The discrete Fourier sine and cosine transforms (DST and DCT) can be used to decompose or represent a given digital signal (that is, discrete) in the form of a set of sums of sines and cosines. Four transform types are possible.

In the graphics, the initial signal is converted forward and back by the selected discrete Fourier transforms. For specific cases, either a cosine or a sine transform may be a better representation of the original signal than a combination of sine and cosine terms.