What is native resolution?

Discussion in 'Displays' started by Scott Stephens, Sep 2, 2004.

  1. Scott Stephens

    Scott Stephens Stunt Coordinator

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    I'm still trying to take all of the HDTV lingo in before I buy a set...I've heard many references to "native resolution"--what is this and what significance does it have when buying a set?

    Also, if anybody knows of an "HDTV Buyer's guide" or a link to a thread with some basic HDTV definitions/information, I'd appreciate it. Thanks.
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    Native resolution is the resolution in terms of pixels across and pixels down and based on what the TV's circuitry works with and what the display elements (picture tube, etc.) show.

    Almost all non-CRT display elements are subdivided into pixels so we might think that the native resolution is always the number of pixels across and number of pixels down on the display element. A typical plasma standard definition TV has 858 pixels across and 480 down. A data grade SVGA projector has 800 pixels across and 600 down.

    Analog TV sets and monitors have native vertical resolution(s) but not native horizontal resolution. Some experts say an ordinary NTSC TV has native resolution of 480 down (480 visible scan lines) but infinite across, since a single spot or pixel can be put in an infinite number of possible positions horizontally. An analog TV can display DVD programs with 720 pixels across just as well as broadcasts with at most 440 picture details across assuming it can make spots as small as 1/720'th the screen width. Other experts would argue that the native horizontal resolution for analog video is the maximum number of distinguishable spots that can be put on a scan line, maybe 500 for a particular TV set. Some analog TV sets, notably front projectors may have a range of "native vertical resolutions", better referred to as scan rates, for example anything from 480p to 1080p and synchronizing themselves to the input.

    But sometimes the electronics works with a different pixel count. In this case the native resolution would be at most the lesser of the pixel count used by the electronics and the pixel count of the display element. One model of LCD TV has an LCD panel 1068 pixels across and 480 down, but the electronics process only 640 across and 480 down. The native resolution is 640 x 480. Experts will also argue here. If the electronics process video as 640 x 480 only and the LCD (or DLP) element has 800 x 600 pixels, there will be some non-uniformity in the finished picture since 640 does not go evenly in to 800 and 480 does not go evenly into 600. Some experts will argue that there is no native resolution for that particular TV set.
     
  3. Rolando

    Rolando Screenwriter

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    Actually I have been meaning to ask, do RPTV have a native resolution to match HDTV?

    I mean I am looking at getting a Tosh 51hx83 or a Hitachi 51s500 and they claim HDTV compatibility but will an HDTV signal really display at 1080? Or is it really on "compatible" and downgrades HD signal to it's native resolution so we never really get a real HD resolution?
     
  4. Allan Jayne

    Allan Jayne Cinematographer

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    A good high definition RPTV with CRT's will put up 1080 scan lines in unique positions and can put pixels in any of 1920 positions horizontally which represents the full resolution of 1080i. In practice, the smallest spot displayable is bigger than 1/1080'th the screen height or 1/1920'th the screen width so a defacto optical degradation occurs.

    Some experts will argue that the above described TV does have a native resolution of 1920 x 1080. Others will disagree.

    A typical plasma or DLP HDTV has a display element with 720 rows of pixels each row subdivided into 1280 individual pixels. The 1080i program material is specifically downconverted. Good downconversion will yield a native resolution of 1280 x 720 matching the display element. There exist poorer downconversions with resolution of 1280 (or less) x 540 for the 1280 x 720 display, since 1080i comes in as fields (half pictures) of 540 scan lines each. With such a poorer downconversion, the resulting native resolution is now smaller than the display element resolution.

    Perhaps I am making the subject of native resolution overly complicated, but it is important to understand that native resolution depends on more than the pixels in the display element.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    I don't think Allen is making this overly complicated, because it is inherently complicated and confusing.

    Basically, there are two different things going on. One is the resolving capabilities of a particular display, which encompasses the "native resolution" (if there is one, I for one would argue that projection CRT devices have no such native resolution as Allen covered somewhat).

    The second is the electronic capabilities.

    What makes this so confusing is within #1, as mentioned with non fixed-pixel devices (CRTs), there may not be a set-in-stone "native resolution" as there is with a digital projector for instance, where the native resolution is how many pixels are on the LCD panels or the DLP chip(s). Then, what video inputs are accepted, and how they are handled add to the complications.

    With fixed pixel displays, there is a clearly defined number of pixel elements that create the picture, and all the inputs are scaled to this resolution. Oftentimes, higher resolutions are accepted, but must be scaled down to the native resolution because of course there are not that many pixel elements to display the higher resolutions. With fixed pixel devices, understanding this is simpler, because you have a defined spec of the native panel resolution, and that is always your limit in resolution that you can resolve.

    With CRT projection, this becomes more complicated. First, some displays, such as many CRT front-projectors, have no scaling at all, and are multi-sync to pretty much anything. They simply display what you feed them. In consumer RPTVs that are CRT-based, skimping on the electronics means that often these sets will scale things to certain resolutions, such as 480p and 1080i, but may not be able to display 720p for instance, because of electronic limitations.

    Because, as allen noted, CRTs can be made to display many resolutions, and there are no real pixels, nor "native resolution" determining what is technically, properly resolved with CRTs is a little advanced. The sweetspot, which is what I consider analagous to a 'native resolution' will vary widely even among identical sets, because of electronics age, setup, etc. The tighter your beam focus, the more distinct scanlines you can display, thus the higher resolutions you can resolve.

    Add in the other issue of interlaced scanning, which is possible on CRTs for 1080i, whereas in digitals, you are dealing with progressive, fixed pixel panels, and you can see why discussing the native resolution of digitals is a little difficult to immediately compare to CRT displays. You can, but there isn't really a spec anywhere that will tell you the sweetspot of your particular CRT and its setup.

    With CRT-based RPTVs, you should read in detail the specs and reviews/manuals to understand fully which input resolutions are accepted, and whether they are scaled down or up to other resolutions. Oftentimes 720p is noticeably absent in being displayed, it often gets scaled to other things, since 720p is relatively hard to display with cheapo electronics.

    So in summary, if that long ramble made some sense, there are the resolutions that are accepted as inputs, then there are the resolutions that are displayed. And the final confusion added to that with CRTs, is more than just what is displayed, but which things that can be displayed that are being properly resolved.
     
  6. Steve Schaffer

    Steve Schaffer Producer

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    Panasonic's 1st generation HD-ready widescreen sets would display at 720p, they cost upwards of $6k for a 56" model.

    These days I don't know of a single crt based rptv that will do native 720p. In practical terms this is not really a problem except for X-Box fanatics as all HD receivers and cable boxes will convert 720p to 1080i and do it very nicely.

    All crt based HD-ready crt based rptvs have 1080i as one of the native scanrates. Most will accept 720p but those that do convert it to either 1080i or 480p. Again a moot point except for the X-Box.

    So any crt HD-ready rptv will indeed use a 1080i scanrate. No downconversion of that scanrate will occur in the set.

    Purists will state that the HD standard requires a certain pixel count over the entire surface of the screen. crt rptvs with 7" guns (the vast majority) and direct view crt sets won't display this many pixels, leading to claims that they aren't "true" hdtvs. This has nothing to do with scanrate, however, and in practice is pretty much meaningless as far as perceived pq.


    Many sets (Hitachi, Toshiba most notably) will display 540p or 1080i only, and not 480p, so any incoming 480p signal from a progressive scan player will undergo an additional conversion in the set. Others like Sony and I think Mitsubishi will still display 480p natively.

    JVC crt sets will only display 1080i--everything else is converted.

    Conventional wisdom usually is that the fewer scanrate conversions the better.

    The overriding fact, in my opinion, is that a good crt based rptv offers the absolute best bang for the buck as picture quality. Typical prices for 50+ inch models from most good mfgs is now well below $2k, typically well over a thousand dollars less than dlp or lcd, and with some minor tweaking they can produce a smoother more film-like image than the dlp and lcd models with deeper blacks.
     

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