Shifting Fields hmmmmmm

i read a lot about shifting fields in this forun. in a recent thread someone mentioned that hd footage field dominance is upper first. in another thead i read that shifting fields in dv footage will better match hd (1080i).

so why would you want to shift fields?
how is the decision made?
if shifting my field dominance will make it a better match to 1080i why not shift it most of the time for quality reasons?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

hello i'm an orphan over heyer.

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

Field dominance isn't as arbitrary as you are making it. Its specific to different formats. I would try reading up on it first before posting, your questions are too broad and that's why no one is answering them.

Why don't you run some tests & get back to us with your findings

When life gives you dilemmas...make dilemmanade.

[so why would you want to shift fields? ]

One answer- when you reverse action.

Try it and monitor on a CRT-- you won't see it on your LCD.

- Loren
Today's FCP keytip:
Invoke the Audio Mixer with Option-6 !

Final Cut Studio 2 KeyGuide? Power Pack.
Now available at KeyGuide Central.
www.neotrondesign.com

when i do try it the only thing i really notice is that color seems stronger.

i am monitoring it FW ntsc thru a consumer camera on a cheap 2005 daewoo 19" tube tv.

would a more direct question help.

what does shifting fields do?

i know it has something to do with which lines are being seen. i kinda think that shifting to upper odd mean to look at every other horizontal line in the first number of the aspect ratio. such as in 720x480 there are i think 720 lines going horizontally so from my lack of knowledge i am thinking that when i see this aspect ratio and then say upper odd, i am telling fcp to look at every other line in the 720 first.

i am probably wrong but this is what i am trying to understand.

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

with interlaced video each frame is made up of 2 fields, each containing half of the picture information. those fields are recorded consecutively, and must be played back in the same order or the motion will stutter (think 2 steps forward, 1 step back ... in this case each "step" is a field)

if you are working with SD NTSC then there are 625 lines of resolution. with upper field first, the first field will contain all the odd lines of resolution, the second field will contain all the even lines of resolution. with lower field first then all the even lines are in the first field, all the odd in the second.

thats why its important to play back the fields in the right order ... if you put odd (upper) field first video into a even (lower) field first timeline then the image will stutter as the fields are played back in the wrong order (2 steps forward, 1 step back).

in order to compensate, we add the "shift fields" which pushes the image data on the even lines up (or down) one line onto the odd lines, and the odd lines onto the even, therefore shifting the fields so that they playback in the correct order

nice answer, andy.
Progressive mediums (eg, film) captures full frames, interlaced mediums (eg, tv) replaces the frames with fields, which playback twice per "frame count". PAL is 25 fps, resulting in 50 interlaced fields a second. A simple way to look at it is to divide your tv into horizontal lines, and number them 1 to 10. The odd ones being "odd/upper", since it starts higher than the even fields. Let's say you're upper field dominant (meaning that these odd lines start first). The 2nd field, would have been recorded half a frame later than the odd/upper lines. So when the field dominance is mixed up, eg, in our case, it plays the lower/even lines first then the upper/odd lines, reversing the order of playback every frame... The result is a stuttering of motion and scan lines become pretty clear.

THANKS BIGTIME

so would i be correct to think of the "stutter" as the same the same sorta/kinda stutter that one may see when doing a 9sec pan on a camera whos pan calls for 12sec. i know in that case the stutter is caused by missing frames causing a jumpy pan.

could i think that the field dominance stutter to be more like, it is playing back but its looking like it almost is skipping frames.

the scan lines i am thinking are kinda like what you see when blowing a video up to 200%.

so , how would i know if i need to shift the field?

i think that maybe you are more likely to shift fields when you are dealing with footage that came from multiple cams or sources. it would seem as thought if i use 2 dvx cams to film that the footage i obtain would be identical in fields. however if i used a jvc hd cam and say a dvx then i may have field issues.

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

J
dont think of the incorrect field order as being like anything else, think of it as being what it is!
the explanations above try to clearly describe the cause and effect of the "stutter"
cause: playing back fields in the wrong order
effect: the later motion plays back before the earlier motion in evey frame

you would use "shift fields" to fix such a stutter. that would be if, and only if, you were using source footage whose field order did not match the sequence codec's field order
if you put HDV (upper field first) in a DV timeline (lower field first) then you would need to apply the shift fields filter ... in fact FCP knows and understands this already and applies the shift fields filter for you, it just does it automatcally in the same way that it resizes the HDV footage to fit the DV frame size. the problem is that sometimes field order is interpretted incorretly, in this case FCP doesn't think the shift fields filter is needed, so you would have to apply it manually.

ok i think i got it.

as a fail safe is there anyway to ask fcp to adjust/check fields?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

> as a fail safe is there anyway to ask fcp to adjust/check fields?

FCP generally adds the filter automatically when a clip is imported that has the opposite field dominance. However, sometimes it does it wrong. You'll have to watch on an external monitor and see if the motion makes sense. I know I had to adjust a few Shift Fields filters manually when I imported HDCam clips into an Uncompressed 10-bit SD timeline once.


www.derekmok.com

derekmok Wrote:
-------------------------------------------------------
> > as a fail safe is there anyway to ask fcp to
> adjust/check fields?
>



Generally we call that "eyes".

Yeah, you can easily tell when the fields are shifted incorrectly. The motion is very obvious.