(x) ¶(x, n) ¶Compute the discrete cosine transform of x. If n is given, then x is padded or trimmed to length n before computing the transform. If x is a matrix, compute the transform along the columns of the the matrix. The transform is faster if x is real-valued and has even length.
The discrete cosine transform x can be defined as follows:
N-1
X[k] = w(k) sum x[n] cos (pi (2n+1) k / 2N ), k = 0, ..., N-1
n=0
with w(0) = sqrt(1/N) and w(k) = sqrt(2/N), k = 1, ..., N-1. There are other definitions with different scaling of X[k], but this form is common in image processing.
See also: idct, dct2, idct2, dctmtx.
Package: signal