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Old January 18th, 2006, 11:56 PM   #1
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DV upconversion via SDI ??

Hi all -- I'm beginning to edit my documentary and in talking with potential editors, was told I should consider capturing my DV25 footage using SDI to reduce the jaggies and get a better quality image for festival screening. This is the second time this week I've been told that capturing via SDI reduces the DV25 artifacts.

I understand that SDI is an interface so what they're talking about is probably a result of upconverting DV to HD and then transferring via SDI.

Can comparable results be achieved by upconverting at the end of the project? Thanks a bunch for any advice offered.
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Old January 19th, 2006, 09:43 AM   #2
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I've heard some of this too and was very skeptical since minidv is the digital compressed stream, so I was curious as to how decompressing it in a deck and transporting over SDI would improved on an identical image.

Well, it kind of does and it doesn't. Mini DV is 4:1:1 so chroma is only sampled for every 4 pixels but SDI is 4:2:2, so chorma is sampled twice as much. What happens is that when converting the colour space in the deck it doesn't do a hard conversion when increasing colour space, rather it smooths it out, so even though the chroma pixels should be the first one is and the next one is an interpertation between the first and the second. So this smooths out the colour and reduces colour fringing in high contrast areas a bit.

Their is a plugin that produces the exact same effect to your minidv footage captured over firewire so you can achieve the same effect. I'll take a quick look for it.
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Old January 19th, 2006, 11:23 AM   #3
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Thanks, Keith! It makes sense about the color space resampling. I've yet to look at their footage, will probably get that chance this week and report back.

I assume it also does resolution interpolation as well (?) because the first person said it helped the color fringe (as you suggest) but the second person said it helped smooth out the stair-step jaggies and said the storage space requirements increase ten-fold!

What about an external box, like the Teranex mini?
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Old January 19th, 2006, 11:52 AM   #4
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I pretty sure it doesn't resolution interpolation because SDI (SDI is just standard def, HD-SDI is high def) is the same resolution as miniDV. 720 active pixels per 480 active lines. The chorma sampling is just different.

It can help with stair step jaggies (were all so technical here at dvinfo..hehe) with the same approach and they kind of mean the same thing. Certain jaggies get created by the chorma sampling of miniDV and although it doesn't appear the same as colour fringing its the result of the same problem - assuming I understand the jaggies your talking about.

As for stoarage requirements, well not quite 10 fold but close enough. The video portion of minidv is 25mbits/s, assuming you capture uncompressed SDI your looking at 720 x 480 x 30 frames x 2 channels (1 luma, 1 interleaved Cb Cr) x 8 bit = about 158 megabits/sec or 20 megabytes a second plus audio. So its a bit more.
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Old January 19th, 2006, 11:58 AM   #5
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I had a feeling it was someone on dvinfo that did the hard work on figuring this out - it was Graeme Nattress of course - how could I forget.

http://www.nattress.com/Chroma_Inves...masampling.htm
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Old January 19th, 2006, 01:17 PM   #6
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Wow! Outstanding work by Graeme Nattress !!!! Kudos to him, his article is well written and the photos and analysis are invaluable.

Okay, that clearly shows what you're talking about, thanks for referring me to his article, Keith!
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Old January 19th, 2006, 01:32 PM   #7
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Quote:
Originally Posted by Keith Wakeham
I had a feeling it was someone on dvinfo that did the hard work on figuring this out - it was Graeme Nattress of course - how could I forget.

http://www.nattress.com/Chroma_Inves...masampling.htm
Keith, I was going to post that same link. I read that article several months back and found it to be an invaluable source of information. In fact, I have pointed others to that link in several past threads here on DV-INFO.

Everyone should take a look at the link. It answers a lot of questions.

-gb-
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Old January 19th, 2006, 01:58 PM   #8
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I agree, and this question/topic will only become more popular. I did a search on this forum but didn't find the link mentioned, so let me add some potential keywords to this thread...

capture SDI upsample upconversion firewire fw conversion transfer chroma smoothing blockiness blocky color smear improve quality
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Old January 21st, 2006, 01:02 PM   #9
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259

SDSDI or SMPTE 259 requires 270mbps.
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