The discrete cosine transform (DC T) represents an image as a sum of

sinusoids of varying magnitudes and frequencies. The dct2 function

computes the two-dimensional discrete cosine transform (DC T) of an

image. The DC T has the property that, for a typical image, most of the

visually significant information about the image is concentrated in just a few

coefficients of the DC T. For this reason, the DC T is often used in image

compression applications. For example, the DC T is at the heart of the international

standard lossy image compression algorithm known as JPEG. (The name comes

from the working group that developed the standard: the Joint Photographic

Experts Group). In practice, the DC T is normally implemented using the same basic

efficiency techniques as in FFT algorithms