[opendtv] Re: Why Europe should choose 720P for HDTV
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 13 Dec 2004 20:48:53 -0500
Craig Birkmaier wrote:
...
> For ANY given raster, the images will be sharper from a progressive
> scan camera versus an interlaced camera. Where we get into trouble is
> trying to equate different formats with similar pixel clocks, such as
> 720@60P versus 1080@60i.
>
> Clearly, the 1080 line format has more spatial resolution along each
> line, but the vertical resolution is subjective. We.ve been through
> all of the arguments before; the general consensus is that an
> interlace factor of 0.60 should be applied, bringing down the 1080 to
> 648, which is below the vertical resolution of 720P, but above 540,
> which is what is being sampled each field. This does indicate that
> the human visual system is integrating information between fields to
> provide the perception of improved vertical resolution. At least
> until an artefact comes along to spoil the illusion.
>
Craig -
I think with proper deinterlacing maybe you could get slightly better
than .6.
But let's use your numbers. Say, instead of 1920x1080i we forget about
the silly "interlaced square pixels" and instead used something like
1440x1280i, still viewed in a 16:9 resolution. This has only 1,843,200
pixels / frame or 921,600 pixels every 1/60 of a second. This is less
than 1080i and would be sending exactly the same number of visible
pixels per second as normal 720p. And at a slightly lower horizontal
scan rate.
But the 1280 interlaced lines might, by your number, produce the
equivalent effective resolution of about a 1280 * .6 vertical resolution
of about 768 vertical lines. So, forgetting for the moment how badly
MPEG-2 might compress 4:2:0 interlaced chroma, we might get an effective
1440x768 resolution for the cost of 1280x720.
> Bottom line. There is no reasonable justification for the continued
> used of spatio/temporal undersampling for digital television.
However I don't think interlace is the culprit here. It is the
obsession with square pixels that made 1080i so lopsided and thus
slightly short on effective vertical resolution. And extra horizontal
resolution that we rarely take advantage of.
The Australians might have made a better deal of it with their 1440x1080i.
- Tom
>
> Regards
> Craig
>
>
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