1.1.2 Data Representation:
Information today comes in different forms such as text, numbers, images, audio, and video.
In data communications, text is represented as a bit pattern, a sequence of bits (Os or Is).
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.
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.
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 blackand- white dots (e.g., a chessboard), a I-bit pattern is enough to represent a
pixel. If an image is not made of pure white and pure black pixels, you can increase the size of
the bit pattern to include gray scale. For example, to show four levels of gray scale, you 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.