Data Representation

Data Representation
Information today comes in different forms such as text, numbers, images, audio, andvideo.

• Text

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.
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.

• Images

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

• 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. In Chapters 4 and 5, we learn how to change sound or music to a digital or an
analog 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. Again we can
change video to a digital or an analog signal, as we will see in Chapters 4 and 5.