idiot-level question about VP

Discussion in 'Displays' started by chuckg, Apr 28, 2004.

  1. chuckg

    chuckg Supporting Actor

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    Greetings!

    I have suddenly discovered that my house contains a home theater. Where the heck did that come from?

    Now that all the parts are in and working, the drool factor comes into play, and I *really* want to put in a front-projection screen. ( 4.5 feet tall, 8 feet wide, drool drool. ) That leads to a few idiot-level questions. (BTW, I'm an engineer in a planetarium with more than just a little audio/video technology, so it is terribly embarassing that I have to ask these questions!)

    Just what "resolution" is the HDTV standard delivering? Just what resolution does DVD *really* give? (sub question: in 4:3 , other ratios, and progressive scan ) What is the resolution of the digitalized version of NTSC? By these questions I mean how many dots tall, how many dots wide.

    What video projector actually projects these standards? (or for that matter, is there any "viewing device" that gives these resolutions) - So far they all seem to deliver quite a lot less. By that I mean, is there a device for which the native mode matches the source resolution?

    Finally, I am wondering why in the world I should run several sets of video cables all the way to my projector. Is there a consumer version of a head-end device that would do the switching and resolution matching and send the signal over one set of wires, in the projector's native mode? (in the pro world, such a device is called a seamless switcher, and they work just dandy.)
     
  2. Jonty Rees

    Jonty Rees Stunt Coordinator

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    Sony offers some kind of switch for video, (IFU-HS1), so I'm sure other manufacturers will also. You can probably also get a receiver that does all the switching and converting. My receiver is constrained to what-goes-in-must-come-out, but there must be newer ones that can handle anything in to anything out by now.
     
  3. Allan Jayne

    Allan Jayne Cinematographer

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    HDTV standard -- There are two in the U.S., 1920x1080 and 1280x720 both for 16:9 pictures. The corresponding 4:3 pictures are officially 1440x1080 and 960x720 with unused pixels on both sides.

    This means that a CRT based HDTV projector can place a single spot (its finest picture detail) in any one of 1920 positions across and 1080 positions up/down (if one of its native modes is 1080i). You are getting all 1080 scan lines. However only the best projectors (with 9 inch CRT's and 37 MHz video bandwidth) can make the spot small enough that three in a row of differing intensities can be distinguished. There may be some LCD or DLP projectors with 1920x1080 pixels and the native mode is 1920x1080 but without 37 MHz of bandwidth such a projector will be unable to make adjacent pixels abruptly contrasting in intensity.

    Deficiencies anywhere in the video signal path, from camera to studio processing to MPEG encoding to transmission to MPEG decoding to scaling to video amplifying to picture tube electron beams will affect what resolution you get.

    Some projectors put all their video inputs through a scaler of some sort even if the number of scan lines will stay the same. If the scaler chops up each 1080i scan line into fewer than 1920 parts (all scalers digitize), the native resolution of the projector is no longer 1920x1080.

    The MPEG encoding used in all HDTV and DVD production always has some loss of content. In terms of resolution three small juxtaposed details may be reproduced in some places in the picture but not in other places and these losses may vary at random and fortunately they are usually not highly obtrusive.

    Digitized NTSC will never have resolution better than what it had before, even if you are using 1080 scan lines and 37 MHz of bandwidth to process it. The best NTSC is that prepared for DVD and it allows 480 picture details vertically and picture details 1/720'th the scan line width horizontally.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  4. chuckg

    chuckg Supporting Actor

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    Many thanks, Allan. How is Nashua? Many moons ago I worked for Daddy's Junky Music (DJM Pro Audio) doing audio installations. That was after a couple years out on the coast doing lighting, carpentry, audio, etc at Prescott Park Arts Festival and Theatre by the Sea in Portsmouth.


    Your answer is the clearest and most complete response to my silly questions that I have ever seen. It fully explains, almost by accident, the little 480i and 720p that I see popping up now and then. If we would just use numbers instead of catchy phrases to indicate which of many sizes/resolutions/aspect ratios, then nobody would ever be confused!
     
  5. Bob McElfresh

    Bob McElfresh Producer

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    There is a product called an "IScan Pro" that will take Composite/SVideo/Component and convert it to Progressive (480p) so you only have to run 1 component cable to the projector.

    But be aware that some new digital cabling standards are starting up (DVI, HDMI) that you may want to be compatible with in the future.
     

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