What is "pixel rate"?

Discussion in 'Professional Video Production' started by GreenXenon, May 6, 2009.

  1. GreenXenon

    GreenXenon Guest


    What does the term "pixel rate" refer to?

    GreenXenon, May 6, 2009
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  2. GreenXenon

    Smarty Guest

    Here is a technical explanation / definition of pixel rate:


    Richard Crowley, if you should happen to be reading this............ I seem
    to recall a somewhat famous troll who lurks around here at least once before
    asking these types of technical questions and then endlessly revising and
    reposting variations on the same topic. The last appearance a year ago maybe
    dealt with some RF issue. Is this "GreenXenon" or am I confusing this
    current legitimate query / poster with another person?


    Smarty, May 6, 2009
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  3. GreenXenon

    Smarty Guest

    Sorta' looks like the same guy, formerly known as GreenXenon Radium. The
    last trolling issue was antialiasing and jaggies, with other time wasters
    also such as "What video specifications are measured in Hz?"

    Where do these creeps and douche bags come from?
    Smarty, May 6, 2009
  4. GreenXenon

    GreenXenon Guest

    That website states "The pixel rate is a function of the horizontal
    and vertical resolution multiplied by the screen refresh rate [60 Hz
    in USA and Canada]. The table shows typical pixel rates for various
    standards. "

    However, something is wrong with that 'table'. Notice on the VGA, the
    resolution is 640 X 480 but the pixel rate is 25 MHz. That is wrong.
    The table even admit that the pixel rate requires that H and V
    resolutions be multiplied by 60 to get the pixel rate.

    By their own words they are wrong, because 640 X 480 X 60 = 18,432,000
    Hz or 18.432 MHz.

    So the pixel rate for VGA should be 18.432 MHz, not 25 MHz!

    This is so immeasureably frustrating and confusing. If, for VGA, the H-
    res is 640, the V-res is 480, the refresh rate is 60 Hz, and the pixel
    rate = H-res X V-res X refresh, then just how can the pixel rate be 25

    WTF is going on

    Whoever made the table deserves to have a 12 lb steel book slammed on
    their heads for getting it wrong!

    I'm so upset!
    GreenXenon, May 6, 2009
  5. GreenXenon

    Smarty Guest


    Did you read the link I sent you? Did you specifically see the very explicit
    and very obvious caution:

    "A simple multiplication of the horizontal resolution by the vertical
    resolution by the screen refresh rate results in a pixel rate significantly
    lower than the actual pixel rate. This is because approximately 30 percent
    of the video signal is taken up by vertical and horizontal blanking
    intervals that are not part of the active displayed image."

    This accounts for the "immeasurably frustrating and confusing" mistake /
    oversight you made.

    Pixels are being transmitted __ONLY____ during a fraction of the time when
    blanking and retrace are not occurring. The pixels are thus sent at a higher
    transmission rate determined by the number of actual pixels transmitted in
    the shorter remaining period, roughly 70% of the total period for the
    example cited. If only pixels were being sent and there were no need to send
    blanking and retrace information, then the rate for sending pixels would
    indeed be slower, in your example 18.43 versus 25 MHz.

    Do you mind me asking you......... WTF is a 12 lb. steel book?

    Smarty, May 6, 2009
  6. Yes indeed. This infamous troll uses several aliases repeatedly
    including "Green Xenon" and "Radium" and likely several others.
    We can take some small comfort knowing that he/she/it pulls the
    same kind of trolling stunts on several other newsgroups.
    Richard Crowley, May 6, 2009
  7. GreenXenon

    GreenXenon Guest

    Something with which you smack jerks who purposely mislead you.
    GreenXenon, May 7, 2009
  8. GreenXenon

    GreenXenon Guest

    That is another question I have.

    In the old days of B&W films, what components of a video signal [in
    the film itself] would be considered "frequency"?

    I can think of two - temporal frequency [usually measured in Hz or
    cycles per second] and spatial frequency [usually measured in cycles
    per meter]. What else?

    Also if an image is high-pass filtered, it looks sharper, if low-pass
    filtered it looks dull. The type of frequency being altered here is
    called the "spatial frequency". Or so I guess.

    Stationary pictures do not have a temporal frequency component. Movies
    GreenXenon, May 7, 2009
  9. GreenXenon

    Smarty Guest

    A potentially useful item, no doubt. Please identify a URL with a source for
    purchasing these items.
    Smarty, May 7, 2009
  10. GreenXenon

    Smarty Guest

    We are making huge progress. You have both posed and then correctly answered
    your own question.
    Smarty, May 7, 2009
  11. GreenXenon

    Smarty Guest

    Thanks Richard. There was a familiar tone to Radium's original message which
    has a weird juxtaposition of ignorance and knowledge. My take is that the
    questions are being posed by someone who is reasonably astute yet prefers to
    play mind games.

    Perhaps an escapee from "Second Life" who has run out of Linden
    Smarty, May 7, 2009
  12. GreenXenon

    GreenXenon Guest

    What entities in a single stationary negative image of a B&W film are
    measured in Hz?

    What will the image look like if I change the frequencies of those
    entities to 0.1 Hz?
    GreenXenon, May 7, 2009
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