Intel® Integrated Performance Primitives Developer Guide and Reference

ID 790148
Date 11/07/2023
Public

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Document Table of Contents

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

Include Files

ippi.h

Domain Dependencies

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

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

Parameters

pSrc

Pointer to the source image ROI.

srcStep

Distance, in bytes, between the starting points of consecutive lines in the source image.

pDst

Pointer to the destination image ROI.

dstStep

Distance, in bytes, between the starting points of consecutive lines in the destination image.

pDCTSpec

Pointer to the previously initialized inverse DCT context structure.

pBuffer

Pointer to the external work buffer.

Description

This function operates with ROI (see Regions of Interest in Intel IPP) of the size that is specified by the ippiDCTInvInit function.

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.

Before using the inverse DCT functions, you need to compute the size of the required buffers and the external work buffer using the ippiDCTInvGetSize function.

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.