Programmer Guide/SPU Reference/DCTRANS

DCTRANS - discrete cosine transform

Usage:

DCTRANS x dir n

Inputs:

x	input vector
dir	direction: 'Forward' or 'Inverse'
n	the number of coefficients

Outputs:

y	vector containing result of transformation

Function:

Discrete Cosine Transform (DCT) - forward and inverse. The DCT is defined as follows:

for , for

The forward DCT is defined by the formula:

If dir is Forward:

if 0 < n < len(x)	only the first n coefficients are stored in the output
otherwise	len(x) coefficients are stored in the output

The definition of the inverse discrete cosine transform is:

If dir = Inverse:

if 0 < n < len(x)	only the first n coefficients of x are used for the
	inverse transformation (the others are set to 0);
	transformation and output length = len(x)
if n > len(x)	vector x is expanded with zeros to length n
	transformation and output length = n
otherwise	transformation and output length = len(x)