new in DV editing, need help !!

Discussion in 'Video Cameras' started by Dr. Jai Maharaj, Jul 17, 2003.

  1. hi all,
    i am new here. trying to edit personal videos.
    i have a miniDV cam 800,000 pixel. but when i get the video files into
    computer,
    it looks like the AVI file has less than 500,000 pixel. Am using firewire.

    any idea why?

    thank you.
     
    Dr. Jai Maharaj, Jul 17, 2003
    #1
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  2. Dr. Jai Maharaj

    Tony Morgan Guest

    It might help if we knew what video editor you are using.
     
    Tony Morgan, Jul 17, 2003
    #2
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  3. Dr. Jai Maharaj

    Tony Morgan Guest

    Ummm... Don't you have more than one bit per pixel, Loz?
     
    Tony Morgan, Jul 17, 2003
    #3
  4. Dr. Jai Maharaj

    loz Guest

    Is that me personally? As in "one bit short of a pixel" :)
    Or are you talking about the way CCDs are measured?
    e.g. does an "800k CCD" really mean an 800k image?
    Normally specs tend to talk in terms of resultant image size don't they, as in
    the still image saved would be 800k pixels (regardless of what the sensor size
    is)

    loz
     
    loz, Jul 17, 2003
    #4
  5. Dr. Jai Maharaj

    Tony Morgan Guest

    AFAIK (no doubt someone will correct me if I'm wrong) the CCD size has
    nothing to do with the filesize. The camcorder's signal processor simply
    converts whatever the CCD produces into 720x576 pixels to be piped down
    the firewire. Then of course each pixel comprises 16 bits, so ISTM your
    calculations are a little awry.
     
    Tony Morgan, Jul 17, 2003
    #5
  6. Dr. Jai Maharaj

    loz Guest

    DV standard is
    720 pixels per line
    625 lines for PAL
    Though cameras dont usually resolve that many lines.
    The resolution of DV is consistently referred to as 720x576pixels is it not?

    And talking pixels is quite relevant here as
    1. the OP asked about pixels
    2. camera manufacturers insist on using pixels as a measure - hence the OP's
    original reference to his 800k pixel camera

    Loz
     
    loz, Jul 18, 2003
    #6
  7. Dr. Jai Maharaj

    Neil Tungate Guest

    Those are "samples", not "pixels". And the vertical number is 576 for
    PAL standard signals. And the samples are not square.
     
    Neil Tungate, Jul 18, 2003
    #7
  8. Dr. Jai Maharaj

    loz Guest

    what is the difference between a sample and a pixel?

    You are saying the standard is 720x576 "samples"
    And I earlier said it was 720x576 "pixels".
    I know, that's what I said.
    625 lines for PAL is also correct, that is what is sampled to get the 576
    pixel/samples
    Nor are the pixels.

    Loz
     
    loz, Jul 18, 2003
    #8
  9. CCIR 601 the standard which all the common digital video formats follow
    is 720x576 in PAL. AIUI the margins of the 'old standard' picture are
    lost for ever. ie. not sampled.
     
    Malcolm Knight, Jul 18, 2003
    #9
  10. Dr. Jai Maharaj

    loz Guest

    OK, having read a bit further I know understand 625 line PAL actually has 576
    "active" lines. And that is what gets sampled..
    Apologies if me earlier comments were incorrect re scanning of all 625 lines to
    produce the 576 samples/pixels.

    Loz
     
    loz, Jul 18, 2003
    #10
  11. Ok, you can be the expert now; it's a long time since I read the book.
    :))
    That's why I took care to pose questions rather than be too dogmatic and
    possibly be mistaken for a Welshman . ;-)

    IIRC we used to speak of 768x625 lines so by old standards quite a large
    chunk gets chucked away before the 5:1 DV compression kicks in.
     
    Malcolm Knight, Jul 18, 2003
    #11
  12. Dr. Jai Maharaj

    Guest Guest

    576 lines

    But Tony was suggesting you get 720 x 576 pixels down the 1394, but
    you don't -you poke DV, which is DCT/quantised/Huffman encoded video.
    Think of it as a stream of JPEG images.
    Do the maths : Raw 4:1:1 video 720 x 576 x 1.5 x 25 = 15 Mbytes/second
    versus a little over 3Mbyte/second for DV - what happened to the other
    12Mbyte?.
    Don't confuse bytes in a file with pixels.

    PeterS
     
    Guest, Jul 18, 2003
    #12
  13. Dr. Jai Maharaj

    loz Guest

    I don't think he was - that was just the way you chose to interpret it.
    All TM ever said was "...CCD produces into 720x576 pixels to be piped down
    the firewire". He made no reference to how those pixels are pumped, he just said
    "to be".
    Which are 720x576 are they not?
    But each individual 720x576 frame can be reconstituted from the stream.
    You now seem to be confusing the issue by introducing compression methods.

    I wasn't. It is fair to assume that when someone says they have a 800k pixel
    camera they are talking about the no. of pixels on the CCD, or in the image from
    it - not a 800k file size.

    Loz
     
    loz, Jul 18, 2003
    #13
  14. Dr. Jai Maharaj

    Tony Morgan Guest

    In message <>, Spam

    Snipped...
    Audio ?

    Anyway, all this discussion seems to stem from me mis-reading the
    original question (and I must admit some of the responses), and for that
    I apologise.

    Insofar a not poking DV down the firewire AFAICS you must do, since that
    is the resolution of the resulting video (until you run it through a
    codec to get MPEG-1, MPEG-2 or whatever when you make your movies after
    editing). What makes me believe that this is so is that some video
    editors permit you to grab a frame (to produce a still) and the
    resulting still is 720x576 pixels.
     
    Tony Morgan, Jul 18, 2003
    #14
  15. Dr. Jai Maharaj

    Guest Guest

    Well....no, not really - 601 is a 270 Mbit/sec stream (4:2:2 at 13.5MHz) -
    there are actually something like 864 samples per PAL line.
    I think the CCIR spec only specifies something around 702 active samples per
    active line.
    However, don't compare 601 which is a simple digitised stream, with DV which
    is a compressed format - the data in the DV stream is actually in the
    frequency domain, not the spatial domain as it is in 601.
    It is (relatively) simple to produce an image directly from a 601 stream,
    not so DV stream which must pass through a decompressor.

    PeterS
    Remove my PANTS to reply
     
    Guest, Jul 18, 2003
    #15
  16. 13.5MHz) -

    If you check back only a few days you will find I've already covered
    that bit of the story.
     
    Malcolm Knight, Jul 18, 2003
    #16
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