How do you compare computer and tv resolution?

Discussion in 'Archived Threads 2001-2004' started by Travis Calloway, Dec 3, 2002.

  1. Travis Calloway

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    I know some things about tv but know very little about computers. My friend is an expert in computer but knows nothing about tv. When we discuss about movie or image resolution, we couldn't communicate.

    For example, with computer let say you get 1024x768 image. That's the vertical and horizontal pixels right? But what happens when you play a movie on such a screen? When we talk about vcr, dvd, HDTV and the likes, we go into horizontal lines of resolution interlaced or progressive. How does that compare? If you freeze an image on tv from a 480i, 480p or 1080i source and so on, what resolution are we getting? Any help will be appreciated.
     
  2. ManW_TheUncool

    ManW_TheUncool Producer

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    I'm more of a computer person, but from what I understand, you really can't translate the same thing into the analog/CRT-based video world--not exactly anyway. Basically, the vertical resolution in the analog/CRT-based video world is not set clearly like in the computer world. Standard horizontal resolutions are 480i, 480p, 720p and 1080i, but actual vertical resolution varies depending on the analog signal and the display's capability. Of course, if you're talking LCD-based or something like that, you do have fixed resolution in terms of pixels at least for the display itself.

    Nevertheless, it's meaningful enough to talk about DVD's resolution in terms of pixel resolution. DVD is capable of 720x480 resolution natively. If you display this on a computer display in some other resolution, you'll need to do some amount of scaling.

    With analog video formats like VHS, 8mm, Hi8, SVHS and LD, you can only approximate their vertical resolution compared to pixel resolution. VHS and 8mm would be roughly 320x480i, SVHS, Hi8 and LD are roughly 540x480i. Do note that these are based on their maximum, standard capability and does not reflect actual performance of the media, etc. And various manufacturers claim higher vertical resolutions w/ enhanced versions of these formats, but I've never looked into the facts about them.

    Hope this helps.

    _Man_
     
  3. Brae

    Brae Supporting Actor

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    Travis, in order to equate the equivalent resolution of a television to that of a computer CRT two things needs to be known: number of lines and aspect ratio.
    For nistance, let's say you have a conventional NTSC television that has 480 lines. NTSC has an aspect ratio of 4:3. What this means is that for 3 lines of resolution there is an approximate 4 units of horizontal resolution.
    The the approximate resolution of an NTSC television is about 640x480. The 640x480 resolution also happens to be known as VGA ni the computer world, which is followed by SVGA (800x600), XGA (1024x768), and so on.
    Now, high-definition televisions following the ATSC motto are using the 16:9 aspect ration instead of the 4:3. Thus, a HDTV with 1080 lines of resolution is said to have a virtual resolution of 1920x1080.
    I used the term virtual resolution in that some products are better at achieving this than others. Also, you may get confused in the middle of some of this (I do!) when someone starts talking about the 720x480 resolution of DVD, which has an aspect ratio of 3:2!
    Then still there are other things you need to keep ni mind like interlaced and non-interlaced (progressive. NTSC televisions are said to be interlaced, while ATSC (HDTV) are/may-be progressive in nature.
    Looking at the lines of your television, label them:
    1 ==============================================
    2 ==============================================
    3 ==============================================
    4 ==============================================
    5 ==============================================
    6 ==============================================
    7 ==============================================
    8 ==============================================
    In NTSC you get to see ONLY the ODD numbered lines first and then the EVEN numbered lines next:
    1 ==============================================
    2
    3 ==============================================
    4
    5 ==============================================
    6
    7 ==============================================
    8
    1
    2 ==============================================
    3
    4 ==============================================
    5
    6 ==============================================
    7
    8 ==============================================
    But in many HDTV's nuder the ATSC spec you should be able to see ALL the lines at the same time, thus yielding twice the information:
    1 ==============================================
    2 ==============================================
    3 ==============================================
    4 ==============================================
    5 ==============================================
    6 ==============================================
    7 ==============================================
    8 ==============================================
    Computer monitors are progressive in nature, and it is not uncommon to find a computer monitor capable of having a much higher resolution than your typical Wal-Mart television. This is a good thing, otherwise we wouldn't be able to get so much porn no our screens. [​IMG]
     
  4. ManW_TheUncool

    ManW_TheUncool Producer

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    Yep, that's supposed to be the standard way of quoting vertical resolution, ie. adjusting for the aspect ratio.
    However, you'll find that some manufacturers do NOT stick to this method, so sometimes you find one TV w/ specs quoting much higher vertical resolution than another even though they actually have roughly the same resolution capability (or maybe even worse!).
    Furthermore, the specs provided for the individual TVs are just rated specs, which probably do not reflect real-world performance. It's kinda like when speaker manufacturers claim 20-20Khz frequency response even for a $50 speaker OR like when CDROM makers claim 50x max read and/or write speed. [​IMG]
    _Man_
     
  5. Brae

    Brae Supporting Actor

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    True, very true. But, I would tend to think of the common Wal-Mart $179 special than those units with higher number of lines. Still, your point is very accurate. To find the psuedo-resolution of a television, one only needs to know the number of lines and then multiply that number by the decimel-equivalent of the aspect ratio to get the horizontal resolution.

    Hence, for a TV with 480 lines in a 4:3 ratio unit the psuedo resolution would be:

    (480)(4/3) x 480 = (480)(1.33) x 480 = 640 x 480

    If one's television is 4:3 then simply replace the 'Z':

    (Z)(1.33) by (Z) for its psuedo resolution.
     
  6. Allan Jayne

    Allan Jayne Cinematographer

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    The computer 640 x 480 resolution has 480 visible scan lines and the computer's video card always supplies each line with details 1/640'th the screen'w width. The computer 800 x 600 resolution has 600 visible scan lines and the computer's video card always supplies each line with details 1/800'th the screen width. However a CRT computer monitor accepts video with, say, 480 or 600 or 768 visible scan lines but doesn't care how finely spaced the details are across each scan line, things will be spaced out right. If the monitor accepts the above scan line counts, it may or may not also accept 240, 540, and 720 scan line video which are used in regular TV and HDTV broadcasts. (The 480i and 1080i formats are treated by a monitor as 240 and 540 where the monitor should stagger every other "frame" to give the appearance of 480 and 1080 scan lines respectively. If the monitor does not do the staggering, your vertical resolution as seen is cut in half.)
    The monitor may be putting picture details every 1/1024'th the screen width and every 1/768'th the screen height but the resolution as seen will be less if the electron beam spot is too big. As someone else on this forum mentioned, such a monitor has 1024 x 768 addressable resolution (actually anything x 768 for a CRT) but less than 1024 x 768 visible resolution. Visible resolution as "lines of resolution" (dark and light dots in a row or dark and light dots in a column) correctly must specify some distance. For video all textbooks and technical journals use as the distance the smaller dimension of the screen i.e. the height. About the "pseudo pixel resolution" of analog video, for example, VHS being 480 x 320, the limitation is the the spot width, regular VHS can't make spots smaller than 1/320'th the screen width but can position them at much (infinitely) finer increments across the screen.
    For an LCD or other fixed pixel computer monitor, the monitor's own circuits usually spread out (scale) the incoming scan lines to fill all the rows of pixels. For example if the monitor has 768 rows of pixels and you feed in video with 480 scan lines per frame, three out of every five incoming scan lines will be used twice. (More sophisticated circuitry will do blending to make the picture smoother). If each row of pixels has 1024 of them across and the incoming video has details 1/720'th the screen width, some (about 2 out of every five) details 1/720'th the screen width occupy two pixels and some occupy just one so that everything is evenly spaced and all the pixels across are filled.
    While 720 x 480 resolution for a DVD may suggest a 3:2 aspect ratio, video can be stretched any which way. The term used is non-square pixels. Both standard (pictures meant to be 4:3 including black bars) and anamorphic (pictures meant to be 16:9 including any remaining black bars) use the same 720 x 480 (sometimes 704 x 480) resolution.
    Doing "freeze frame" on a VCR and on most LD players with that capability for a "CLV" (long play) disk, you see just the odd lines (each used twice) or just the even lines (each used twice). Freeze frame on DVD or for an LD player using a "CAV" (standard play) disk shows all 480 scan lines.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     

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