Transform coding

Transform coding (English transform coding) is a method of data compression for signals such as audio signals ( 1D) or images ( 2D). Here, a frequency transform the actual data compression is usually preceded. This has the advantage that the resulting coefficients exhibit a statistically significant distribution and can therefore be better modeled and subsequently compressed.

In other words: After the transformation, some coefficients are predictably larger, others smaller. Therefore, one can neglect smaller coefficients ( lossy compression) and / or apply entropy coding ( lossless compression).

The majority of the common modern lossy compressed audio and video formats, such as the format family of MPEG ( MP3, MPEG -2, ... ) are based transform coding using the modified discrete cosine transform ( MDCT ), which is a form of fast Fourier transform ( FFT) represents. However, attempts are also made to work more with wavelet transforms, especially in the field of image processing.

• Data compression