[Tig] hd "formats"

David L. Tosh dlt
Mon Nov 5 20:21:44 GMT 2001

At 02:39 PM 11/5/01 -0500, Greg Dildine <greg.dildine at finishedit.com> wrote:
>Can someone please clarify (again) the 59.94 vs 60, 29.97 vs 30, and 23.98 
>vs 24 rate "thing" again ...

The difference becomes important when you consider the environment of the 
shoot. For a purely "video" production and post environment, choosing the 
-0.01% variation of the basic frame rate guarantees no (fewer ;->) 
synchronization issues. You can mix HD 59.94 interlace, 29.97 progressive 
and 23.976 progressive with standard definition 59.94 interlace and double 
system audio recorded at 29.97. All capture rates are related, all post 
production rates are related and nothing is subjected to "pull down."

If you mix HD cameras in a traditional film world, you want to capture at 
the evenly rounded rates of 60.00 interlace, 30.00 progressive and/or 24.00 
progressive. This will match the 24.00 film camera rate and the double 
system audio recording at 30fps. It is less intrusive to a working film 
environment to match their pace than try to get the film camera to run at 
23.976... (Yes, it could be done, no I haven't seen it happen yet.)

Usually the biggest consideration for the choice of zero or -0.01% capture 
rate is if you want NTSC down conversion on the set. The down converters 
really "want" to produce real NTSC rates of 59.94 interlaced video that 
standard VTRs can record and to which standard color monitors can lock.

When you move to post production in a mixed "NTSC" environment, elements 
shot at 60/30/24 are simply slowed down (akin to pull down we speak of with 
audio rates) to produce a frame-per-frame post environment.

No temporal interpolation is happening-- the original frames (fields) are 
played without change, they are just played at a different rate.

>Back to my TECHNICAL question...
>Could the dp have recorded at 30Psf and what benefits or PROBLEMS 
>would/could result?  I'm assuming that they picked the 29.97Psf "rate" for 
>a temporal resolution close to film (30fps), and progressive to avoid 
>interlace artifacts and temporal differences, and avoided 60i (or 59.94i) 
>to also avoid other interlace and temporal differences, and avoided 24 
>(23.98) to avoid 3:2 (which our UK friends point out is not part of the 
>film-to-tape "aesthetic" anyway in their part of the world).

Yes, you can choose 29.97 progressive for the temporal capture look and 
still play it back into an interlaced 59.94 interlace environment-- we've 
been doing that for years with film transfers. Film frames are scanned 
progressively but carried in segmented form in NTSC and PAL.

And there is a whole different look between 30P and 24P images well beyond 
any discussion of 3:2 sequences.

David Tosh <dlt at earthlink.net>
Engineer, Complete Post Hollywood, CA USA

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