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#1 DOsborne

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Posted 06 April 2006 - 03:11 AM

Hi. I've grown confused while researching the HDCAM recording format. I originally thought that the compression ration was 4.4:1, but I've read in some places recently that it's 7:1? Also just to clarify the other specs are: 8-bit, 3:1:1 right?

If the compression is 7:1 why does HDCAM have a higher bit rate than DVCPRO HD? is it something to do with 1440x1080 vs. 1280x1080?

Lastly are there any opinions about how HDCAM holds up when printed to film? vs. DVCPRO HD?

Lastly for real, is there a very apparent difference between an image captured in HDCAM and HDCAM-SR, like with an SRW-1. 440 Mb/sec and 10 bit YUV seems like a huge step up, is it worth extra cost? Any thoughts are well appreciated. Thanks!
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#2 Phil Rhodes

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Posted 06 April 2006 - 05:56 AM

Hi,

> I originally thought that the compression ration was 4.4:1, but I've read in some places recently that it's 7:1?

It depends how you calculate it. Given that a 1920x1080x30x24, or 1424mbits/sec video stream (10-bit full HD at 24fps) represents what's coming off the chips and there's only about 140mbps going onto tape, you could quite easily argue that the compression is over 10:1!

However, when people say "compression" they're usually referring to the mathematical data reduction associated with techniques like discrete cosine transform and Huffman, and it's widely accepted that HDCAM uses DCT compression at around 7:1 after the VTR has performed downscaling and subsampling.

It's difficult to work out exactly where all the bits go. 1440x1080x13.3x24 is about 480mbps, representative of the HDCAM data stream after rescaling and subsampling, so it would appear that the format needs to compress at about 4:1 to fit its data into the available space.

> Also just to clarify the other specs are: 8-bit, 3:1:1 right?

Yes.

> If the compression is 7:1 why does HDCAM have a higher bit rate than DVCPRO HD? is it something to do
> with 1440x1080 vs. 1280x1080?

It's difficult to work this stuff out without a lot of inside information on exactly how they're doing it mathematically. However, the belief that DVCPROHD is less compressed than HDCAM is something of a fallacy - at 24fps, the DVCPROHD data stream is only 40mbps, less than DVCPRO50 in standard def. DVCPROHD records 1280x720, by the way, not 1280x1080.

Phil
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#3 stephen lamb

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Posted 10 April 2006 - 06:18 PM

Phil,
With the small amount of experience i have, i believe that DVCproHD can be either 1280x720 or 1280x1080. I have had film transferrd to DVCproHD and the information listed within the file itself, and what the lab claimed, both stated 1280x1080 (also how i brought it into FCP) Also, shooting on the HVX, i have shot images with a 1280x1080 image resolution....Having said that, the HVX's CCD is not big enough to actually have that much resolution...so i suppose it is sort of a moot point with the Uprezzing....or is it? Can anyone explain a bit "uprezzing"? Thanks, sorry that it is off topic a bit.

Steve
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#4 Elhanan Matos

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Posted 12 April 2006 - 02:42 PM

I think the 1280x1080 number comes from the way that DVCPRO HD stores ALL of it's 1080i material to save on bandwith and storage, just like they only record 960x720 when recording 720p, and just like Sony's HDCAM format records 1440x1080 for all 1080p.

What you must be doing if you are actually getting back material with a 1280x1080 resolution is using a pixel aspect ratio of something like 1.5 to bring the image back to a 16x9 aspect ratio.
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