DCTInv
DCTInv
Computes the inverse discrete cosine transform of a signal.
Syntax
Case 1: Not-in-place operation
IppStatus ippsDCTInv_32f(const Ipp32f*
pSrc
, Ipp32f*
pDst
, const IppsDCTInvSpec_32f*
pDCTSpec
, Ipp8u*
pBuffer
);
IppStatus ippsDCTInv_64f(const Ipp64f*
pSrc
, Ipp64f*
pDst
, const IppsDCTInvSpec_64f*
pDCTSpec
, Ipp8u*
pBuffer
);
Case 2: In-place operation
IppStatus ippsDCTInv_32f_I(Ipp32f*
pSrcDst
, const IppsDCTInvSpec_32f*
pDCTSpec
, Ipp8u*
pBuffer
);
IppStatus ippsDCTInv_64f_I(Ipp64f*
pSrcDst
, const IppsDCTInvSpec_64f*
pDCTSpec
, Ipp8u*
pBuffer
);
Include Files
ipps.h
Domain Dependencies
Headers:
ippcore.h
,
ippvm.h
Libraries:
ippcore.lib
,
ippvm.lib
Parameters
- pDCTSpec
- Pointer to the inverse DCT specification structure.
- pSrc
- Pointer to the source vector.
- pDst
- Pointer to the destination vector.
- pSrcDst
- Pointer to the source and destination vector for in-place operations.
- pBuffer
- Pointer to the external work buffer.
Description
This function computes the inverse discrete cosine transform (DCT) of the source signal
pSrc
(
pSrcDst
for in-place operations) in accordance with the specification structure
pDCTSpec
that must be initialized by calling
ippsDCTInvInit
beforehand. The result in stored in the
pDst
(
pSrcDst
for in-place operations).
If
len
is a power of 2, the functions use an efficient algorithm that is significantly faster than the direct computation of DCT. For other values of
len
, these functions use the direct formulas given below; however, the symmetry of the cosine function is taken into account, which allows to perform about half of the multiplication operations in the formulas.
In the following definition of DCT,
,
N
=
len
x
(n)
pDst
[n]
y
(k)
pSrc
[k]
The inverse DCT is defined by the formula:
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 this buffer must be computed previously using
ippsDCTInvGetSize
.
If the external buffer is not specified (
pBuffer
is set to
NULL
), then the function itself allocates the memory needed for operation.
Return Values
- ippStsNoErr
- Indicates no error.
- ippStsNullPtrErr
- Indicates an error if one of thepDCTSpec,pSrc,pDst,pSrcDstpointers isNULL.
- ippStsContextMatchErr
- Indicates an error when the specification identifierpDCTSpecis incorrect.
- ippStsMemAllocErr
- Indicates an error if memory allocation fails.