FFTInv

Applies an inverse FFT to complex source data and stores results in a destination image.

Syntax

Case 1: Not-in-place operation on integer data

IppStatus ippiFFTInv_PackToR_<mod>(const Ipp32s* pSrc, int srcStep, Ipp8u* pDst, int dstStep, const IppiFFTSpec_R_32s* pFFTSpec, int scaleFactor, Ipp8u* pBuffer);

Supported values for mod:

32s8u_C1RSfs

32s8u_C3RSfs

32s8u_C4RSfs

32s8u_AC4RSfs

Case 2: Not-in-place operation on floating-point data

IppStatus ippiFFTInv_PackToR_<mod>(const Ipp32f* pSrc, int srcStep, Ipp32f* pDst, int dstStep, const IppiFFTSpec_R_32f* pFFTSpec, Ipp8u* pBuffer);

Supported values for mod:

32f_C1R

32f_C3R

32f_C4R

32f_AC4R

Case 3: Not-in-place operation on complex data

IppStatus ippiFFTInv_CToC_32fc_C1R(const Ipp32fc* pSrc, int srcStep, Ipp32fc* pDst, int dstStep, const IppiFFTSpec_C_32fc* pFFTSpec, Ipp8u* pBuffer);

Case 4: In-place operation on floating-point data

IppStatus ippiFFTInv_PackToR_<mod>(Ipp32f* pSrcDst, int srcDstStep, const IppiFFTSpec_R_32f* pFFTSpec, Ipp8u* pBuffer);

Supported values for mod:

32f_C1IR

32f_C3IR

32f_C4IR

32f_AC4IR

Case 5: In-place operation on complex data

IppStatus ippiFFTInv_CToC_32fc_C1IR(Ipp32fc* pSrcDst, int srcDstStep, const IppiFFTSpec_C_32fc* pFFTSpec, Ipp8u* pBuffer);

Parameters

pSrc	Pointer to the source image ROI.
srcStep	Distance in bytes between starts of consecutive lines in the source image.
pDst	Pointer to the destination image ROI.
dstStep	Distance in bytes between starts of consecutive lines in the destination image.
pSrcDst	Pointer to the source and destination image ROI for the in-place operation.
srcDstStep	Distance in bytes between starts of consecutive lines in the source and destination image for the in-place operation.
pFFTSpec	Pointer to the previously initialized FFT context structure.
scaleFactor	Scale factor (see Integer Result Scaling).
pBuffer	Pointer to the external work buffer, can be NULL.

Description

The function ippiFFTInv is declared in the ippi.h file. It operates with ROI (see Regions of Interest in Intel IPP).

This function performs an inverse FFT on each channel of the source image pSrc (pSrcDst for in-place flavors) and writes the restored image data into the corresponding channel of the destination image buffer pDst ( pSrcDst for in-place flavors). The size of ROI is N x M, it is specified by the parameters orderX, orderY calling the function ippiFFTInitAlloc.

For function flavor ippiFFTInv_PackToR, the input buffer must contain data in RCPack2D format.

The inverse FFT functions use the previously initialized pFFTSpec context structure to set the mode of calculations and retrieve support data.

The function may be used with the external work buffer pBuffer to avoid memory allocation within the functions. Once the work buffer is allocated, it can be used for all following calls to the functions computing FFT. As internal allocation of memory is too expensive operation and depends on operating system and/or runtime libraries used - the use of an external buffer improves performance significantly, especially for the small size transforms.

The size of the external buffer must be previously computed by the function ippiFFTGetBufSize. If the external buffer is not specified (pBuffer is set to NULL), the function itself allocates the memory needed for operation.

Return Values

ippStsNoErr	Indicates no error. Any other value indicates an error or a warning.
ippStsNullPtrErr	Indicates an error condition if pSrc, pDst, or pFFTSpec pointer is `NULL`.
ippStsStepErr	Indicates an error condition if srcStep or dstStep value is zero or negative.
ippStsContextMatchErr	Indicates an error condition if a pointer to an invalid pFFTSpec structure is passed.
ippStsMemAllocErr	Indicates an error condition if memory allocation fails.