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Interlacing... confused again...

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dan smithInterlacing... confused again...
by on Jan 30, 2012 at 2:49:11 pm

I hate when of a morning my, what i belived to be, rock-solid understanding of a concept it destroyed! Please help me to understand interlacing (again…) I have read around the subject and think i understand, but you can't ask a book a question…

We occasionally use our old sony v1 camera that shoots 50i (we are in the uk) my boss tells me that 50i is the same as 25p. This i took for granted for the last year- I always thought that a 50i image could be effortlessly combined to make a progressive image as each set of fields makes a full frame… just select 'none' in the frame order tab on FCP and hey presto - de-interlacing by field combination. but to my horror i found today that the camera actually records each set of fields sequentially (i.e 1/50 sec apart) and therefore what i though was one progressive frames' worth of image in 50 fields is actually temporally different by 1 50th of a second. This has lead me to believe that i have been using final cut in error for quite a while - after we ingested 50i footage i set the field order to 'none', assuming that that means the footage will be treated as progressive. I think, by doing so, i've been de-interlacing the cheap and nasty way - by throwing away a whole set of fields. is this the case? if so, is there anyway to make my footage work with progressive footage on the same timeline? - should i de-interlace by interpolation?

I noticed that often when ingesting 5d rushes to prores hq final cut has given the clips field dominance - I really don't understand why that is - any ideas?

Thanks guys!


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Andrew RendellRe: Interlacing... confused again...
by on Jan 31, 2012 at 12:22:45 pm

You can't ask a book a question, but you can read the words!

I think that if you don't know that in an interlaced scan records a field 1, with it's lines numbered 1, 2, 3, 4, 5, etc, AND THEN records a field 2, with that's lines numbered 563, 564, 565, 566, etc, (that's for HD, the field 2 line numbers for PAL and NTSC are different ones), you really ought to learn some technical information ASAP.

[TBH, I've always thought that describing what everyone knew as field 1 and field 2 as "odd & even", "top & bottom" or anything else were simply examples of deliberate obfuscation designed to add a layer of unnecessary jargon that only confuses people.]

Start with this!!PDF-E.p...

and every time you see something that you don't understand, ask someone or get on the internet and find out.

[BTW you can have a picture that's taken all at the same time in an interlaced signal, i.e., both fields actually recorded by the camera at the same moment rather than a 50th of a second apart, but that's called Segmented rather than Interlaced to avoid confusion.]

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dan smithRe: Interlacing... confused again...
by on Feb 1, 2012 at 10:53:46 am

slightly harsh, but thanks anyway!

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Andrew RendellRe: Interlacing... confused again...
by on Feb 2, 2012 at 9:35:21 am

Sorry about the tone, just finished a fast turnaround (cut a 47min doc in 11 days). If I wasn't tired I'd have said basically the same thing but in a more gentle and encouraging manner ;-)

BTW, this one:

It's on 4OD for the next 4 weeks if anyone's interested. I think it stands up as pretty good even without considering the speed at which we cut it! (But then I'm biassed, ok.)

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