Digital
The term is much more commonly used in digital media and in digital signal processing. The common JPEG image format is an example of a transform coding, one that examines small blocks of the image and "averages out" the color using a discrete cosine transform to form an image with far fewer colors in total. MPEG modifies this across frames in a motion image, further reducing the size compared to a series of JPEGs. A widely used transform in this regard is the Discrete Cosine Transform (DCT), developed by in 1974 by N. Ahmed, T. Natarajan and K. R. Rao; see Reference 1 in discrete cosine transform. The DCT is sometimes referred to as "DCT-II" in the context of a family of discrete cosine transforms; e.g., see discrete cosine transform. MPEG audio compression analyzes the transformed data according to a psychoacoustic model that describes the human ear's sensitivity to parts of the signal, similar to the TV model.
The basic process of digitizing an analog signal is a kind of transform coding that uses sampling in one or more domains as its transform.
Read more about this topic: Transform Coding