trested configuration; these people are not computer experts. The computers should be small, low cost, quiet, with low power consumption, hopefully with DC power input, and HDSDI input of course. What would be the cost? What would be the cost of Prospect and Aspect HD? Can the computer record multichannel sound at the same time? Can you recommoed a matching mixer with proper output and software?

Sony X310 POV camera already has HDSDI and HDV outputs. I think that the same camera head will be used on XDCAM HD. Is that camera's 1080/24p quality superb? Is there a loss of resolution on progressive? Are the chips switchable interlaced / true progressive?

From my experience, and from reports by others, 1080/50i, when properly deinterlaced, is overall equal to 720/25p, image quality-wise. Is that what you find?

From resolution charts I've seen, CineFrame 25 on Z1 has excellent resolution, although somewhat diminished compared to 1080/50i. This resolution lowers with motion. Does the interlaced resolution lowers on motion equally, or is it less? From what I have seen, the CF25 mode gives better resolution than 720p. Did you find the same thing? How is the deinterlacing accomplished? Is it done inside the MPEG2 encoder? If so, how is the 25p progressive motion achieved on the viewfinder? Is it by displaing one field only?

There is a new Panasonic #400 camera that is using the same progressive 720p chips as Varicam, but the European model variation records 1080/25p. I can see that there would be improvement over Varicam horizontally from 960 to 1280 pixels, unless of course there is vertical and horizontal shift on the chipset and then full 1440x1080 resolution would be available. What do you know about this camera?

Cine Alta is advertised as 1000 line horizontal resolution, I believe. Does it mean that vertical resolution is 1333 lines, or do they talk about 1000 lines before downsampling to 1440 pixels horizontally?

When shooting with Z1 for film out, is it better to use CF25 or to deinterlace later with DVfilm?

Does Matsushita make the HD100 CCD chipset? Who makes it for Canon? Is Sharp going to enter the HDV market? What do you think; will there be just one HD DVD format released; will Toshiba yeeld for royalties from Sony?

The 35 Mbps on HD XDCAM -- what kind of improvement in image quality can we expect compared to HDV?

How does Canon F25 resolution compare to Sony CF25? Is HDV1 24p effective bit rate 20 Mbps, or is there a pull down used? How about F24 o Canon?

Infinity camera will have 1080i and 720p. Will these be 10 bit? For film out, would better quality be achieved shooting 720p, or using best deinterlacer on 1080i?

The Infinity codec, JPEG2000, or something, how good is it?

Your codec is wavelet, or somethign like that, based? What does it mean?

What is the GOP on Aspect and Prospect HD?

Hope you answer ate least some of my questions.

Again thank you very much for your services to the community and for keeping your integrity in a field of salesmen posing as technical geniuses.

David said...

So many questions. :) Maybe you could re-ask one at a time on DVInfo.net.

ReBirth Cinema said...

I've ask just one okay David!

The HD analog component out on the HD100 - is it 8-bit or 10-bit? Thanks so much if you know the answer!

ReBirth Cinema
www.cine.ma

David said...

Analog is neither, as it is analog, not digital. :) I don't know what precision it is derived form. In any case it is best to digitize the results in 10-bit.