On Sat, 21 Dec 2002 11:44:23 -0500, "John S. Dyson" wrote:
>"Neuman - Ruether" wrote in message
>news:3e0a935f.4549518@newsstand.cit.cornell.edu...

[...]
>> >So regardless of the format, video is recorded in, the vertical
>> >resolution is always fixed, eg. for NTSC:
>> >
>> >mini-DV: horizontal resolution: 480 lines, vertical resolution: 525
>> >lines
>> >thus it is 525x480

>> NTSC, etc. vertical resolution is fixed, but the horizontal
>> resolution is not for analogue signals (though it is for
>> DV) - but these figures represent the MAXIMUM possible
>> resolution, not what you will get in reality...).
[...]

>I'd respectfully like to make a correction:
>
>The VERTICAL resolution (for NTSC and PAL) is NOT fixed to that
>implied by the scanning structure, but is limited by it. The vertical resolution is
>usually significantly less than the '480' or '576'. Even for progressive
>formats, you really want to filter the vertical detail. Similar to
>the 720pixels (or 540TVL) of horizontal resolution limit for DV, the
>vertical resolution is limited to 480 (for NTSC.) In order to mitigate
>interlace flicker and aliasing, you usually filter the vertical detail
>further.
>
>For highly compressed DCT-type schemes, you can measure resolution
>to nearly the limits, but also note that this high resolution isn't a general
>case (but specific to regular and simple patterns.) If the patterns become
>complex, then there'll be distortion of the signal, with loss of detail, but
>it doesn't look much like the softness of a simple freq response limit.
>
>John

Thanks for the clarification. I did not mean to
imply that the vertical resolution was set at a
specific value, but was limited by a specific value,
unlike the horizontal resolution... (I should have
said, "[the] vertical resolution [limit] is fixed"...).