DCTInv

Applies an inverse discrete cosine transform to an image.

Syntax

IppStatus ippiDCTInv_<mod> (const Ipp32f* pSrc, int srcStep, Ipp32f* pDst, int dstStep, const IppiDCTInvSpec_32f* pDCTSpec, Ipp8u* pBuffer);

Supported values for mod :

32f_C1R

32f_C3R

32f_C4R

32f_AC4R

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.
pDCTSpec	Pointer to the previously initialized inverse DCT context structure.
pBuffer	Pointer to the external work buffer, can be NULL.

Description

The function ippiDCTInv is declared in the ippi.h file. It operates with ROI (see Regions of Interest in Intel IPP) of the size that is specified by the function ippiDCTInvInitAlloc.

This function performs an inverse DCT on each channel of the input image pSrc and writes the result into the corresponding channel of the output image buffer pDst. Note that the function flavor with AC4 descriptor does not process alpha channel. This function uses the previously initialized pDCTSpec 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 DCT. 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 ippiDCTInvGetBufSize. 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 pDCTSpec 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 pDCTSpec structure is passed.
ippStsMemAllocErr	Indicates an error condition if memory allocation fails.