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Interlacing… confused again…
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!
dan
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3 Replies
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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
https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-5-200204-I!!PDF-E.pdfand 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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slightly harsh, but thanks anyway!
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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:
https://www.channel4.com/programmes/terror-at-sea-the-sinking-of-the-concordiaIt’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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