A primer on "resolution"

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  • woodman
    Junior Member
    • Sep 2002
    • 8

    A primer on "resolution"

    There's been so much confusion and misunderstanding about this aspect of HomeTheater, that I decided to post a primer on the subject to try and help those that are unsure about it, or even worse - are totally confused.

    To start with, those who've grown up with computers need to learn one very important fact. That "resolution" in a video display is not the same thing as it is when applied to computers. They are quite different because - in a computer monitor, as resolution is increased, objects on the screen get smaller. In a video display, this is not the case at all. This fact changes everything - especially the notion that the number of scanning lines is directly related to the "resolution" of the image. Simply not so. The number of scanning lines that make up the image DO define "vertical resolution" but that is not what's being discussed when the subject of "resolution" comes up.

    Let's start with some definitions of terms:

    Scanning lines
    ... the 'lines' that are "painted" by the electron beam(s) as they sweep across the screen, making up the image.

    Scanning formats
    ... the number of scan lines that makes up one "frame" of video, plus whether it's scanned "progressively" (p) or if it's "interlaced" (i).

    Interlaced scanning
    ... the scanning of a video image in which there are two "fields" scanned to produce each video "frame". First all of the odd-numbered lines are scanned (1,3,5,7,9,11, etc.) - creating the first field, then all of the even-numbered lines (2,4,6,8,10,12, etc)are scanned to create the second field. This method was employed when TV began in order to increase the apparent number of images per second from 30 to 60 to eliminate "flicker".

    Progressive scanning
    ... the scanning of a video image in which all of the scan lines are scanned in succession - 1,2,3,4,5,6,7,8,9, etc. When this scanning method is employed, the scanning rate (the # of scan lines per second) must be doubled. NTSC television scans at a 15,750Hz rate. In order to employ any device that produces 480p scanning format video, the TV set must be capable of scanning at 31,500Hz (approximate).

    Resolution
    ... as it applies to a video display, it describes the capability of the electron beam(s) to turn on and off very rapidly as they sweep across the screen - which results in the ability of the display to show fine detail. In order to measure this capability, a test pattern is employed that consists of vertical white stripes (with blank spaces in between them) all across the screen. The number of white stripes that can be differentiated constitutes the "resolution" of the display.

    The scanning formats that will be encountered are:
    480i - TV broadcasts, VHS and S-VHS videotape, DVD, DBS satellite
    480p - Progressive scan DVD players, EDTV broadcasts (FOX)
    540p - Upconverted (in a TV set) from 480i or 480p
    720p - an HDTV broadcast (ABC network)
    1080i - HDTV broadcasts (everybody else) - OTA and via satellite
    1080p - a HiDef format that may or may not ever come into usage

    These describe the number of scan lines that make a video frame, and whether it's interlaced (i) or progressive (p) scanned.

    The resolution is a quality that's inherent in the medium and in the display itself. But the display, no matter what it's resolution capabilities are, cannot display any more detail in the image than what's available from the program source.

    The resolution capabilities of the various mediums are:
    VHS videotape - 240 "lines of resolution" - 480i scan format
    NTSC (analog) television - 330 "lines of resolution" - 480i scan format
    S-VHS videotape - 400 "lines of resolution" - 480i scan format
    DBS satellite (SDTV signals) - 400 "lines of resolution" - 480i scan format
    DBS satellite (HDTV signals) - 960 "lines of resolution" - 1080i scan format
    DVD player - 540 "lines of resolution" - 480i or 480p scan formats
    FOX network EDTV - 960 "lines of resolution" - 480p scan format
    HDTV television - 960 "lines of resolution" - 720p or 1080i scan formats

    It has to be borne in mind that no matter what a given format or display is capable of, does not necessarily guarantee that you will get that much "resolution" from it. Often (usually, really) it's considerably less than the maximum "rez" available.

    Hope this brings the subject of "resolution" into sharper and clearer focus for everyone, and reduces misunderstanding ...

    Any questions?




    woodman
    woodman
  • John Holmes
    Moderator Emeritus
    • Aug 2000
    • 2703

    #2
    Very good post. And welcome to the Guide!




    "I came here, to chew bubble gum and kickass. And I'm all out of bubble gum!!!" My DVD's
    "I have come here, to chew bubblegum and kickass. And I'm all out of bubblegum!!!"

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    • George Bellefontaine
      Moderator Emeritus
      • Jan 2001
      • 7637

      #3
      Hi, Woodman, intelligence is always welcomed here. I look for to more interesting posts by you.




      My Homepage!
      My Homepage!

      Comment

      • David Meek
        Moderator Emeritus
        • Aug 2000
        • 8938

        #4
        Hi Woodman, welcome to the Guide! Nice startup post there fella.




        David - HTGuide flunky
        Our "Theater"
        Our DVDs on DVD Tracker

        .

        David - Trigger-happy HTGuide Admin

        Comment

        • Eduardo
          Moderator emeritus
          • Jun 2002
          • 1258

          #5
          great job on the primer. We alway appreciate knowlable posts.




          http://home.nc.rr.com/ejimenez

          Comment

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