Discrete Cosine Transform  DCT Definition  The discrete cosine
transform (DCT) represents an image as a sum of sinusoids of
varying magnitudes and frequencies. The dct2 function computes
the two-dimensional discrete cosine transform (DCT) of an image.
The DCT 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 DCT. For this reason, the DCT
is often used in image compression applications. For example,
the DCT 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.)  The two-dimensional DCT of an
M-by-N matrix A is defined as follows.   The values Bpq are
called the DCT coefficients of A. (Note that matrix indices in
MATLAB® always start at 1 rather than 0; therefore, the MATLAB
matrix elements A(1,1) and B(1,1) correspond to the mathematical
quantities A00 and B00, r