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What does screen resolution mean? The images displayed on monitor screens are composed of many small dots of light. These dots are called pixels or picture-elements. The number of pixels displayed by your computer system is known as the screen resolution. The resolution that you have depends on your video board and your monitor. On a low resolution screen, there are fewer pixels, so images are larger, and less well defined.
Resolution
Resolution is the number of pixels (individual points of color) contained on a display monitor, expressed in terms of the number of pixels on the horizontal axis and the number on the vertical axis. The sharpness of the image on a display depends on the resolution and the size of the monitor. The same pixel resolution will be sharper on a smaller monitor and gradually lose sharpness on larger monitors because the same number of pixels are being spread out over a larger number of inches.
A given computer display system will have a maximum resolution that depends on its physical ability to focus light (in which case the physical dot size - the pixel - matches the dot pitch size) and usually several lesser resolutions. For example, a display system that supports a maximum resolution of 1280 by 1023 pixels may also support 1024 by 768, 800 by 600, and 640 by 480 resolutions. Note that on a given size monitor, the maximum resolution may offer a sharper image but be spread across a space too small to read well.
Display resolution is not measured in dots per inch as it usually is with printers. However, the resolution and the physical monitor size together do let you determine the pixels per inch. Typically, PC monitors have somewhere between 50 and 100 pixels per inch. For example, a 15-inch VGA monitor has a resolution of 640 pixels along a 12-inch horizontal line or about 53 pixels per inch. A smaller VGA display would have more pixels per inch.
Pixel
A pixel (a word invented from "picture element") is the basic unit of programmable color on a computer display or in a computer image. Think of it as a logical - rather than a physical - unit. The physical size of a pixel depends on how you've set the resolution for the display screen. If you've set the display to its maximum resolution, the physical size of a pixel will equal the physical size of the dot pitch (let's just call it the dot size) of the display. If, however, you've set the resolution to something less than the maximum resolution, a pixel will be larger than the physical size of the screen's dot (that is, a pixel will use more than one dot).
The specific color that a pixel describes is some blend of three components of the color spectrum - red, green, and blue. Up to three bytes of data are allocated for specifying a pixel's color, one byte for each color. A true color or 24-bit color system uses all three bytes. However, most color display systems use only eight-bits (which provides up to 256 different colors).
Screen image sharpness
Screen image sharpness is sometimes expressed as dots per inch (dpi). (In this usage, the term dot means pixel, not dot as in dot pitch.) Dots per inch is determined by both the physical screen size and the resolution setting. A given image will have less resolution - fewer dots per inch - on a larger screen as the same data is spread out over a larger physical area. Or, on the same size screen, the image will have less resolution if the resolution setting is made larger - resetting from 800 by 600 pixels per horizontal and vertical line to 640 by 480 means fewer dots per inch on the screen and an image that is less sharp. (On the other hand, individual image elements such as text will be larger in size.)
Dot Pitch
The dot pitch specification for a display monitor tells you how sharp the displayed image can be. The dot pitch is measured in millimeters (mm) and a smaller number means a sharper image. In desk top monitors, common dot pitches are .31mm, .28mm, .27mm, .26mm, and .25mm. Personal computer users will usually want a .28mm or finer. Some large monitors for presentation use may have a larger dot pitch (.48mm, for example). Think of the dot specified by the dot pitch as the smallest physical visual component on the display. A pixel is the smallest programmable visual element and maps to the dot if the display is set to its highest pixel. When set to lower resolutions, a pixel encompasses multiple dots.
Technically, in a cathode ray tube (CRT) display with a shadow mask, the dot pitch is the distance between the holes in the shadow mask, measured in millimeters (mm). The shadow mask is a metal screen filled with holes through which the three electron beams pass that focus to a single point on the tube's phosphor surface. In CRTs that use an aperture grill (a slotted form of mask), such as Sony's Trinitron flat-screen technology, the dot pitch is the difference between adjacent slots that pass through an electron beam of the same color.
For more information on glossary terms, click the Windows Start button and choose Help. Select the Index tab and type in screen or resolution as a keyword. It's that simple!
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last modified
Monday December 20 2004
© 2000 - David Seibold
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