Developer Reference

  • 2021
  • 06/28/2021
  • Public Content
Contents

Fourier Transforms

Intel IPP functions that compute FFT and DFT can process both real and complex images. Function flavors operating on real data are distinguished by R suffix present in function-specific modifier of their full name, whereas complex flavors' names include C suffix (see Function Naming).
The results of computing the Fourier transform can be normalized by specifying the appropriate value of
flag
argument for context initialization. This parameter sets up a pair of matched normalization factors to be used in forward and inverse transforms as listed in the following table:
Normalization Factors for Fourier Transform Results
Value of
flag
Argument
Normalization Factors
Forward Transform
Inverse Transform
IPP_FFT_DIV_FWD_BY_N
1/MN
1
IPP_FFT_DIV_INV_BY_N
1
1/MN
IPP_FFT_DIV_BY_SQRTN
1/sqrt(MN)
1/sqrt(MN)
IPP_FFT_NODIV_BY_ANY
1
1
In this table,
N
and
M
denote the length of Fourier transform in the x- and y-directions, respectively (or, equivalently, the number of columns and rows in the 2D array being transformed).
For the FFT, these lengths must be integer powers of 2, that is
N=2
orderX
,
M=2
orderY
, where power exponents
are known as order of FFT.
For the DFT,
N
and
M
can take on arbitrary integer non-negative values.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.