Home Made HD Cinema Cameras - Technical Discussion

[Jason Rodriguez]

Hi Steve,

Another question. I saw this in the brochure:

Sub-sampling Readout

Subsampling can be used to readout fewer pixels in the imager at increased frame rates. Four subsampling modes to provide 1.5X, 2X, 3X and 4X lower resolution as shown (1280x720 @ 120 fps, 960x540 @ 240fps, 640x360 @ 540 fps, 480x270 @ 960 fps). Due to the use of bayer patterns, only the 3x subsampling cab be used to produce a color image.

What does it mean that only 3x can be used for color images? Does that mean that the 720p version will only be in monochrome-I thought I'd heard otherwise. Either that, or I had thought we wouldn't have to resort to windowing to get 720p, thus reducing the effective optical size of the sensor.

Thanks.

[Rob Scott]

Jason Rodriguez wrote:
I'm wondering if the problem becomes once you clock the chip too high, you can't get the shutter speed down (but you have reduced rolling artifacts), and you get what I call the "Saving Private Ryan" effect of a really jerky, shuttery camera image from too fast a shutter that doesn't allow enough motion blur (albeit with reduced rolling shutter artifacting).

If you can get the equivalent of 48 fps, you should be able to skip every other frame to get the equivalent of 24 fps with 1/48 sec exposure.

If you could get 96 fps (as you could with the AltaSens @ 720p), then I wonder if you could "average" two -- or four -- frames together ... ? This would reduce the rolling shutter artifact and (I think) give the right amount of motion blur as well.

What does it mean that only 3x can be used for color images?

I was wondering the same thing thing -- as I recall, Steve said that AltaSens had a 720 mode that used binning and used the entire chip in a "higher sensitivity" mode; and was still a Bayer pattern, albeit a somewhat odd one. At least, that's what I think he said.

[Jason Rodriguez]

Yah, I'm a little confused myself since I know that JVC is using these chips in their new 3-chip "broadcast quality" HDV camera, but the specs on that camera are 1280x720-so you can use the Atasens 3560 at 720p, but I'm not sure what the size of those chips were (if it's windowing, then the effective optical size becomes a 1/2" rather than 2/3").

[Rob Scott]

Jason Rodriguez wrote:
if it's windowing, then the effective optical size becomes a 1/2" rather than 2/3"

What I recall is that it does row skipping/binning to get 720p at the full (2/3") size of the chip.

[Steve Nordhauser]

Jason on Subsampling:
You are correct about the binning mode - it is only useful for monochrome sensors - I was wrong about the reduction. I'm not sure but I think you might be able to create a new Bayer interpolator for the 2/3 format (getting you to 1280x720 subsampling so at 2/3"). Row 0 is RGGRRGG. The next row is GBBGGBB. Then a row is skipped so the next is blue again, and then red.

Jason and Rob on rolling shutter:
There is usually a programmable horizontal and vertical blanking time. On the SI-1300, that can be set to a full frame time. This means that it is possible to set the clock for 60MHz, extend the vertical blanking to get the readout+blanking time to be equal to 1/24th sec. You should be able to expose during the blanking time (this is just a non-readout time). Since the readout happens very fast, you get minimal RS artifacts. Of course you also get a 60Mpix/sec bus load which will be too fast for 32 bit machines (2 bytes per pixel unpacked) but you could drop to 50MHz and set it up so a frame is moved to memory and then to RAID during the blanking time.

[Wayne Morellini]

Steve, thanks for answering that here.

The 1920HD PDF that Steve posted earlier has the examples of the 2/3 process.

The process should be suitable for 720p conversion using the standard bayer filter.

720p bayer pattern after skipping:

GR-RG-GR
BG-GB-BG
---------
BG-GB-BG
GR-RG-GR

- Is the skipped pixels in the bayer pattern.

The combining process would result in the pattern seen in the PDF.

[Wayne Morellini]

I am wondering,we have motherboards that can take between 4 and 8 GB of memory which is around two minutes of bayer 1080 footage. Maybe we can save money by using Rob's idea of saving out during pause aswell. We could then use slower cheaper higher capacity single/double consumer drives (you will need lots of them for a movie).


Thanks

Wayne.

[Wayne Morellini]

Another interesting article on using GPU programming for audio processing.

http://www.tomshardware.com/hardnews...02_135943.html

http://www.bionicfx.com/

Re-edit:

I seem to have found an article that says that the AGP backchannel is 266MB/s peak, more than enough to save out a comrpessed SHD stream (but the card/chipset architecher would have to be built to take advantage of this, ie. it could even be as slow as 32MB/s in some real life cards). Still PCI-E should be better.

http://graphics.tomshardware.com/gra...0/pcie-09.html

http://developer.nvidia.com/object/General_FAQ.html

On high 3D card power requirements. We don't nessacarily need to use the latest and greatest GPU, even a low powered integrated one might offer enough performance assistance.

Thanks

Wayne.

[Wayne Morellini]

Here is something more interesting than relevant to us (only has HD component in). High DEF (3D I think) PVR with full Intervideo suit.

http://www.via.com.tw/en/Digital%20L...niC-Club3D.jsp

http://www.s3graphics.com/pressrel/2004_06_03.html

http://www.club-3d.com/en/club-3D.html

[Wayne Morellini]

Wooh Hoo, Wooh Hoo (thats sarcasm, I'm not that big of a Oprah fan). The new Sony HDV camera is finally here (on time not liek all those people saying it would be next year). Now, maybe, they will ALLOW, JVC and Sharp to release their new HD cameras. Got to read the specs, but I doubt it will allow raw output.

http://www.camcorderinfo.com/content...-Camcorder.htm

Quiet an improvement over the pd170, but In comparison to our project, the camera looks hobbled, the article says 960*1080 pixel chips, but has 3 lux performance.

[Rob Lohman]

No HDV camera will ever output RAW. That's not in the HDV spec,
nor in the DV spec. Not to mention how they would store it anway.

Personally I don't see how an MPEG2 stream is going to be the
future of HD(V). But maybe I haven't been converted yet <g>

[Wayne Morellini]

Sorry I have taken so long, I was going to re-edit that but the machine crashed in the middle of it.

It was a bit of a joke, but since we have started this project we have seen an unconfirmed report of a $2K 3CCD JVC HD camera, now this cheaper price of the Sony to $3700, which is just enough to discourage people from a project like ours, it is tempting to think we are getting too them ;) If we are successfull then they will need to include raw connections in future to keep people away from us.

I'm just including this as a comparision to our cameras.

[Rob Lohman]

Thought so Wayne, just wanted to make sure <g>

[Obin Olson]

guys I hate to burst your bubble that has been floating about for some time but that JVC camera is $20,000 not $2,000

[Wayne Morellini]

Finally got around to phoning JVC america today (no response by email in past), and got some guy on the phone, who thought his computer screen was an oracle or something, no mention of the camera, couldn't even ask him who I could speak to about it, or send him a link to his site that proved the camera existed. I had to explain, to him, that I might aswell just leave it until it was released, as it was probably preliminary information and the camera was most likely delayed (but went in one ear and out the other). Spent a few hours googling aswell, and nobody else has a price listed, even the shop companies with the camera listed.

So nobody has gotten a confirmation on the price in the video systems article, except for my post about asking a local Australian agent, who thought the $20K I suggested was more likely (but still knew nothing).

Somebody started a new thread about a 1024*768 CCD Sony Box camera with capture software, and firewire, for around $1.5K, thats getting pretty close. So maybe the big guys are catching on, and trying to stramp out all the effort we have invested in these cameras. As long as they aviode a HD resoltion 3 chip camera, Sony can feel reasonably confident in talking a pro customer into spending a lot more on a HD spec camera, or buy the inferior box camera.