Invisible <voi### [at] devnull> wrote:
> Quadrupling the number of pixels doesn't necessarily mean that the 
> *compressed* signal takes more bandwidth.

  It depends on the video contents and the codec.

  If you take, let's say, a 640x480 video and quadruple its size to
1280x960 (using some interpolation filtering), you won't need significantly
more bitrate eg. on MPEG-4 to get the same picture quality. That's because
the larger version doesn't contain any more information than the smaller
one (any additional bitrate you might need comes mostly from other overhead
caused by the larger video size).

  However, if your *original* video is 1280x960, at full detail, then it
will contain significantly more information than the 640x480 version. Most
of this extra information will get mangled if you use the same bitrate as
you did with the smaller video (assuming the bitrate was pretty optimal for
it to begin with). You will need more bitrate to retain that extra
information as much as possible (although not four times as much, of course).

  This is so for MPEG-4. Digi-TV (at least here) uses MPEG-2 (the same as
DVDs use). I don't know how well that handles larger video resolutions
compared to smaller ones.

> Then again, since we replaced our old CRT with a shiny new LCD, suddenly 
> I notice that just about *everything* on TV has DCT artifacts all over 
> it. (I guess the CRT was too blurry to show this.) It's quite annoying.

  Most digital TV broadcasts use significantly lower bitrates than DVDs,
which is why most digital TV broadcasts have significantly more visible
artifacts.

-- 
                                                          - Warp

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