Does it help to lay colour bars on DV or DVCAM tape before shooting?greenspun.com : LUSENET : Shooting DV Films : One Thread
Does it help to lay control track (such as colour bars) over a miniDV or DVCAM tape before shooting? In umatic and betacam it improves and makes the picture more stable. Does it happen in DV also? I also want to know why I see pixel blocks in my DVCAM raw footage (it is occassional but it really spoils good footage sometimes).
Thanks a lot in advance and with best regards, Suman.
-- Suman Basnet (firstname.lastname@example.org), November 15, 1998
I'm not an expert in this, but I've always considered color bars useful for callibrating color and editing components, not for any impact on the actual raw footage quality.
Two things other things to consider... 1. The popular mini-DV cameras (Sony VX1000 and Cannon XL1) have the ability to produce color bars, although it is undocumented in the Sony. BUT, they are not true NTSC bars. I don't know how useful your post facilities will find them.
2. There is an argument for writing to your entire tape before shooting. If I am going to use the same mini dv tape with long breaks between shooting I will record the entire tape(s) over the nite before in black with no audio. The purpose is to lay down a continual time code on the tape. If you don't, the DV camera will start up at every significant shooting break (camera power down) with the time code reset at 0:00:00. If you intend to do batch capture off of your tapes--very useful in many NLE environments--not having a continual time code through the tape is a HUGE headache.
Incidently, you can also avoid this problem if you rewind slightly before shooting. You overwrite a bit of the last recording, but you'll pick up the time code where you left off. I'd just prefer to remove this extra bit of worry during shooting.
-- John P.S. Oh yeah, you definately should stick some true NTSC color bars on your final master after editing. Most reasonably good editing systems will let you do this.
-- John Windmueller (email@example.com), November 16, 1998.
I've been working with a Canon Xl1 trying to digitize its generated color bars into an Avid, going in component video and calibrating through the avid's vectrascope... bottom line is that the canon's color bars SUCK in terms of any kind of a useful reference. Trying to get the color spikes to come even close to where they're supposed to be is impossible- perhaps on a real analog waveform monitor this may be easier to do, but I doubt they would provide any useful reference for good looking video. In other words, any color bars you may record for reference is a waste of time since you'll be better off just using your own judgement of your footage. Compare the bars to a real SMPTE color bar pattern and you'll see the huge difference.
Hope that helps
-- memo salazar (firstname.lastname@example.org), July 27, 1999.
DV and DVCAM tapes by definition do not have, nor do they require, a control track. I've read many forum entries written by people who are wasting valuable time "striping" or "black-bursting" their DV tapes, for continuous timecode and what they think is control track, essentially turning their stock into what broadcast oldtimers commonly refer to as "crystals" or "crystal blacks." The digital revolution, for lack of a better term, makes this unnecessary. There's a reason why the oldtimers were doing it- A) in most broadcast formats (Betacam SP / SX / and I think Digibeta too) you can't insert edit over a section of tape that lacks control track. At best, the edit will play in the machine that made it, but you'll almost always end up with a surprise when you try to playback that tape in any other machine. B) The old stuff, and even new non- linear edit systems, at best like to, and at worst NEED to see continuous timecode. Here's what you do. Lay bars over the first 30 seconds to minute of your tape with a preset timecode that makes some kind of sense-- I start at 23:59:40, lay :20 of bars, and start my footage right at 00:00:00-- this is my own habit. Most broadcast facilities choose 00:59:xx with the real stuff starting at one hour. At any rate, after you've laid your bars, leave your TC generator on regen and voila! Continuous timecode. As for your pixelation, if it's anything worse than DV / DVCAM's tendency to stairstep contrasty horizontal lines, or any other compression anomaly, you're in trouble. If it's big blotchy digital cubes across your footage, like I suspect, then you've got a malfunction somewhere (clogged heads?) and should have it checked out. --John Griffin
-- John Griffin (email@example.com), April 12, 2002.