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.
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 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.