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Old February 23rd, 2004, 10:55 AM   #1
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MiniDV resolution

Hi,

Does anyone here have in depth knowledge of the MiniDV format? I believe that generally speaking most DV cameras including the XM1 only record around 500 lines across the picture. Is this assertion correct? But when transferring via firewire the MiniDV spec is 720 lines across. Is this also correct?

If I had footage that was recorded on a higher resolution camera such as Digibeta etc, is there any way that such footage could be transferred over to MiniDV using the full 720 lines of the MiniDV spec (I realise of course that Digibeta will use 768 lines so there would still be some loss)?

Is the 500 line just limit of the camera CCDs while the tape is still recording an interpolated 720 lines?

I'm asking basically because if for some reason I need to work on a project where I want to keep as much res as possible but cannot afford to pay for, say, Digibeta capable editing time, I wanted to know if it was possible to transfer the raw footage to MiniDV so I can edit it on my own editing equipment while still retaining much of the horizontal resulition (even if it does mean introducing MiniDV compression)?
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Old February 23rd, 2004, 01:35 PM   #2
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Simon,

Camera resolution ratings are not calculated across the screen, like you said. It is calculated on a horizontal line the same length as the height of the picture. On a 4:3 aspect ratio picture, divide by 4 and multiply by 3.
For instance, the DV NTSC standard format is 720 x 480 pixel.
The ideal DV camcorder would be rated as 540 vertical lines of resolution on a 4:3 picture, even if it will show all 720 lines across the screen (720 /4 x 3 = 540).
Most DV and D8 camcorders reach a horizontal resolution rating between 400 and 520 lines, while VHS recordings cannot surpass 280.
Some Professional cameras heads like Digital Betacam can resolve up to 800 hor. lines, which will be converted to a max of 540 when dubbed to a DV format.
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Old February 23rd, 2004, 02:22 PM   #3
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Simon,
You might also find Adam Wilt's DV FAQ helpful in deciding what format to shoot in.
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Old February 23rd, 2004, 03:15 PM   #4
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Norm,

that isn't right I'm afraid.

Video resolution is measured in "horizontal lines" - best thought of as the maximum number of alternating black and white vertical lines (honest!) that can be displayed and resolved in the full width of a scan line. An unusual phrase to use, but that's how it is.

In analogue days this all made sense. There was no such thing as a digital pixel, and all signal levels wandered up and down in a continuous way. So the resolution obviously varied continuously.

With digital video it seems a bit confusing - after all there are 720 pixels from left to right aren't there? So surely it's always 720 horizontal lines? Well, that would seem to be the case. But if you calculate the total bandwidth required to carry 720 horizontal lines of resolution of a standard definition digital video signal, it exceeds the bandwidth available on a miniDV tape - there just isn't enough data space on the tape to carry it. In fact, there's only enough for about 530/720ths of the data, hence the assertion that a miniDV camera dn tape can only resolve 530 horizontal lines.

It's a maths thing. The 530 don't correspond exactly to pixel boundaries, so you won't see 530 crystal clear lines. It's just a measure of "roughly" how much "blurriness" and "noise" is unavoidable.

In short, you cannot take a miniDV shot of a 720 x 576 (720 x 480 NTSC) checkerboard and expect to make out every square.

Regards,

Julian
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Old February 23rd, 2004, 04:22 PM   #5
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Julian,
I'm afraid Norm is right...per the definition of video resolution. Please see the third paragraph in:

http://www.bealecorner.com/trv900/respat/#EIA1956

Also, if you scroll up from this page, there are references to other writeups on resolution.

You are also right. Although DV theoretically can resolve 540 lines, Adam Wilt reports that the bandwidth of Panasonic DVCPro tape at the 1/2 amplitude point is 460 lines over component connections.
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Old February 23rd, 2004, 05:32 PM   #6
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Quote:
With digital video it seems a bit confusing - after all there are 720 pixels from left to right aren't there? So surely it's always 720 horizontal lines? Well, that would seem to be the case.
You have to divide by the aspect ratio so that formats with different aspect ratios can be compared. Suppose you are comparing two a computer format that's 640X480 versus the same format turned sideways (480X640). They both have the same resolution. If you didn't divide by the aspect ratio, then the first format would have 640 lines and the second 480 lines. But that doesn't make sense, since both are exactly as sharp.

DV turned sideways versus normal DV would work like that if DV was using square pixels, but DV pixels are rectangular. But anyways, you divide the measured lines by the aspect ratio so you can compare the results against other formats.


Quote:
But if you calculate the total bandwidth required to carry 720 horizontal lines of resolution of a standard definition digital video signal, it exceeds the bandwidth available on a miniDV tape - there just isn't enough data space on the tape to carry it. In fact, there's only enough for about 530/720ths of the data, hence the assertion that a miniDV camera dn tape can only resolve 530 horizontal lines.
No, the information is stored digitally on DV tape and all the information is stored. In fact, you can even pack more information onto DV tape- that's how LP mode gets 50% run time at the exact same quality. That's not recommended though.

DV doesn't get 540 lines of resolution when you look at the whole signal chain though. You lose resolution at the CCD because of the Kell factor, and lose resolution when going from digital --> analog.

Adam Wilt's DV FAQ has lots of information on this (http://www.adamwilt.com/DV-FAQ-tech.html#DVformats). I gather from his site that DV and digibeta have the exact same horizontal luma resolution, but not chroma resolution. Also, DV and digibeta cameras differ a lot in quality, so not all DV cameras are as good as digibeta. A lot of DV cameras deliver really sharp pictures though, close to the limit of the format. I don't think digibeta is much of a significant jump in terms of luma resolution, although it has twice the color resolution.

You can get more resolution by shooting on HD and maybe film (70mm, 35mm, 16mm, etc.).
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Old February 23rd, 2004, 09:42 PM   #7
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http://www.dvfreak.com/res.htm
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Old February 24th, 2004, 02:58 AM   #8
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I stand corrected

Oh, bother. That will teach me not to post after a long day...

Please regard this as a passing senior moment...:)

Julian
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