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Pixels On Screen

  1. Jun 9, 2008 #1
    Theoretically in daily life we come across the word pixels like mega pixel camera or on computer screen or on T.V. we watch the pictures clearly due to large no. of pixels.But following questions come to my mind regarding this
    1.) What is mean by the word pixel and how can we understand it ?
    2.) Why we get multi colour on screen (computer or T.V.) ,while in physics lab on CRO, i get some greenish colour fluorescene.
    if u know more interesting and curious fact regarding this,let me know please.
    with regards
  2. jcsd
  3. Jun 9, 2008 #2
    The word pixel stands for Picture Element. (Picture Element)

    Wikipedia has a good article, with some pictures to guide you through. As for your second question I have no idea...

    [Wikipedia Article]
  4. Jun 9, 2008 #3


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    To get monochrome TV (one color only, whether it is white or green or whatever), there is only one color of phosphur coating inside the faceplate, and the electons hitting the phosphur is what causes the glow. In a color TV, there is a very clever arrangement of a "shadow mask" layer before the inside of the faceplate, and the shadow mask only allows electrons from each of the 3 electron guns to hit the appropriate color phosphur dot (there are red and green and blue phospur dots coating the inside of the faceplate in a color TV).

    Kind of hard to explain without pictures -- here's a link to an article that should help:

    Last edited: Jun 9, 2008
  5. Jun 9, 2008 #4


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    On older CRT rear projection TV, 3 seperate CRT are used, one red, one green, and one blue. The main advantage is that there is no mask or fixed pixel size, since the beam width and sweep rate are variable. Standard DVD's (480p) and standard NTSC broadcasts will look better on a CRT rear projection, because there's no upconversion to re-pixelate the image onto a fixed pixel screen, such as LCD, LCOS, or Plasma type screen. The hi-def pictures also look good, and you can get true "blacks". Link to a pro and con section:


    Monochrome monitors are usually white or green on black background. Green is easier on the eyes. Some applications don't need moving or scrolling text, and could use terminals like the IBM 3270. The monitor used a high persistance (took a long time to fade away) green phosphor, combined with a very narrow beam, which produced an extremely clean text oriented screen.

  6. Jun 10, 2008 #5

    Andy Resnick

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    It's also worth pointing out that the color information is encoded for (analog) television transmission in an incredibly complicated (some would say highly elegant) scheme:

    "Principles of Color Television, Hazeltine Laboratory Staff (Wiley, 1956).

    The wiki article doesn't fully convey the huge amount of science involved- deciding how to represent a non-spectral color like brown, for example; or how the color encoding was chosen based on vision.

    I have no idea how the digital broadcast specification transmits the information.
  7. Jun 10, 2008 #6


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    Even more elegant it allows exisiting BW sets to continue to receive a BW signal while layering the colourdata on top. It also fits all the colour data into less bandwidth than the BW signal.

    Basically the same as a DVD. It uses a jpeg technique where the picture is cut into small (8*8) pixel blocks and then fourier transformed to only store the most significant spatial frequencies.
  8. Jun 10, 2008 #7


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    A "pixel" (defined above as a picture element) can be thought of as a small element that can reproduce one color. When you have thousands or millions of them together, all displaying the necessary color, you can display an image. Individual pixels can be seen up-close on large LCD and Plasma televisions (or LCD projection TV's).

    A megapixel is defined as 1 million pixels. Note that the highest resolution HD-TV's on the market right now have an HD resolution of 1080p, which is 1920*1080 pixels. This equates to 2.07 megapixels (1920 x 1080 = 2073600). Standard DVD's have a resolution of 480p, which is 720x480 or 0.34 megapixels; HD-DVD's and Blu-Ray discs use 1080p.

    Wikipedia Article on 1080p
  9. Jun 10, 2008 #8
    You can actually get 3,840 x 2,160 pixels with the new samsung 82-inch lcd, but I don't think it has been released just yet.
  10. Jun 10, 2008 #9


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    Higher reolution displays definitely exist, espcially in computer monitors. The Dell 30" LCD has a 2560x1600 native resolution; some high-end drafting monitors can probably go much higher.

    My 8 year old 19" Trinitron CRT can display a max resolution of 1800x1440 (albeit only at 70 hz), and high-end 21" displays of the same period could display 2048x1536. The mark of a good gaming display back then was being able to display 1600x1200 or higher at 85hz.
    Last edited: Jun 10, 2008
  11. Jun 14, 2008 #10

    DVD uses a digital standard known as MPEG layer II, this stands for Motion Picture Expert Group,

    the format is put inside of a "container" as multiple program streams, usually one video and one audio, on the audio side Program Stream (but under the ISO/IEC 13818-1 standard it also includes a transport stream which can be seen in DVB-T/C/S or in HDV .m2t implementations) can use multiple types of digital audio compressions: LPCM, MP2, AC3 48kHz @ 5.1 surround and max 448kBits

    The video is made up of GOP (18 for PAL, and 15 for NTSC) structure that inlcudes the I/P/B intra frame compression.

    erh yes and it goes on... :D
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