It has been suggested that this article or section be merged with DC offset. (Discuss)
When describing a periodic function in the frequency domain, the term DC coefficient or DC component refers to the mean value of the waveform (possibly scaled according to the norm of the corresponding basis function of the frequency analysis filter bank). The name comes from an analogy to an electrical system in which this coefficient is analogous to a DC voltage or current, whilst the coefficients representing various other frequencies are analogous to superimposed AC voltages or currents. Wikipedia does not have an article with this exact name. ... It has been suggested that this article or section be merged with DC coefficient. ... Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ... In statistics, mean has two related meanings: the average in ordinary English, which is more correctly called the arithmetic mean, to distinguish it from geometric mean or harmonic mean. ... Waveform quite literally means the shape and form of a signal, such as a wave moving across the surface of water, or the vibration of a plucked string. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... City lights viewed in a motion blurred exposure. ...
The term's use is extended to two dimensional transformations like the DCT used in JPEG. 2-D DCT compared to the DFT The discrete cosine transform (DCT) is a Fourier-related transform similar to the discrete Fourier transform (DFT), but using only real numbers. ... In computing, JPEG (pronounced JAY-peg) is a commonly used standard method of lossy compression for photographic images. ...
For example, the brightness (the DCcoefficient) or shading across the tile (the 3 lowest ACcoefficients) must be reproduced fairly accurately, whereas the texture (middle frequency ACcoefficients) can be represented less accurately and the very fine detail (highest frequency ACcoefficients) is often invisible to the casual observer of the image.
Since the DCcoefficients are usually highly correlated, this reduces the entropy of the DC data stream (within the class of images usually seen, in any pixel ordering).
Each coefficient is thus represented by a pair of codes in the data stream, the first being a Huffman code translateable to a 4 bit PCM code, and the second an n-bit PCM code, where n is specified by the first 4 bit PCM code.
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