CosineTransform Class 
Namespace: Accord.Math
Name  Description  

DCT(Double) 
Forward 2D Discrete Cosine Transform.
 
DCT(Double) 
Forward Discrete Cosine Transform.
 
IDCT(Double) 
Inverse 2D Discrete Cosine Transform.
 
IDCT(Double) 
Inverse Discrete Cosine Transform.

A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies. DCTs are important to numerous applications in science and engineering, from lossy compression of audio (e.g. MP3) and images (e.g. JPEG) (where small highfrequency components can be discarded), to spectral methods for the numerical solution of partial differential equations.
The use of cosine rather than sine functions is critical in these applications: for compression, it turns out that cosine functions are much more efficient, whereas for differential equations the cosines express a particular choice of boundary conditions.
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