Television - how many Visible scan lines ??

Discussion in 'Amateur Video Production' started by ken, Jul 20, 2003.

  1. ken

    ken Guest

    I have seen so many numbers posted for this.

    The following article:

    http://data.uta.edu/~telemm/slides/pdf/M1/M1L3.pdf

    Says the followoing:

    There are 525 horizontal scan lines, for 262.5 lines per field. But
    each field requies 20 lines for "control info" at the beginning" I
    have never ever seen anything about "control info". I wondered if he
    means flyback, but the flyback lines occur at the end of each field,
    and there are only 14.5 flyback lines per field.

    Anyway - "assuming" he is right - the control info lines brings the
    number of "visible lines" down to 485 (525-20-20) - so the vertical
    resolution is 485. I am OK with this, since I have seen the number
    "480 and 486" quite a few times. Close enough.

    Question 1) there are also 15 lines use for flyback (moving the beam
    from the bottom to the top) at the end of each field !! This reduces
    the number of "visible lines" down to 455.

    Question 2 ) the same article says that you have a "maximum" of 485
    lines, but that "Ordinary TV" has 320 lines - where in the world
    does this come from ?? Even if he is talking VHS, I have always heard
    that VHS has 240 lines .

    Question 3) what about TV cropping? Doesn't this further reduce the
    number of visible lines ?

    This is so frustrating. I have spent 3 days reading on the web, and
    have encountered so many conflicting numbers. Don't even get me
    started on the DV 720x480 standard, when sent to television - that's
    for another time, but it is equally messed up as far as the many
    different numbers quoted.

    Lastly - I can't find a hompage for NTSC. FCC's site does not list
    these numbers, or at least I can't find them there.
     
    ken, Jul 20, 2003
    #1
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  2. ken

    Max Volume Guest

    That's because it's a standard, not a company, dumbass.
     
    Max Volume, Jul 20, 2003
    #2
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  3. ken

    ken Guest

    It's a standards committee - have you never seen a standards
    committeee website?
     
    ken, Jul 20, 2003
    #3
  4. ken

    chuck reti Guest

    Mr. "Volume"s helpful reply notwithstanding, hitting your friend Google
    with "NTSC" yields up the usual thousands of results, most of which
    contain useful information and tutorials that will explain the
    differences between scan lines, resolution, vertical sync interval, and
    lots of other things about How Television Works.
    NTSC stands for National Television System Committee,
    which devised the NTSC television broadcast system in the early fifties.
    So no, it's not a company, nor is it just a single "standard" it's the
    engineering group that a suite of standards and practices for analog TV
    transmission were named after.
     
    chuck reti, Jul 20, 2003
    #4
  5. SMPTE is an *ongoing* professional group.
    SOCIETY of Motion Picture and Television Engineers.

    NTSC was a *temporary* committee.
    National Television Standards COMMITTEE.
     
    Richard Crowley, Jul 20, 2003
    #5
  6. That doesn't mean that it can't have a web site though. In this case it
    doesn't make sense because NTSC was defined well before the web, but by
    Max's thinking there's no need for me to have a web site because I'm not a
    company. And no need for NATO to have a web site, or governments, or
    universities, or charities or, as above, SMPTE because none of those are
    companies.

    Gareth
     
    Gareth Church, Jul 20, 2003
    #6
  7. ken

    Mike Kujbida Guest


    Grow up Max. The first hit on a Google search showed
    http://www.ntsc-tv.com/
    BTW, it's National Television SYSTEM Committee.

    Mike
     
    Mike Kujbida, Jul 20, 2003
    #7
  8. ken

    Mike Kujbida Guest


    At least I took the time to do a search and provide some information
    relevant to the question instead of spouting "That's because it's a
    standard, not a company, dumbass".

    Mike.
     
    Mike Kujbida, Jul 20, 2003
    #8
  9. ken

    Max Volume Guest

    And for that you get a gold star and a smiley stamp. That was just me
    making fun of yet another clueless poster, but if you'd prefer to waste
    your time scouring the web looking for evidence that I'm wrong about
    something, that's your right I suppose.
     
    Max Volume, Jul 20, 2003
    #9
  10. ken

    chuck reti Guest

    Geez, man, get back on your meds.
    No wonder you've number one on the killfile list.
     
    chuck reti, Jul 21, 2003
    #10
  11. ken

    Mike Kujbida Guest


    You've got it wrong Chuck. No one takes him seriously so the guy's good for
    a laugh :)
    BTW, I hope to make it to at least one SMPTE meeting this year. Maybe I'll
    talk Rudy into coming along. We Canuks haven't been doing too good lately,
    have we?

    Mike Kujbida
     
    Mike Kujbida, Jul 21, 2003
    #11
  12. ken

    chuck reti Guest

    Yeah, I know, but it 's fun to tickle the trolls and see if they can
    ever post a reply without the word "****" or its derivatives in it.
    Hope to see you again at an upcoming SMPTE meeting. That's SMPTE, the
    Society of Motion Picture and Television Engineers. We have a website.
     
    chuck reti, Jul 22, 2003
    #12
  13. ken

    Nogami Guest

    That should be each "frame", not each field. There's certainly not 40
    lines off of the top of the screen. Typically the video information
    starts around line 22. Close caption information is on line 21.
    That actually combines with the 21 lines of the top to bring the
    number of visible scanlines down to slightly over 480. 480 is used in
    DV as none of the extra info is necessary. Some pro editing systems
    use 486 so they can also include captioning info in the outputs.
    The author has mixed up talking about vertical and horizontal
    resolution. Vertical resolution (525) is fixed, however horizontal
    resolution depends on the capabilities of the camera, recorder, and
    playback device utilized.

    Think about looking at a white picket fence with gaps between the
    white pickets. They're saying that on a VHS tape, you could identify
    120 individual "white pickets". On a higher quality playback, from an
    laserdisc for instance, you might be able to get 170 pickets. Since
    we use 720x480 resolution in DV, the most you could ever possibly see
    (not accounting for overscan) would be 360 pickets.
    Yes, that's overscan. On a 720x480 image, figure the outside 10-15%
    won't be visible on an average TV. It will be visible if played back
    on a computer screen though (DVDs for example).

    N.
     
    Nogami, Jul 24, 2003
    #13
  14. ken

    FLY135 Guest

    No wonder he is mixed up with this perpetuation of incorrect terminology.
    There are 525 scan lines of which ~480 have image information. This is not
    the same as vertical resolution, which is measured with a resolution chart.
     
    FLY135, Jul 24, 2003
    #14
  15. ken

    Mike Kujbida Guest

    chart.


    This is getting absurd. Let's try this explanation from the Grass Valley
    Dictionary of Technical Terms.

    "Horizontal Resolution:
    Chrominance and luminance resolution (detail) expressed horizontally across
    a picture tube. This is usually expressed as a number of black to white
    transitions or lines that can be differentiated. Limited by the bandwidth of
    the video signal or equipment."


    Or this one from http://www.videotek.com/app25.htm

    "First, Horizontal resolution is read by viewing wedges placed in the
    Vertical direction, and conversely, Vertical resolution is read by viewing
    wedges placed in the Horizontal direction. Imagine scanning from left to
    right on a single line, then the black to white to black transitions will be
    most obvious on lines which are perpendicular to the plane of the scan.
    Second, all of the wedges on the RETMA chart are identical and the numbers
    correspond to the number of lines, black and white, which can be drawn in
    the height of the chart. Since the chart is not square, the wedges presented
    in the vertical direction are not numbered for direct reading."

    Just to clarify things, there's a picture of this chart at
    http://www.halecolorcharts.com/resolutn.htm

    BTW, both of these companies have been involved in the TV broadcast industry
    for several years and know what they're talking about.
    Does this make it any clearer - or just further confuse things?


    Mike
     
    Mike Kujbida, Jul 24, 2003
    #15
  16. ken

    Mike Kujbida Guest


    Nope. It was your reply to Nogami's post that said "There are 525 scan
    lines of which ~480 have image information. This is not the same as
    vertical resolution, which is measured with a resolution chart."
    It's generally accepted that the number of active scan lines = vertical
    resolution.

    I'll go back to the Grass Valley dictionary which says
    "Vertical Resolution: Chrominance and luminance detail expressed vertically
    in the picture tube. Limited by the number of scan lines."

    I'm not saying that you're not correct (and you are), only that, in an
    attempt to educate some folks on this NG, we may be further confusing them.

    IMO, part of the problem lies with the manufacturers who very rarely quote
    vertical resolution numbers, only horizontal. Reminds me of the old days
    when audio companies quoted IPP (Instantaneous Peak Power) instead of RMS.
    Amazing how a 200 W. IPP amp became a 10 W. RMS amp :)

    It also lies with the creators of web sites who, for whatever reason,
    neglect to back up their statements, assuming that the average reader is not
    a televison engineer and therefore not capable of understanding the theory
    behind all of this.

    video.


    As I said above, are we further confusing things by attempting to simplify,
    as you've noted, a very confusing issue? Or should we state the absolute
    facts, hopefully with accurate links,
    to further the knowledge of those who are interested?

    Mike
     
    Mike Kujbida, Jul 24, 2003
    #16
  17. ken

    Mike Kujbida Guest


    You are 100% correct on the terminology confusion. My apologies for
    refuting your statement. Over the course of this thread, I've been
    frustrated at attempting to correct misleading errors and unfortunately
    lumped you in with al the other mistaken posters. Based on your previous
    postings, I should've known better. Thanks very much for your help on this
    issue. Much appreciated.

    Mike
     
    Mike Kujbida, Jul 24, 2003
    #17
  18. ken

    RGBaker Guest

    Would that it were so.
    I think it may be necessary to consider adding the word 'measured' to your
    definition of resolution. The concept of 'resolution' is elastic, in that
    photographic (and print) standards use a different and incompatible method
    of counting resolution; now that video & computers are embracing the term
    surely clarity is more important than historical usage. A photographic
    resolution chart shot with a video camera gives useless results if it is the
    common kind with markings to help you 'count' the lines.

    I'm reminded that I fume every time I hear the term 'ice hockey' -- as if
    there is any other kind! hockey! 'nuff said! -- the fuming is entirely my
    own cultural history speaking, not the fault of the speaker.

    Cheers,
    GB
     
    RGBaker, Jul 24, 2003
    #18
  19. ken

    Mike Kujbida Guest


    Sure there is. Let's see. Roller hockey, sled hockey, field hockey, floor
    hockey, etc.

    Oh, you're talking hockey as it's played in the Great White North? Then you
    can't forget road hockey where the Great Ones got their start :)

    Mike
    (who grew up watching the original six on CBC in the good old days)
     
    Mike Kujbida, Jul 24, 2003
    #19
  20. ken

    David McCall Guest

    No, you don't use a resolution designed for print, or even the chart used
    in film work, but there e is a resolution chart specifically designed for
    measuring video systems. A very popular variant that goes back to at
    least the 50s, and perhaps earlier is the familiar chart with the Indian
    head in the middle.

    Fume all you want, but kids in the city play street hockey in the summer
    when ice is more difficult to find.

    David
     
    David McCall, Jul 24, 2003
    #20
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