Include Files

Domain Dependencies

Headers:

ippcore.h

,

ippvm.h

Libraries:

ippcore.lib

,

ippvm.lib

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)

is

pDst

[n]

and

y

(k)

is

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.