Field Ordering

[E_Tedeschi]

Hello all,

I can't seem to find a defintive answer to this question:

Why does the field order for PAL video change from hardware to hardware, and considering these differences, why do they not cause issues when moving footage around between gear?

For example, PAL DV in FCP is ordered lower-field-first. Avid at 2:1, say, (and most other resolutions as far as I can tell) is ordered upper-field-first. This is of particular interest when doing FX work (eg After Effects). I always match the field order of the hardware I'm working on, and I have never had any issues.

As far as I can tell from my googling, though, PAL is broadcast upper-first, so what gives?

e.

[JWRL]

Historically PAL from the 2" quad days has been defined as upper field first. Avid in their implementation of PAL followed this practice. However when DVcam and miniDV came along they were defined as lower field dominant, so if you edit on an Avid using a DV codec it will also be lower field first.

For interchange purposes the field dominance doesn't matter at all on video. All that it affects is the position of pulldown in a telecine transfer and the field on which an edit will take place.

However if you get the field dominance wrong when doing anything to the video that requires reprocessing it can jump up and bite you. For instance, if you specify the wrong dominance for AE, Combustion, or any other video compositing package you can end up with the classic flickery motion effect. Similarly if you specify the wrong dominance for MPEG compression for DVD burning you can also achieve pretty disgusting results.

[E_Tedeschi]

Thanks, JWRL. I knew I could count on you!

I have posted a link to your reply on www.creativecalf.net, where I am a forum leader - I was discussing it with Mark Wesley:

http://creativecalf.creativecow.net/cgi-bin/new_read_post.cgi?univpostid=871450&forumid=2&postid=871450&pview=t

Thanks!

e.

[JWRL]

Thanks, E, and I hope it clarifies the issue at creative cow.

For what it's worth I have the field step function on my Avid mapped to shifted forward and back arrows on the keyboard. I can then easily single-field step through freshly imported off-site material and verify the field dominance. I can't remember if FCP offers a similar function, but there's probably something similar that you can do there as well.

[E_Tedeschi]

No worries. Mark was quite appreciative also.

I'm not sure if FCP has a field-step function... I shall investigate further.

Quicktime can usually reveal the field dominance in the clip's info tag even before importing into FCP. That's usually what I go off if I suspect that there's an interlacing issue.

e.