Re: Why interlaced HDTV?

On Mon, 22 Aug 2005 09:09:34 +0100, Kennedy McEwen
<rkm@xxxxxxxxxxxxxxxxxx> wrote:

>But it is infinitely easier to display interlaced video correctly, and
>without a frame store, on a progressive screen than it is to display
>progressive video correctly on an interlaced screed.

All current progressive screens are by their nature a frame store. By
displaying interlaced material you are effectively displaying two
fields shot at different times simultaneously. This has the effect of
degrading the apparent resolution of the system.

>In the former case, all that is necessary to do the job correctly is to
>store a line of video at a time, write that onto the line of pixels on
>the progressive screen and then blank off the pixels on the subsequent
>line. In the next field, simply blank the pixels on the first line
>(which were written on the previous field) and write the pixels in the
>next line (which were blanked on the previous field). This reproduces
>the interlace structure with the exact time latency and spatial
>structure of the original format.

This is not however how LCD and Plasma screens work and to try and
replicate this would create all the traditional TV flicker that these
screens are so good at eliminating while introducing other artifacts.

>You can't do that the other way round, if the display is interlaced by
>default, without destroying the latency between adjacent lines.

It's always a compromise. Even in todays broadcasting world I'd prefer
interlaced material to be deinterlaced by an expensive box at the
broadcaster than in a £ 5 or less chip in my TV. In future most new
productions will be natively progressive so the problem will be
eliminated. To take progressive material, interlace it and then
de-interlace it would of course be even more crazy.

Rgds
Jonathan



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Relevant Pages

  • Re: Why interlaced HDTV?
    ... A progressive display can be configured to display interlaced material perfectly correctly. ... That particular trade-off results in 50Hz flicker, but no worse than on a conventional interlaced CRT. ... However there is a third trade-off which maintains the flicker elimination of these screens. ... You can display interlaced images on a progressive screen correctly, and I suspect that the reason it isn't done has more to do with manufacturers agendas than a limitation of interlace per se. ...
    (uk.tech.digital-tv)
  • Re: HDV camcorder with 720p
    ... May I also suggest that you download some Sony HDV samples from the Internet ... Interlace is fixed by deinterlacing which in effect means that you try ... -If your main intended display equipment is interlaced (as for example ... limitations of shooting at low frame rates like 24P or even 30P. ...
    (rec.video.desktop)
  • Re: Why interlaced HDTV?
    ... >To display such a signal with the whole picture changing 50 times per second ... which is why interlace has been used by all broadcasters since the ... >Updating only one field's worth of the picture, or half the number of picture ... which is why there is a move to 1080p/720p 50 FRAME ...
    (uk.tech.digital-tv)
  • Re: 1080i or 720p
    ... display causes information to be lost forever. ... I'm talking about any content that has been converted for interlace display or captured with an interlaced camera. ... it was converted to or captured as interlaced and information that a progressive capture would have had is *not* recaptured by de-interlacing. ... A careful reading of that source shows nothing to support your theory that information lost during the capture of or conversion to interlaced format can be recovered by de-interlacers. ...
    (alt.tv.tech.hdtv)
  • Re: Upconverting question
    ... It is more of a concern how the interlace is performed and what ... The big advantage I see in all the new formats in DTV is alternatives to ... Then a 24 fps video stream could be upscanned to 48 fps or 72 fps ... need for the content source to dictate the actual display rate. ...
    (alt.tv.tech.hdtv)