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| In The Lab HDTV and Monitor basics: A screen odyssey by chris |
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Dave Bowman: "My God, it's full of stars!" (from 2001, A Space Odyssey) Whether we are looking at computer monitors or High Definition Television displays, it all comes down to the dots or pixels that flicker there. Each of the different monitor technologies, CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), or Plasma, still generate an image by turning small illuminated points on the screen on and off. By exciting tiny points of red, green, and blue phosphor you will perceive what appears to be a white dot visible on a CRT or Plasma screen. LCD screens display colors by passing or blocking white light through a red, green or blue filtered liquid crystal layer.All standard displays generate images using three colors of light: red, blue and green. Together, these three points are called a triad, and represent the smallest possible addressable point on the display. When looking at LCD and some other types of displays, you may see a specification for "native mode" or "native resolution." This refers to the screen resolution where one pixel generated by your video source uses only one triad of the display.
If the native resolution is 1024x768, there should be 1024 red, 1024 green and 1024 blue dots positioned in triad-groups horizontally across the screen. If you changed your screen resolution to something less than 1024x768, and did not "expand" or "stretch" the display, then you will see a black border around the image, with only the central 800x600 dots being used. If the display was set to expand the image, then some pixel information had to be ignored, while other points were represented more than once, just to fill the screen. The result is a fuzzy or ragged looking image, where some lines might appear too wide and others appear thin and sharp. If you are going to use your large screen TV as a computer monitor display, you want to set the video screen size to the best the screen can display, this will usually be identified as the native resolution of the display, even if it is lower than the HDTV resolution. For example, many of our large LCD and Plasma TV screens can display 1920x1080 HDTV resolutions, but only support 1280x720 as the best computer resolution. When working with any displays that have a single native resolution (this includes LCD, Plasma, and DLP), all resolutions except the native mode must be compressed or expanded to fit to display. "The monolith was 11 feet high, and 11/4 by 5 feet in cross-section. When its dimensions were checked with great care, they were found to be in the exact ratio 1 to 4 to 9 - the square of the first three integers." (Arthur C. Clarke, 2001: A Space Odyssey) The concept of screen ratio warrants mention as well. You may have noticed that many computer displays are getting wider, and TVs definitely are, with the marketing of HDTV as the must-have next generation standard. The plan is not specifically for HDTV to replace current broadcast TV, but for digital broadcasts to replace the analog radio frequency broadcasts that are still in use now. CRTs may appear to handle different resolutions better than LCD or other display types, mainly because the dot pitch or spacing between the phosphor dots is typically much smaller than with the other technologies. When choosing any display where dot pitch is specified, keep in mind that the small the number, the closer together the screen pixels will be. Pixels that are smaller and closer together can make your display appear sharper and the images clearer and better defined. (I say "can" and not "will" because the sharpest image is also based on the screen resolution you are sending to the display. If you operate your computer display at a screen resolution less than its highest level, you are displaying less information in exchange for making the image appear larger.) HAL9000: "I'm sorry Dave, I'm afraid I can't do that."
HAL9000: "It's puzzling. I don't think I've ever seen anything quite like this before." Many of the large format LCD, Plasma, or DLP (Digital Light Processing) displays have multiple connections for the video source. The type of connection you use may determine the quality of the image and the maximum resolution that is displayed. It seems that one of the common complaints of people buying a new High Definition TV is that the images they see at home don't look as good as the ones in the store. The obvious reason for this is that they are probably not using a high-definition video source. If you send a standard satellite, cable TV, or DVD signal to your display, the resolution is based on that NTSC standard of roughly 640x480. All you will get is a really big view of the same image you sent to your small screen. Even with a special (ATSC) HDTV tuner in the display, or when using an external HDTV decoder from your satellite or cable company, you need to select a connection method that will transmit the sharpest, highest-resolution signal to your display.
Shop Online: * DRM: Digital Rights Management. Already some HD resolution video can be blocked from being displayed on any device unless it can be transmitted in a digital format that supports anti-piracy features. This is supposed to prevent anyone from making exact digital copies of the media. |
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