Re: 1080i format question

[Rich Torpey <rich(at)nyrhino.com>]

Matt,
If your interest is really in avoiding confusion than please go with 
1080i  when you are referring to imagery that was captured as fields and 
1080psf when referring to material that was captured as frames  - that's 
really what the basic difference is. 1080psf is merely a way of moving 
those bits that make up the frames from point A to point B. That's 
really what we're talking about.
When Sony introduced 1080psf as this wonderful advance in video I had a 
rather animated discussion with Larry Thorpe at the ITS Tech retreat 
(where psf was announced) asking how this major advance was different 
from normal practice in Telecine when we transfer at the native frame 
rate (30fps for NTSC or 25 for PAL instead of a more typical 24fps film 
rate). If you understand that at 30fps we are taking a progressive image 
(film frame) and storing it in two pieces you'll realize that it's still 
a progressive frame - THERE IS NO TEMPORAL DISPLACEMENT BETWEEN FIELDS. 
That's the difference between i and psf - strictly dependent on image 
capture  - the tape transport is just that, a transport medium.
No - all HDCAM is not 1080i - the purpose of a Cinealta camera is to 
capture a frame when you're in psf mode, not two fields.
The purpose of 24psf was twofold - 1) Yes, Sony did get to leverage 
their existing 25 frame equipment with minor modifications and 2) it 
allowed us two work with "Universal Masters" that could easily be used 
in the 30 or 25 frame worlds similar to using 24fps film.
You may remember a similar product some years back with D-1 vtrs. Sony 
came up with an option of running 25 frame offspeed and working with a 
Deft TK3:2 box to insert 3:2 pulldown to make a 30frame dub. This saved 
many passes in Telecine when transferring features - standard practice 
was to do 4 passes - scan & pan and letter box in both NTSC & PAL. Now 
you make one master in letter box and one in scan & pan which cut your 
telecine time in half.

1080i and 1080psf are not tape formats - they're image formats. It all 
depends on how you capture the images. Once the images are captured then 
you're just moving bits.

Mathew Sherman wrote:

> Tony, that's what bugs me about using 1080i as a conventional way of
> referring to 59.94 interlaced fields. In fact when Sony invented HDCAM and
> the F500 it was basically a glorified D-Beta machine. At the time (and maybe
> still?) nobody could get a VTR to have enough bandwidth to store progressive
> 1920x1080 frames at 60fps which would be referred to as 1080P/60. So what
> Sony did was split the frame in half (odd and even lines) and record the
> first part on tape as field one and the second part as field two, hence
> "PsF" which means Progressive, Segmented Frames. Yes, it is interlaced on
> the tape so, I'm assuming, a lot of the same SD electronics and circuits
> could be used (not sure about that, just guessing). All HDCAM is 1080i, not
> 1080P even if you are working at 23.976 or 25. That's why its important to
> say PsF at the end AND to know that the format you are working in is 1080i
> and not 720P. So yes, 23.976PsF HDCAM is still 1080i and yes it is
> interlaced, technically, on the tape, yes. DOES THIS MATTER? You ask? Well,
> again, I like to be specific and avoid confusion so yes I think it matters
> very much. To use convention just makes the somewhat elaborate and confusing
> issue even more difficult. Try explaining all this to a non-technical
> presentation person in charge of purchasing and broadcasting shows!
>
> ps, when we eventually do get a 1080P tape format this will become even more
> important since you could really have 1080/59.94P and 1080/59.94i which
> would be half the temporal information and both still 1080x1920.
>
> Regards,
> Matt <stickler> Sherman.
>
>  


--
Richard Torpey
VP Engineering
Rhinoceros/MultiVideo Group
50 East 42 Street
New York, NY 10017
(212) 986-1577
(212) 986-3833 fax
(212) 692-4465 direct


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