[opendtv] Re: Frames Per Second of 720P

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 22 Jul 2008 06:56:49 -0400

At 4:48 PM -0400 7/18/08, Manfredi, Albert E wrote:
John Shutt wrote:

 This is exactly why I don't understand the nomenclature that
 seemed to only come into fashion with the advent of HD, of
 calling 1920x1080 thirty frames per second interlaced as "i60"

Two points:

1. ATSC documentation always says i30.

2. So, am I to conclude that 50+ years ago, 525/60 meant 60 frames per
second?


You might conclude this, but you would be wrong.

Before NTSC color we did have a true 60 field per second TV system, which change to 59.94 when NTSC color was added.

I believe the TV world is finally ready to admit that interlace sucks, but the legacy will be with us for many years to come.

The real travesty here is that the nomenclature for interlaced formats suggests that there is far more vertical resolution than is actually present. With field based systems we Do get the advantage of the higher temporal update rate (60/59.94), but at half the vertical resolution. The interlace pundits will tell you that you get more than half; they will talk about Kell factors and interlace factors, and say that you get 60 to 70% of the effective vertical detail of a frame based system.

But you also get interlace artifacts, and difficulties with encoding the color difference signals using frame based codecs like MPEG-2 (- yes I know that there are MPEG-2 tools for encoding interlace, but they also suck.

In my book, the the correct nomenclature for an interlaced 1080 line format should be:

1920 x 540 @ 60/59.94i

Regards
Craig


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