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Is DCT a FFT?
DCT (Discrete Cosine Transform) is actually a cut-down version of the FFT: Only the real part of FFT. DCT MUCH more commonly used.
Is DCT better than FFT?
Discrete Cosine Transform (DCT) and Fast Fourier Transform (FFT). The result shows that DCT is better technique than FFT; however the compression results are same as that of 30% compression to 5% compression reflecting not significant change in visual results excepting the file size varying to small fraction.
What is the advantage of DFT over DCT on images?
> DCT is preferred over DFT in image compression algorithms like JPEG > because DCT is a real transform which results in a single real number per > data point. In contrast, a DFT results in a complex number (real and > imaginary parts) which requires double the memory for storage.
Which is correct, a DCT or a FFT?
My answer is generic regarding DCT/FFT. John’s idea is correct, but he is two-off regarding repeating the vector and has to compensate it by tweaking the coefficients (the e^ (pi * i / 2 / N) factor). With the right extension of the original vector, the FFT produces directly correct results (*). To quote from Wikipedia:
Is there a fast DCT in STATS package?
There appears to be no fast dct, but there is an fft (fast fourier transform) in the stats package, so here is how you could go about getting the fast dct using fft. Use this at your own risk. I haven’t done any serious checking of it.
Is the DCT-I the same as the DFT?
” The DCT-I is exactly equivalent (up to an overall scale factor of 2), to a DFT of 2N-2 real numbers with even symmetry. For example, a DCT-I of N=5 real numbers abcde is exactly equivalent to a DFT of eight real numbers abcdedcb (even symmetry), divided by two.
How to perform a * fast * DCT in R?
So if N is 2^K it is like doing a K different slow dct transforms on a vector of length two, so its really fast. If N is prime (worst case scenario) then there is no speed up at all. The greatest speedup is on vectors that are a power of two in length. Note: The R code above looks incredibly unfriendly, so let me say what is going on.