FFTInit

Initializes the context structure for the image FFT functions.

Syntax

IppStatus ippiFFTInit_R_32f (int orderX, int orderY, int flag, IppHintAlgorithm hint, IppiFFTSpec_R_32f* pFFTSpec, Ipp8u* pMemInit);

IppStatus ippiFFTInit_C_32fc (int orderX, int orderY, int flag, IppHintAlgorithm hint, IppiFFTSpec_C_32fc* pFFTSpec, Ipp8u* pMemInit);

Include Files

ippi.h

Domain Dependencies

Headers: ippcore.h, ippvm.h, ipps.h

Libraries: ippcore.lib, ippvm.lib, ipps.lib

Parameters

orderX, orderY	Order of the FFT in x- and y- directions, respectively.
flag	Flag to choose the option for results normalization.
hint	This parameter is deprecated. Set the value to ippAlgHintNone.
pFFTSpec	Pointer to the FFT context structure.
pMemInit	Pointer to the temporary work buffer.

Description

This function initializes the pFFTSpec context structure needed to compute the forward and inverse FFT of a two-dimensional image data.

Before calling this function, you need to allocate memory for the FFT context structure and temporary work buffer (if it is required). To compute the size of the FFT context structure and temporary work buffer, use the ippiFFTGetSize function.

The pMemInit parameter can be NULL only if the work buffer is not used. After initialization is done, you can free the temporary work buffer.

The ippiFFTFwd and ippiFFTInv functions called with the pointer to the initialized pFFTSpec structure, compute the fast Fourier transform with the following characteristics:

length N=2^orderX in x-direction by M=2^orderYin y-direction
results normalization mode as set by flag (see Table “Normalization Factors for Fourier Transform Results”)
computation algorithm indicated by hint.

The suffix after the function name indicates the type of the context structure to be initialized: ippiFFTInit_C is for the complex FFT context structure and ippiFFTInit_R is for the real FFT context structure.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when one of the specified pointers is `NULL`.
ippStsFftOrderErr	Indicates an error condition when the FFT order value is illegal.
ippStsFFTFlagErr	Indicates an error condition when the flag value is illegal.

Example

The code example below demonstrates how to use the ippiFFTGetSize and ippiFFTInit functions.

/// get sizes for required buffers
    ippiFFTGetSize_R_32f( orderX, orderY, IPP_FFT_DIV_INV_BY_N, ippAlgHintNone, &sizeSpec, &sizeInit, &sizeBuffer );

    /// allocate memory for required buffers
    pMemSpec = (IppiFFTSpec_R_32f*) ippMalloc ( sizeSpec );

    if ( sizeInit > 0 )
    {
        pMemInit = ippMalloc ( sizeInit );
    }

    if ( sizeBuffer > 0 )
    {
        pMemBuffer = ippMalloc ( sizeBuffer );
    }

    /// initialize FFT specification structure
    ippiFFTInit_R_32f( orderX, orderY, IPP_FFT_DIV_INV_BY_N, ippAlgHintNone, pMemSpec, pMemInit );

    /// free initialization buffer
    if ( sizeInit > 0 )
    {
        ippFree( pMemInit );
    }

    /// perform forward FFT to put source data to frequency domain
    ippiFFTFwd_RToPack_32f_C1R( pSrc, srcStep, pDst, dstStep, pMemSpec, pMemBuffer );

    /// ...

    /// free buffers
    if ( sizeBuffer > 0 )
    {
        ippFree( pMemBuffer );
    }

    ippFree( pMemSpec );