Re: Currently-Available Highest-Quality Linear PCM Video?


"Radium" <glucegen1@xxxxxxxxxx> wrote in message
news:1161134728.241862.77120@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

What equation did you use to get the numbers 720, 480, and 576?


No equation; that's what the standard defines. The 720
is the number of active samples per line; if you divide the period
of one horizontal scan line up using a 13.5 MHz sampling rate,
you will get 858 samples per line (in the case of the standard
"NTSC" line rate, 15.73426 kHz). Of these, 720 are "active"
(contain information corresponding to the actual displayed
image). The 525/60 scan format also has about 484 lines per
frame of active video (i.e., what's left - 525 minus 484 lines -
is used in vertical blanking), and CCIR-601 decided to use a
standard format of 480 lines just to round it to a convenient
number. Similarly, there are about 576 active lines in the
625/50 scan formats.

I don't know
what you mean by bringing "linear-PCM" into a question of
sampling rates and image formats.

Bob M.

Linear PCM is uncompressed PCM. Thats what I am talking about. Sampling
rate must be at least twice the highest frequency in the signal. Due to
physical conditions, it is safe to makes the sample rate at least 2.5x
the highest frequency signal.

Which has absolutely nothing to do with how the data is
encoded, which is what "PCM" is all about - hence I have no
idea why you are bringing that term up in a question regarding
sampling rates. Note that the 13.5 MHz rate easily meets the
Nyquist requirement of being >2X the bandwidth (technically,
it's bandwidth, not "the highest frequency in the signal) of the
video (note that U.S.-standard video occupies roughly
5 MHz of a 6 MHz channel).

What is the pixel X pixel resolution -- or "format" if you wish -- of
today's first-class video signal? Surely it would have to be more than
720 X 576. My monitor is displaying a pixel X pixel -- or "screen area"
-- of 1280 X 1024 with 32-bit color. I am not sure of the frequencies
of my monitor.

Standard definition video - i.e., anything other than high-definition
TV, which has different standard formats - is never any better
than about 720 x 480 pixels/lines for the U.S. 525/60 standard
format, or 720 x 576 for the "European" 625/50 format. The
actual effective resolution, in the proper sense of that term (the
degree to which detail can actually be resolved in the displayed
image) is generally a good deal less than this. Yes, computer
formats contain considerably more pixels than anything SDTV is
capable of.

Standard HDTV formats are 1280 x 720 pixels and 1920 x 1080
pixels.

Also, is there supposed to be a special difference between the first
number and the second number [such as 1280 X 1024 or 720 X 576]?

The way it's normally stated in PC usage, the first number is the
number of pixels per line, while the second is the number of lines
per frame. Traditional TV practice has been just the opposite -
give the number of lines first, then the number of "pixels" - but
actually, until the advent of digital television there really wasn't any
such thing as "pixels" in the TV engineer's vocabulary.

Bob M.


.

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