Visible to Intel only — GUID: GUID-0AB9AE97-A9F3-4A8C-99E8-82C882CB4CCA
Visible to Intel only — GUID: GUID-0AB9AE97-A9F3-4A8C-99E8-82C882CB4CCA
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, orpDCTSpec 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