Color Depth - Bits per Pixel

The amount of color information in a picture is usually referred to as the color depth or the number of bits per pixel. For a given picture size, the bigger the color depth, the more colors that can be represented and the more memory and file storage space that the image will require.

• Bits and Bytes - Each memory location in a computer can hold a piece of information called a byte. Each byte consists of 8 bits.

 
• Pixel - Refers to a picture element or one dot in the image. Each computer bit can be either off (0) or on (1). The computer converts this "on-off" data into color information. The more bits used for each pixel, the more colors that can be used to draw the pixel.

 
• 1 bit per pixel (two colors) . . .
  0 - black
  1 - white
  Although each pixel must be either "on" or "off", patterns of pixels can be used to give the illusion of various shades of grays. This type of image is most suitable for line art.

 
• 2 bits per pixel (four colors) . . .
  00 - black
  01 - dark gray
  10 - light gray
  11 - white
  The four different bit combinations can be assigned to any combination of colors. They need not be the shades of gray indicated here. The four different shades of gray are typically used for "cheap newspaper images"

 
• 4 bits per pixel (sixteen colors) . . .
  0000 - black
  0001 - red
  0010 - green
  0011 - yellow
  0100 - blue
  0101 - magenta
  0110 - cyan
  0111 - white
  1000 - etc.
  "cartoon" art

 
• 8 bits per pixel (256 colors) . . .
  "clip art" & low res pictures


• 24 bits per pixel (millions of colors) . . .
  continuous tone (photographs)


• All scanners will scan at least 24 bits per pixel.

 
• Many scanners will scan at 36 bits per pixel or higher.

 
• Most paint programs can handle no more than 24 bits per pixel.

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Comments and suggestions should be sent to:
email: sturges@iastate.edu
phone: 515-294-6242.

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© 2001, Leroy D. Sturges
( This document was last updated on )