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data representation in computer science |
Data Representation
Information
today comes in different forms such as text, numbers, images, audio, and video.
Text :
In data
communications, text is represented as a bit pattern, a sequence of bits
(0s or 1s). Different sets of bit patterns have been designed to represent text
symbols. Each set is called a code, and the process of representing symbols is
called coding. Today, the prevalent coding system is called Unicode, which uses
32 bits to represent a symbol or character used in any language in the world.
The American Standard Code for Information Interchange (ASCII), developed some
decades ago in the United States, now
constitutes the
first 127 characters in Unicode and is also referred to as Basic Latin. Appendix
A includes part of the Unicode.
Numbers
:
Numbers are
also represented by bit patterns. However, a code such as ASCII is not used to
represent numbers; the number is directly converted to a binary number to
simplify mathematical operations. Appendix B discusses several different
numbering systems.
Image
:
Images are
also represented by bit patterns. In its simplest form, an image is composed of
a matrix of pixels (picture elements), where each pixel is a small dot. The
size of the pixel depends on the resolution. For example, an image can
be divided into 1000 pixels or 10,000 pixels. In the second case, there is a
better representation of the image (better resolution), but more memory
is needed to store the image.
After an image
is divided into pixels, each pixel is assigned a bit pattern. The size and the
value of the pattern depend on the image. For an image made of
only black and-white dots (e.g., a chessboard), a 1-bit pattern is enough to
represent a pixel.
If an image
is not made of pure white and pure black pixels, we can increase the size of
the bit pattern to include gray scale. For example, to show four levels of gray
scale, we can use 2-bit patterns. A black pixel can be represented by 00, a
dark gray pixel by 01, a light gray pixel by 10, and a white pixel by 11.
There are
several methods to represent color images. One method is called RGB, so
called because each color is made of a combination of three primary colors:
red, green, and blue. The intensity of each color is measured, and a bit
pattern is assigned to it.
Another method
is called YCM, in which a color is made of a combination of three other primary
colors: yellow, cyan, and magenta.
Audio :
Audio
refers to the recording or broadcasting of sound or music. Audio is by
nature different from text, numbers, or images. It is continuous, not discrete.
Even when we use a microphone to change voice or music to an electric signal,
we create a continuous signal.
Video :
Video refers to the recording or broadcasting of a picture or movie. Video
can either be produced as a continuous entity (e.g., by a TV camera), or it can
be a combination of images, each a discrete entity, arranged to convey the idea
of motion.
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