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General HD (720 / 1080) Acquisition
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Old April 4th, 2010, 09:11 PM   #16
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In an NLE, when editing interlaced footage, it operates field by field. It's the frames that "do not exist for any practical purpose".
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Old April 4th, 2010, 09:55 PM   #17
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The difference I am talking about is the display rate as perceived by a viewer or in fact an NLE. This perceived DISPLAY rate for 60i is 60 fps. In other words the image changes every 1/60 of a second, 60 new images a second ( yes they are only half the frame but at the real frame rate of 60fps). A CRT displays at this rate so the 29.97DF was perceived by a viewer on a CRT as 60 fps. Someone new could be misinformed into thinking that 60i was 29.97 transmitted as fields, ie a progressive frame rate of 30p transmitted as interlaced taking two fields to transmit the first frame etc. rather than 60fps with only half the information and thus termed 29.97( two fields make a frame ). That is all I am talking about. I am not trying or want to change the facts. Just point out that when I watch my CRT, plasma or LCD I do not see a DISPLAY frame rate of 29.97 for anything. I see 60i on the CRT refreshed every 1/60sec and perceive a frame rate of 60fps, on the plasma I see a deinterlaced picture displayed at 60P ( not quite as smooth as the CRT), on the Sony 240hz LCD I see an interpolated picture at 240 fps( very smooth).

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Old April 5th, 2010, 03:28 AM   #18
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What happens at the display stage can be very different to what happens at the acquisition stage. A cinema projector's shutter acts very differently to a film camera shutter.

Psf is another variation.

Progressive segmented frame - Wikipedia, the free encyclopedia

Time Code uses frame rates, not field rates.

SMPTE time code - Wikipedia, the free encyclopedia

In editing one of the fields is dominant.

Field (video) - Wikipedia, the free encyclopedia
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Old April 5th, 2010, 08:30 AM   #19
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Yes that is the point I am trying to make as well as the difference between temporal motion and arithmetic calculation of frame rate.

Option 1: A camera shoots at 30 frames a second but records or transmits a field every 1/60 sec.
Temporal motion is 30 fps.

Option 2: A camera shoots 60 frames a second and records or transmits a field every 1/60 sec.
Temporal motion is 60 fps

Arithmetically both are 30fps.. 60fields = 30 frames. Also support the same standard timecode. But they will look very different on display. And on which display they are viewed. They will not look the same on all types of displays, close but not the same.

Option 1 is how 30P is embedded in a 60i data stream used by several consumer cameras and some commercials and feature films shot at 30fps on film exclusively for TV viewing.

Option 2 is the way most NTSC 60i cameras operate. A growing number of consumer cameras actually operate at 60fps progressive and record progressive or interlace as selected. An example is the new Panasonic TM700

The numbers should really be 29.97 and 59.94 but for this explanation 30 and 60 have been used.

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Old April 5th, 2010, 04:59 PM   #20
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Perhaps not how it would be done now, but it solved a problem then.
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Old April 5th, 2010, 05:27 PM   #21
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Quote:
Originally Posted by Brian Drysdale View Post
Perhaps not how it would be done now, but it solved a problem then.
Absolutely. Times were very different and the recording and transmission of video was on the edge of what was economically possible. Present equipment is very good, we unfortunately still live with the legacy of the past in so many ways.

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