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Fields per second vs. Frames per second

Discussion in 'Electronic Basics' started by Radium, Oct 21, 2006.

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  1. Jamie

    Jamie Guest

    i did, and it's correct.
    currently my clock is saying 10:25 PM
     
  2. Rich Grise

    Rich Grise Guest

    Only by virtue of the fact that a video frame is delivered half at a time.

    A film frame is exactly where they got the name for a video frame.

    They're at slightly different rates, typically film is 24 FPS, and US
    TV is 30 FPS, but other than that and the interlace, the defninition of
    what a "frame" _is_ is practically identical.

    You might be interested to know that 24FPS movie projectors actually
    project each frame twice, so you get an effective flicker rate of 48
    FPS.

    Cheers!
    Rich
     
  3. Well, to be exact, the two fields of video are not quite the same as
    the three frames (not two, as I recall it - but it probably varies from
    projector to projector) of a film.

    The two or three frames (or call it fields - why not?) of the film are
    identical to each other, since they are just the identical piece of
    film projected again. If there is any motion in the subject, the two
    fields of the video are different from each other, since they are taken
    at different times.

    I'm just repeating Jukka Aho's point here for emphasis.
     
  4. Jukka Aho

    Jukka Aho Guest

    No, in other respects, too. Didn't you read the text you quoted above?
    US TV is 60 * 1000/1001 fields per second. The picture will update 60 *
    1000/1001 (~59.94) times per second. If a moving object - say, a ball
    rolling across the screen from left to right - is shot with an NTSC
    video camera, its motion (location on the screen) updates 60 * 1000/1001
    (~59.94) times per second. (That is, if we're still talking about
    material that was shot with a regular tv/video camera running in
    interlaced mode.) The location of the rolling ball differs from field to
    field, not only from frame to frame.
    It's not. Fields are shot at different times. When two adjacent fields
    are paired and combined into a single video frame, the end result will
    contain material from two different instants of time. A film frame only
    contains material from a single instant of time. (This is the reason why
    motion recorded with a video camera looks a lot smoother than motion
    shot on 24 fps film. Video _is_ smoother, by a factor of (about) 2.5.)
    It was interesting when I first heard about it. But that was a long time
    ago. :)
     
  5. Eeyore

    Eeyore Guest

    What does it matter to you ?

    You'll just misunderstand it because you're so damn stupid.

    Graham
     

  6. As usual, the greaseball is wrong. A TV projector in a film chain has
    a special shutter that runs the 24 FPS film to match the 30 FPS video
    rate by showing every 4th frame twice:


    Frames:

    Video Film

    01 01
    02 02
    03 03
    04 04
    05 04

    06 05
    07 06
    08 07
    09 08
    10 09

    11 09
    12 10
    13 11
    14 12
    15 12

    16 13
    17 14
    18 15
    19 16
    20 16

    21 17
    22 18
    23 19
    24 20
    25 20

    26 21
    27 22
    28 23
    29 24
    30 24

    This was done on the RCA TP-66 film chain projectors used by TV
    stations for decades.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  7. John Fields

    John Fields Guest

     
  8. Bob Myers

    Bob Myers Guest

    [example deleted]
    Hate to have to disagree with you, Michael, but that's no longer the
    way it's done, the TP-66 method notwithstanding.

    In modern practice, 24 FPS film is actually run at ~23.97 FPS
    (to enable a match to the 59.94+ Hz "NTSC" field rate), and then
    converted to video using a method generally known as "3:2 pulldown,"
    in which frame films are alternately captured as either 3 or 2 video
    fields (i.e., one frame of film winds up as 1.5 frames of video, while
    the next winds up as 1.0 frames). An example: if we have four
    successive film frames, A, B, C, and D, the resulting pattern of
    video FIELDS (not frames) would then contain the following:

    A A A B B C C C D D ...

    and so forth. While this still introduces errors (motion artifacts)
    into the resulting video stream, the errors are in general more
    acceptable than those which resulted from the earlier frame-
    doubling process.

    The original point in all this, though, I believe has been missed.
    TV "frames" are in almost all cases almost a fiction from the standpoint
    of image content; we speak of them only because, with the 2:1 interlaced
    scanning format, it's the only way to justify talking about the effective
    vertical resolution of the system (at least for still images). The two
    fields, however, DO represent different sample points in time, and
    therefore cannot in reality be assembled to produce a complete
    frame of the resolution (or line count) that one would expect, if there
    is any motion in the scene. (Moving objects, of course, will appear
    in slightly different positions between the two fields.) This is one of
    the factors that reduces the effective as-delivered resolution of an
    interlaced system.

    Bob M.
     
  9. Perhaps that is why Mr Terrell used the past-tense "was"?
    OTOH, his "greaseball" remark raises his "plonkability"
    score on my end.
     
  10. Jukka Aho

    Jukka Aho Guest

    Michael A. Terrell wrote:

    [awkward display of personal animosity snipped]
    The OP's question was "PAL video system uses 50 fields per second and 25
    frames per second. Whats the difference between 'field' and 'frame'?" He
    did not further specify the source or acquisition method, much less
    describe any practical situation from where it could be derived that
    film was the likely source medium. Keeping that in mind (and observing
    that the question was posted to "rec.video.desktop" which mostly deals
    with home and hobbyist video shot with home and prosumer video cameras),
    a reasonable assumption is that we're talking about "video" in its
    purest and most original form: interlaced video shot with an interlacing
    video camera.

    My comments in this thread have been based on that basic assumption
    (interlaced video shot with an interlacing video camera), and I have
    also explicitly _restated_ that assumption in a couple of my posts,
    precisely because there are some other acquisition and post-processing
    methods that can deprive video of its natural, smooth 50 Hz or ~60 Hz
    temporal resolution, or underutilize that capability.

    (Followups set to "rec.video.desktop" once again.)
     
  11. Bob Myers

    Bob Myers Guest

    And I'm thinking at this point that we still haven't answered that
    particular question very well, so I'm going to take a stab at it.

    In the most general sense I can think of, the word "frame" refers
    to the smallest unit in a motion image stream (a clumsy phrase,
    perhaps, but I'm trying to cover both film and video usage
    here) which includes ALL of the information for a single,
    complete image (i.e., it contains all the color, luminance, etc.,
    information for one image at the full resolution of the system).
    Ideally, it represents one temporal sample - i.e., it is an image
    which is captured at one particular point in time, in a series of
    such images which together are used to give the illusion of
    motion when displayed. This last point is where the notion of
    a "frame" in video starts to break down, since clearly in a
    raster-scanned system the entire image is not captured at the
    same time. But we still use the term nonetheless.

    A "field," on the other hand, is some defined sub-part of a
    frame. In the most common usage of this term - interlaced
    video, which is what we're talking about here - two "fields"
    are produced, which are supposed to correspond to (or
    be capable of being combined into) one complete frame.
    Again, it's not quite that simple, since in interlaced video the
    two fields are generally produced as such, separately, by the
    camera or telecine, as opposed to actually being the result
    of separating the odd and even lines of an original complete
    frame. This isn't the only possible use of the term; for
    instance, in "field-sequential" color systems (as in the case
    of the original CBS color system approved by the FCC in
    the early 1950s), the full-color frame is separated not into
    odd- and even-line fields but rather into red, green, and blue
    fields. These, when shown in rapid succession, restore the
    appearance of a full-color image.
    Hope you don't mind my adding sci.electronics.basics back
    in, as many of us (myself included) are following the thread
    there.

    Bob M.
     

  12. Bob, since the video camera scans both fields from the same frame of
    film, there is no "Difference in Time". The TP 66 could also run the
    color scan rates, and did in most installations. The pair that I
    maintained and ran happened to be used at a B&W station, but I've seen
    them in use at color stations.


    As far as slight differences, the persistence of the human eye tends
    to average out the minor differences. Most people can't see a single
    frame that doesn't match the film content, yet I could see the single
    "Insert Commercial here" frames in the AFRTS 16 mm films we ran. No one
    at the station believed me, so they opened a case of films that had just
    arrived, and loaded one. I hit stop when I saw it, and a few frames from
    where the shutter stopped, they saw it. I did it on six reels before
    they believed me.


    You may not like the "Frame" concept, but I find "Progressive Scan"
    to be stupid. Progressive? they went back to the earliest video scan
    method, and have the nerve to call it "Progressive"?


    The NTSC developers were not concerned about minor differences
    between fields, and unless a scene has a lot of motion, there may be no
    difference other than the offset spacing. Some talking head is on the
    screen, with nothing but their lips moving, and an occasional blink. Who
    cares about minor timing errors you can't see?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     

  13. I am tired of all his rants and preaching alchol and nicotine
    addiction and pushing a religious cult. I have 18 different screen names
    of his kill filtered, and still have to add new ones a couple times a
    year.

    If you want to "Plonk" me, go ahead.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  14. Jukka Aho

    Jukka Aho Guest

    That was a fairly good explanation, assuming the OP didn't know what a
    "frame" was in the first place. :)
    Originally - with tube cameras - none of the image was captured at the
    same time. Instead, it was a continuous process where the tube camera
    scanned the scene line by line, sweeping across the length of each
    scanline in lock-step with the tv sets painting the same picture on
    screen at homes. Essentially, each point in the picture was captured at
    a different time. There is a good illustration of this near the bottom
    of this page, below the ominous-sounding heading "It's Not Even That
    Simple":

    <http://lurkertech.com/lg/fields/fields.html#reality>

    Telecine processes and modern CCD-based video cameras of course do not
    produce images this way, but it is still useful to keep in mind that
    video cameras originally did - as late as in the 1980s. The original
    reality of "video" - and its "temporal dimension", so to speak - was
    fundamentally different from that of any frame-based system.

    Over the time, video has _become_ more like film, though - first by
    ditching the "scanning" cameras in favor of CCD-based ones, and now by
    introducing "progressive-scan" [1] HD formats, where video frames really
    _are_ frames, in the film sense.
    I don't mind if that's OK with the rest of the people in s.e.b. I just
    thought this subject might be a bit too off-topic there, and better
    suited for r.v.d only.

    _____

    [1] "Progressive scan" is becoming more and more of a misnomer in
    itself. These days, usually neither the camera producing the images -
    and, increasingly, not even the display device - "scans" any longer.
     
  15. Jukka Aho

    Jukka Aho Guest

    The "greaseball" remark was (seemingly) posted in reference to me in
    your post <Given the context in
    which that was remark was uttered, it's quite hard to interpret it in
    any other way.

    From the sound of the segment quoted above, it however now appears that
    you have me confused with the OP, who has displayed some trollish
    behavior in some of the other recent threads, and whom you specifically
    claimed to be a troll earlier in this thread (with much of the same kind
    of accusations about his earlier behavior.) We actually agreed on his
    trollishness, if you can still remember.

    I have never used anything but my own name on Usenet. You can check out
    my posting history from the Google Groups Usenet archives:

    <http://groups.google.com/groups/profile?enc_user=D3PrTBAAAA
    CQBxjOrkrNYwvJW2bfk89k>

    I have also no recollection of ever discussing alcohol, religious cults,
    or smoking on Usenet at any great length, other than what could be made
    in passing reference during a normal discussion. (I'm not much of a
    drinker, I don't smoke, and if anything, I would preach against
    religious cults rather than for them.)

    (I hope the above-mentioned URL is not temporary, but in case it is,
    look up any message by me from the Google Groups archives and click on
    the "view profile" link.)
     
  16. However, the "greaseball" remark was in a direct reply to my post in
    this part of the thread, so I assumed he meant me. Maybe he meant you,
    maybe he meant Radium, I don't know. Also consider that the post to
    which I replied was from someone name Rich Grise; maybe Terrell thinks
    his name is pronounced like 'grease'.

    If he meant me, it is in truth the most complimentary remark I've
    received today; also the *only* remark I've received today :)

    As for rest of your remarks below, it happens that I am in complete
    compliance & agreement (except for the URL, of course).

    It also happens that my remarks about movie projector shutters were in
    the context of projecting for view, not in the context of film chains
    for converting to video.
     
  17. :)
     
  18. Malleum mortuorum.
     
  19. Jukka Aho

    Jukka Aho Guest

    Hmm, yes, I can see now how there are other possible ways to interpret
    it. But, my name was mentioned in the quoted segment just above that
    comment, and the comment seemed to be in some sort of disagreement with
    what I had said. Or what you said I had said, and seemed to agree with,
    if you know what I mean. (This is the sort of confusion we get when
    people quote entire messages without trimming their quotes to the
    point.)
    Perhaps he meant himself. There are certain archetypical categories of
    people who are said to refer to themselves in third person, and
    self-hate is not a too uncommon disorder. It could be taken as some sort
    of self-irony as well. :)
     

  20. It wasn't amied at you, but the person you replied to. (grice) He is
    kill filed under 18 aliases, and keeps adding new ones.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
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