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Why is Digital8 camcorder passthru output different than its digital tape output?

I've been using a Digital8 camcorder to do some video capture using DV format, this case capturing 8mm film, going in to the computer via Firewire. I'm running into a problem.

I find that when I output through the camcorder directly to the capture program without recording to tape first, I get an odd vertical banding artifact when the resulting avi file is rendered for tape output or DVD. The banding isn't extremely pronounced but it's there and enough to be distracting when viewing. I'm basing this on what I see on a tv monitor, i.e. outputting to the tv instead of to a VHS tape, or playing a test DVD made from the file on a tv. However, this doesn't occur when recording to tape first in the Digital8 format and then outputting that to the computer and then rendering..

This banding also occurs when playing analog tapes through the Dig8 camcorder (this camcorder is backwards compatible) to the computer.

It doesn't occur when going through composite cables and capturing as an mjpeg avi file instead of the DV format.

I thought it would be the same, but apparently there's some difference in the DV output from the camcorder when doing it on the fly as opposed to going from DV tape output.

Any ideas why this is happening, why it would be different and how it can fixed? Capturing on the fly in the DV format is preferable for various reasons. Time savings and the size of the resulting files among them.

Using WinXP Home, Sony TRV-240 Dig8 cam, Pinnacle Studio 9 as my capture program. (Also tried using AMCap, with no difference in the results)

Thanks for all input.

Reply to
Doc
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A second isn't enough, you really need to see a fair amount of the video and see it on a tv to see it and the webspace I have available via my internet provider isn't large enough hold several seconds of raw video. The lesser resolution of even higher quality Windows media or Realmedia files obscures it.

I did put together a site where you can see it a bit through stills if you've got a decent monitor. Don't be misled by the presence of black borders on some of them. Some of them had had a border applied and the ones that are mjpeg hadn't. Doesn't have any effect on the banding artifact.

formatting link

Since I've tracked down the fact that it's there when doing it "on the fly", but not if doing playback from a Dig8 tape, finding out what's different about the output would probably yield some answers.

Reply to
Doc

You probably have web space somewhere where you can copy files for others to download? A short downloadable test clip (say, a second's worth of original, unprocessed DV AVI material that displays the problem) would probably help in investigating the phenomenon.

--
znark
Reply to
Jukka Aho

...

Powerline mains hum would appear as horizontal "banding". Furthermore, here in NTSC-land, the hum bars move slowly up the frame, taking ~10 seconds to make it through the whole frame. (This is because of the 59.94 field rate vs. our 60 Hz power freq.)

"Doc" said he was seeing "vertical" bands. Or perhaps he should clarify so we are all on the same page. Vertical bands is not a very common video artifact. I've never seen such a thing. Of course, a picture is worth a thousand Usenet postings and followups.

Reply to
Richard Crowley

Right. I remember both from back in the earliest video equipment I worked with (the last days of firebottles). But I've never seen anything like either of those in any solid state equipment (and certainly not in digital).

I'm guessing he means horizontal bands moving vertically.

Reply to
Richard Crowley

Personally, I'd be much more worried about the drastic color difference and not so concerned about these edges!

Guess: The passthru is going through an analog stage, probably to show OSD information. and you're seeing ringing on high-frequency components (vertical edges). The tape output does not go through the OSD stage.

Reply to
larwe

You have been through here before with this same "problem" and these same pictures. I'd guess that you may not get any better answer in this round.

When I crank my imagination up to 11, I think I can see your "vertical lines". At best they are what I would call a "3rd order effect". There are certainly much more deserving parts of the video that could use your attention.

Reply to
Richard Crowley

It seems to me you have a 60Hz hum when connecting to the computer. Try to run the camcorder only on batteries and use the same power strip for all connected gear, especially the computer and VCR.

--
ciao Ban
Bordighera, Italy
Reply to
Ban

I read in sci.electronics.design that Richard Crowley wrote (in ) about 'Why is Digital8 camcorder passthru output different than its digital tape output?', on Sun, 11 Sep 2005:

Thin vertical lines used to be a sign of parasitic oscillation in the equipment, not necessarily in the video chain. Horizontal/line output tubes/valves used to suffer from Barkhausen oscillation, which produced quite a crop of vertical lines.

Broad brightens variations, more 'stripes' than 'lines' can be due to velocity modulation of the horizontal scan.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

Not really a big point of concern. Different lighting situations, different projector and the mjpeg capture allows you to adjust the color balance as you capture. I just made the mjpeg captures quickly to see if the banding artifact was there.

OSD?

Hmm. Why would it not go through this stage with the tape?

Reply to
Doc

Since I have new information - i.e. noticing the difference between passthough and tape output, and posting to additional forums, I figured it would be worth putting it out there again. Plus, there's always a chance of getting it in front of different eyes.

They're there. No imagination needed. Those vertical lines that I described on the webpage are them, though they're more obvious when you actually see the video on a tv. This is the best I can do with limited webspace bandwidth. I'm more concerned with getting rid of this artifact than focus or whatever issues at the moment.

Reply to
Doc

If by "he" you mean me, I mean vertical bands. It's as if the image were being viewed through many, many thin vertical strips of glass whose edges are *almost* invisible but not quite.

Reply to
Doc

On Screen Display.

Perhaps because the passthrough is assumed to be a quick preview thing and the tape output is for production. Note, I did say it was a guess. My camcorders both show different information on the LCD vs. the composite output, and different information again on the DV stream. The LCD shows battery information and a bunch of other stuff; time, position on tape, etc. The composite output only shows an icon indicating the current function (PLAY, REC, etc). The DV output doesn't have any superimposed info.

Reply to
larwe

Essentially the same on mine. You can include the info on the LCD display on the composite output if you want (not sure why anyone would) but not on the DV output.

However, not sure about the "passthrough simply a preview tool" thing. Going by the manual, it's supposed to work, but clearly there's *something* different about the 2 different types of DV output.

Reply to
Doc

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