2-D discrete cosine transform

If you apply the DCT to real data, the result is also real. The DCT tends to concentrate information, making it useful for image compression applications.

To invert the DCT transformation, use

`idct2`

.

[1] Jain, Anil K., *Fundamentals of Digital Image
Processing,* Englewood Cliffs, NJ, Prentice Hall, 1989, pp.
150–153.

[2] Pennebaker, William B., and Joan L. Mitchell,
*JPEG: Still Image Data Compression Standard,* Van Nostrand
Reinhold, 1993.