Re: 1080p vs 1080i
- From: "Matthew Vaughan" <matt-no-spam-109@xxxxxxxxxxxxxxxxxx>
- Date: Sun, 7 Oct 2007 14:39:55 -0700
<bingcheng01@xxxxxxxxx> wrote in message
news:1191612222.838580.290100@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Is it correct to say that both have the same spatial resolutions, but
each pixel in the picture is refreshed at a different rate b/w the two
formats?
Yes and no. First, for a still source image, yes, they should have the same
spatial resolution. But once the image is moving, the interlace degrades the
1080i image. It basically becomes a choice between annoying interlace
artifacts (comb patterns, etc.), or reducing the resolution by half (or some
combination thereof, with the persistent presence of filtering meaning that
even static scenes generally won't be as sharp in 1080i). Given that most of
the time only parts of the image are moving and that our eyes don't always
track moving objects that clearly anyway, 1080i ends up much better than
half as good as 1080p most of the time, but it's still not as good.
As for refresh rate, they're both 60Hz, so they can both reflect fast
changes well. It's just that the interlaced signal has those artifacts
(and/or reduced resolution).
In theory, the higher the update rate the better (this is not hard to
understand). But there has to be a threshold, due to physiology of
human vision, beyond which point it doesn't matter anymore.
Agreed. Though I suspect that figure is probably closer to the 60-120Hz
range than to 30Hz. (It certainly is when it comes to detecting flicker.)
Is 30Hz not enough to "fool" human eyes?
Generally, it's plenty fast enough to fool us into perceiving relatively
smooth motion, rather than a series of still images. (Even 15-25 fps is
often sufficient for that.) But that doesn't mean there is no improvement to
be had by going faster. It does depend on the source material, though - not
only that it does no good unless the source is faster also, but also that
fast motion (a wildly panning camera, etc.) will show the differences far
better than most average TV or movie material, which is relatively static or
at least doesn't usually move TOO fast if they want the viewer to be able to
follow it. (This should not be surprising, since it's almost all filmed at
either 24fps or 60Hz interlaced, and minimizing fast movement is desirable
for either situation, though for different reasons. Thus, cinematographers
are very aware of the framerate limitations of their medium, and plan their
shots accordingly.)
As for the possible advantages of a 1080p display, it's obvious that it
would be better for displaying any 1080 material than a 720p (or therabouts)
display, due to superior resolution. And that it would be superior to a
1080i display on any 1080p source material (at least on 1080p60, which
hardly exists, though probably a bit better on 1080p 24 as well). But it can
also improve the appearance of 1080i signals if good deinterlacing is used,
and can also fully show 720p signals with good upscaling in a way that a
1080i display can't. (At some point, a 1080i display essentially has to
throw away half the lines of a 720p signal, whether before or after
upscaling.)
.
- References:
- 1080p vs 1080i
- From: bingcheng01
- 1080p vs 1080i
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