Is standard broadcast 525i or 480i?

Discussion in 'Displays' started by Ken Burkstrum, Apr 18, 2006.

  1. Ken Burkstrum

    Ken Burkstrum Stunt Coordinator

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    If it's true, im wondering why broadcast looks worse then DVD?
     
  2. Joseph DeMartino

    Joseph DeMartino Lead Actor

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    Each NTSC frame consists of 486 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). That's the maximum resolution. Then you have to consider the source material, e/m interference in broadcast signals, compression in network satellite distribution, DBS retransmission, cable delivery, and a whole host of other things that can conspire to reduce the overall picture quality of "regular" TV. It isn't all about resolution. A lousy video tape played back on an HD channel would look worse than on an SD channel, because the HD broadcast would show the flaws more clearly

    Regards,

    Joe
     
  3. JeremyErwin

    JeremyErwin Producer

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    analog broadcast tv (ntsc) has a flawed color model. It's 480i, but it's inferior to dvd or non-bitstarved sdtv
     
  4. Ken Chan

    Ken Chan Producer

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    And it's not just the number of lines, it's also the amount of detail per line. VHS has the same as broadcast and DVD, but it looks worse than both. Laserdisc too, but it is between broadcast and DVD.
     
  5. Ken Chan

    Ken Chan Producer

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    dupe
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    Broadcast is crippled by many factors including just plain noise via broadcasting, it's often bounced around by satellite heavily compressed before it even gets broadcast locally to you, so you can get tons of banding and crap that way, MPEG blockin artifacts and all that. Also, as mentioned above, it is composite NTSC, while DVD is YCbCr, so DVD has a significant advantage there.
     
  7. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Broadcast has more horizontal resolution compared to VHS but less than DVD. Roughly 100 more lines versus VHS and 200 less lines versus DVD.

    A pristine NTSC broadcast signal from a satellite looked close to Laserdisc quality ... but you'd only see it if you had a big ugly dish.

    Regards
     
  8. Ken Burkstrum

    Ken Burkstrum Stunt Coordinator

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    I thought VHS was 320x240?

    "Broadcast has more horizontal resolution compared to VHS but less than DVD. Roughly 100 more lines versus VHS and 200 less lines versus DVD."

    Can you give me exact numbers?

    So broadcasted HD gets some of the same interference as standard broadcast yet is still preferable to playing a DVD in your home with a dvd player?

    Why would VHS look worse on a hd tv then on a sd tv, I figured despite any scaling they would look pretty much the same, like crap!
     
  9. JeremyErwin

    JeremyErwin Producer

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    so many questions.

    Let's start with resolution. With analog, there's no fixed horizontal resolution. It varies from set to set, and signal to signal. To measure horizontal resolution, the engineer throws up a test pattern, and counts the number of discernible lines.

    However, because of the way the signal is generated, there's always a standard number of scanlines, most of which hold picture data.

    Analog 480i uses 525 scanlines.
    Analog 720p (yes, if you use a RGB monitor and a tuner with a SVGA port, you can receive this...) uses 750 scanlines.
    Analog 1080i uses 1125 scanlines. (Japan had a analog HDTV system at one time)

    However, if you use a digital system to display or transmit a video signal, the horizontal resolution is defined. Both mpeg frames and LCD displays consists of a fixed number of picture elements.

    SDTV (480i) is 480x720.
    HDTV (720p) is 720x1280
    HDTV(1080i) is 1088x1920.

    DVDs store their picture at a variety of resolutions (640x480, 704x480, 720x480).

    So when someone says that VHS has a resolution of 240 lines, they mean that only 240 vertical black and white stripes can be distinguished. Any higher, and it all turns into a grey blur. Laserdisc is capable of about 500 lines of resolution. Both, however, display 525 scanlines (interlaced).

    There's a couple of ringers to toss in though. When measuring resolution, many (most?) measurements only care about a circular area of the screen. So, those 500 lines of resolution quoted for laserdisc may mean that the signal, when captured digitally, is best captured by a 665x480 digital frame.

    But analog television is dead, dead, dead.

    A common projector advocated on this forum is the Infocus 4085. It is a 16:9 projector, and it has a 480x852 (IIRC) element display. Some people have had some success sending a 720x1280 scaled image to the projector, thus taking advantage of the extra horizontal resolution of this display.

    Throw is color resolution and it gets even dicier.
     
  10. Ken Burkstrum

    Ken Burkstrum Stunt Coordinator

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    I'm confused what the difference between digital and film is because they both seem to be captured on tapes as far as I understand it. So your saying VHS film isnt made out of pixels and scanlines and that it's quality is comparable to 240 scanlines?
     
  11. JeremyErwin

    JeremyErwin Producer

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    VHS isn't film. It's magnetic tape. And it's generally analog (the exception being DVHS, which records mpeg2).

    You're confusing lines of resolution (columns) with scanlines (rows). Vhs, laserdisc, ntsc, dvd, all have the same number of scanlines (486). The number of lines of resolution varies from device to device.

    and, why, for the love of ... are we discussing vhs? vhs is obsolete. Gone. Forgotten. Even DVHS has been largely replaced by hard disc recordings and now HD-DVD.
     
  12. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    All horizontal numbers are expressed as lines per picture height. A square.

    VHS was 240 lines
    Broadcast was 340-350 lines
    Laserdisc was 375-425 lines
    SVHS was 400 lines
    DVD is 540 lines

    VHS looks crappy on HD sets because of the lack of scan line structures. Our brain interprets a sharper image when visible scanlines are present in an image.

    An interlaced picture of a white wall devoid of detail will look more detailed / sharper than a progressive scan image of the same white wall.

    Regards
     
  13. Allan Jayne

    Allan Jayne Cinematographer

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    Both 525i and 480i are used to refer to the same thing in analog video.

    For digital 480i video including DVD only 480 of the 486 picture containing lines are kept and lines 487 through 525 are not recorded on the disk either. For outputting an analog signal including component video the player adds back in scan lines 481 through 525 for both 480i and 480p. The various digital video formats SDMI and DVI and the way the data is recorded on DVD also have something between scan line 480 and the next frame's scan line 1 but this block of data is not organized as a fixed number of additional scan lines.

    Analog video is pixellated in the vertical direction only. If you were to take an upright thin cross section you may well see the cross section divided up into 480 or 486 pixels (720 or 1080 for HDTV). Digitial video including DVD is pixellated both horizontally and vertically.

    Video hints:
    http://members.aol.com/ajaynejr/vidres.htm
     
  14. Ken Chan

    Ken Chan Producer

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    352x480, not 640x480.
     
  15. JeremyErwin

    JeremyErwin Producer

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    I stand corrected. The nicest thing about atsc, imho, is that it doesn't have ntsc's broken color model.
     
  16. Allan Jayne

    Allan Jayne Cinematographer

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    What shows are recorded on DVD as 352 pixels across (by 480 high)?

    They must look awfully blurry.
     
  17. Ken Chan

    Ken Chan Producer

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    They are blurry. I don't know of any DVDs that are sold that way, but it's in the spec, and it works. The big thing is you can get about twice as much stuff on a disc. Maybe if you're transfering from VHS, it makes the bad only slightly worse. Come to think of it, maybe some DVD-recorders use it for their long-play setting.
     
  18. ChrisWiggles

    ChrisWiggles Producer

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    This is misleading, IMO. All video is sampled in both directions. I also would refrain from using "pixel" terminology, but rather image sampling. Pixels is a slightly confused term.
     
  19. MarkHastings

    MarkHastings Executive Producer

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    Is 352x480 the DVD spec? I thought it was an MPEG spec?

    Anyways, you find that spec mostly with DVR's - That's how you get more shows recorded onto the hard drive.

    Also, VOD (Video On Demand) is often recorded to sizes lower than 720x480 to make it easier to deliver.
     
  20. Steve Berger

    Steve Berger Supporting Actor

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    352x480 and 720x480 are in the DVD spec (I think 704x480 is also but I'm not positive). Consequently most authoring programs will make DVDs from them quite nicely.

    Since 352x480 is better than most consumer tape formats and slightly better than the typical analog broadcast available, it is, in theory, a good choice for recording those things.

    The VOD (528x480 and 540x480 commonly) allow reduced bandwidth for transmission but the files generally need transcoding (or header changes) to create DVDs. Digital camcorders (at 720x576) also require similar jiggering to create DVDs.

    DVRs use various resolutions and bitrates but are fairly secretive about it. You find out when you examine the files created. Some of the flex recordings can even change during the recording process, as I understand it, making DVD creation really tough (if you can extract the files).
     

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