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Old July 17th, 2007, 02:29 AM   #16
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Quote:
Originally Posted by John X. DeMaio View Post
...and it is only a 50M/bit codec. Better than XDCAM's old 35M/bit but no where near as good as DVCPROHD 100...
Sigh! Just to dispel a few myths:

1. Interframe codecs (XDCAM HD) are about 2-3 times as bitrate efficient as intraframe codecs (DVCProHD), so straight numeric comparisons don't show anything other than how much hard drive space is required to store footage!

2. DVCProHD only uses 100Mb/s on 1080i.

3. XDCAM HD has a higher luma resolution than DVCProHD.

4. XDCAM HD has a higher horizontal chroma resolution that DVCProHD.

5. I've never had a problem with an image actually breaking up using 35Mb/s XDCAM HD.

6. Extreme motion is to XDCAM HD what extreme detail is to DVCProHD. You may get softening of the image as the codec runs out of bandwidth.

7. Your own mileage may vary...
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Old July 17th, 2007, 06:18 AM   #17
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Originally Posted by Alex Leith View Post
1. Interframe codecs (XDCAM HD) are about 2-3 times as bitrate efficient as intraframe codecs (DVCProHD), so straight numeric comparisons don't show anything other than how much hard drive space is required to store footage!
Under ideal circumstances, yes. Under less than ideal circumstances, where the interframe codecs break up, there's no comparison possible because the intraframe codecs don't/can't break up.

Quote:
2. DVCProHD only uses 100Mb/s on 1080i.
Not true, it's 100Mb/s on 720/60p as well. And 720/50p.

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3. XDCAM HD has a higher luma resolution than DVCProHD.
Not true in PAL, they're both 1440x1080. XDCAM is a tad higher in luma in NTSC, but not in PAL.

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4. XDCAM HD has a higher horizontal chroma resolution that DVCProHD.
Not true in PAL; in PAL they have the same horizontal chroma and DVCPROHD has twice as much chroma vertically. In NTSC XDCAM has a tiny advantage in horizontal, and DVCPRO-HD still has twice as much vertically. No matter how you slice it, DVCPRO-HD has extremely more chroma information than XDCAM-HD.
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Old July 17th, 2007, 07:18 AM   #18
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John,

Thank you very much for sharing your NAB observations. Jan is very accommodating. I'm glad she was able to get you that HPX500 footage.

What kind of projects are you shooting with the HPX-500?

Thanks again.
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Old July 17th, 2007, 07:33 AM   #19
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Originally Posted by Barry Green View Post
Under ideal circumstances, yes. Under less than ideal circumstances, where the interframe codecs break up, there's no comparison possible because the intraframe codecs don't/can't break up.
I accept that intraframe codecs don't fail catastrophically (like interframe codecs can), but catastrophic failiure is extremely rare. Personally I've never had a problem on 35Mb/s XDCAM HD even on fairly extreme motion. And in shots with extreme detail but little motion (forests, for example) you do see macroblocking and image softening on DVCProHD.

What I'm saying is that both codecs have limitations. Neither magically capture everything in perfect quality, both make compromises in image quality - just in different areas.

Anyway, if intraframe codecs were inherently flawed, then would Panasonic be adopting them on their future products?

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Originally Posted by Barry Green View Post
Not true, it's 100Mb/s on 720/60p as well. And 720/50p.
Yes, acknowledged... being in Europe I forgot about 720p50/60 (no-one broadcasts that over here).

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Originally Posted by Barry Green View Post
Not true in PAL, they're both 1440x1080. XDCAM is a tad higher in luma in NTSC, but not in PAL.
Yes in PAL, but 1440 vs 1280 is perhaps more than a "tad"?

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Originally Posted by Barry Green View Post
Not true in PAL; in PAL they have the same horizontal chroma and DVCPROHD has twice as much chroma vertically. In NTSC XDCAM has a tiny advantage in horizontal, and DVCPRO-HD still has twice as much vertically. No matter how you slice it, DVCPRO-HD has extremely more chroma information than XDCAM-HD.
I know from experience that it's not as clear-cut as you make out. As you correctly say DVCProHD has slightly lower horizontal chroma sampling at 30/60fps, but improved vertical chroma sampling, with a chroma samples in 2 x 1 blocks vs XDCAM HDs 2 x 2 blocks (with Cb Cr on alternate lines).

Does double the vertical chroma sampling double the image quality? I'd say not. There is actually very little perceptive difference to the colour quality of the images. The eye is about half as sensitive to color "resolution" as brightness. In my opinion the reduction in luma (in the NTSC variants of DVCProHD) has a more significant impact to image quality than the reduction of chroma in XDCAM HD.

As to the oft-sited improvements for chromakey work doesn't hold much water too. I have had not found particularly better / cleaner keys from DVCProHD over XDCAM HD when working with progressive footage.

There is certainly an advantage to DVCProHD when working with Chromakey work with interlaced footage - but personally that's not something I 'd work with, so I can't comment. (Almost all my work is progressive).

Anyway, I'm not arguing about the quality of DVCProHD. It's a great looking codec and I use it almost as much as I use XDCAM HD. What I am arguing with is the idea that XDCAM HD is inferior to DVCProHD simply because it has a lower bitrate.
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