The Discrete Cosine Transform (DCT) is a method of reformating data which helps separate an image into spectral sub-bands of differing importance. The DCT is similar to the Discrete Fourier Transform (DFT) in that it transforms a signal or image from the spatial domain to the frequency domain. However, the DCT does a better job of concentrating energy into lower order coefficients the DFT for image data.

This is one part in several steps to generating a JPEG or MPEG compressed file.