Encyclopedia > Transform coding

  Article Content

Transform coding

Transform coding is a method for data compression to compress signals like audio signals (1-D) or images (2-D). In transform coding, a frequency transform or other basis transformation is applied before entropy coding, and the inverse transformation is applied after decoding. This has the advantage that the resulting coefficients have a statistically significant distribution and can be modelled and compressed more easily.

This means: After the transform, some coefficients are predictably greater, others smaller. Thus, some coefficients can be neglected or quantized (lossy compression) and/or entropy encoded (lossless compression).

For instance, JPEG performs a discrete cosine transform on 8-by-8 pixel blocks (in some pictures the chrominance is subsampled, so is transformed in 16-by-16 blocks with 3/4 of the results discarded), then the coefficients are quantized depending on their frequencies.

See also:

All Wikipedia text is available under the terms of the GNU Free Documentation License

  Search Encyclopedia

Search over one million articles, find something about almost anything!
  Featured Article
Sanskrit language

... (I) in the second line is nominative. na caaham = "...and not I....", meaning "but I am not...". "teshv-" (in/at/by them) at the end of the second line is in ...

This page was created in 33.4 ms