Discrete cosine transform library in Java

Question

Is there a DCT library in Java which computes DCT in logarithmic time? I read that DCT can be computed with FFT algorithms, so there should also be a logarithmic time algorithm for dct.

Answer 1

You can compute a DCT by mirroring the data to double its length and doing an FFT on that double length vector.

Only the cosine terms of an FFT will be non-zero (except for numerical/rounding noise) for mirror symmetric (an even function about the center of the window) data.