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What is a Pixel? September 19, 2006

Posted by healthyself in Bytes, Cell phone safety.

“Short for Picture Element, a pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.”

“The number of bits used to represent each pixel determines how many colors or shades of gray can be displayed. For example, in 8-bit color mode, the color monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colors or shades of gray.”

“On color monitors, each pixel is actually composed of three dots — a red, a blue, and a green one. Ideally, the three dots should all converge at the same point, but all monitors have some convergence error that can make color pixels appear fuzzy.”

“The quality of a display system largely depends on its resolution, how many pixels it can display, and how many bits are used to represent each pixel. VGA systems display 640 by 480, or about 300,000 pixels. In contrast, SVGA systems display 800 by 600, or 480,000 pixels. True Color systems use 24 bits per pixel, allowing them to display more than 16 million different colors.”


“We can also use units to guide our computations of space requirements for multimedia applications. Consider the question of how much video RAM (Random Access Memory) is required for a given monitor (or display) setting. The display setting is specified by

  • the width and height (or resolution) in pixels (picture elements), and
  • the number of colors (depth) per pixel.

A typical resolution might be

800 pixels wide by 600 pixels in height,
with a depth of 65 thousand colors per pixel.

Vertical resolution is sometimes given in lines, so that the above would be denoted as 600 lines, each of which is 800 pixels wide. In this usage, a line is not a real unit; the resolution is computed by simplying multiplying the horizontal pixel resolution by the vertical line resolution, and the result is given in pixels. Thus a two dimensional video image is represented as a simple list of pixels; in this example, the computer would start a new line after every 800 pixels.

Since 65,536 is 2 16, we will need 16 bits for each pixel. We then compute the amount of video memory required:

  1. ? bytes = number of pixels * bytes per pixel
  2. number of pixels = 800 * 600 = 480,000 pixels
  3. bytes per pixel = 16 bits / pixel / ( 8 bits / byte ) = 2 bytes / pixel
  4. bytes of video RAM = 480,000 pixels * 2 bytes / pixel = 960,000 bytes



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