Visible to Intel only — GUID: GUID-8B117A9D-5A04-429D-8923-EF9BC9B29F32
Visible to Intel only — GUID: GUID-8B117A9D-5A04-429D-8923-EF9BC9B29F32
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=2orderX in x-direction by M=2orderYin 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 );