Developer Reference

  • 2020
  • 07/15/2020
  • 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

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804