Developer Reference

  • 2021
  • 01/25/2021
  • Public Content
Contents

DCTFwd

Applies a forward discrete cosine transform to an image.

Syntax

IppStatus ippiDCTFwd_<mod> (const Ipp32f*
pSrc
, int
srcStep
, Ipp32f*
pDst
, int
dstStep
, const IppiDCTFwdSpec_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 forward 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
ippiDFTInit
function.
This function performs a forward DCT on each channel of the source image
pSrc
and writes the result into the corresponding channel of the destination 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.
You can use this function 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 forward DCT functions, you need to compute the size of the required buffers and the external work buffer using the
ippiDCTFwdGetSize
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.

Example

The code example below demonstrates how to use the
ippiDCTFwdGetSize
,
ippiDCTFwdInit
, and
ippiDCTFwd
functions.
void DCT_example( void ) { Ipp32f Src[8*8] = { 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 }; Ipp32f Dst[8*8]; IppiSize roiSize = {8, 8}; int srcStep; int dstStep; int sizeSpec; int sizeInit; int sizeBuffer; IppiDCTFwdSpec_32f *pMemSpec; Ipp8u *pMemInit = 0; Ipp8u *pMemBuffer = 0; srcStep = dstStep = 8 * sizeof(Ipp32f); /// get sizes for required buffers ippiDCTFwdGetSize_32f( roiSize, &sizeSpec, &sizeInit, &sizeBuffer ); /// allocate memory for required buffers pMemSpec = (IppiDCTFwdSpec_32f*) ippMalloc ( sizeSpec ); if ( sizeInit > 0 ) { pMemInit = (Ipp8u*) ippMalloc ( sizeInit ); } if ( sizeBuffer > 0 ) { pMemBuffer = (Ipp8u*) ippMalloc ( sizeBuffer ); } /// initialize DCT specification structure ippiDCTFwdInit_32f( pMemSpec, roiSize, pMemInit ); /// free initialization buffer if ( sizeInit > 0 ) { ippFree( pMemInit ); } /// perform forward DCT ippiDCTFwd_32f_C1R( Src, srcStep, Dst, dstStep, pMemSpec, pMemBuffer ); /// ... /// free buffers if ( sizeBuffer > 0 ) { ippFree( pMemBuffer ); } ippFree( pMemSpec ); }
Result:
Dst -> 28.0 -18.2 0.0 -1.9 0.0 -0.57 0.0 -0.14 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.