DecodeCoeffsIntra

Decodes AC coefficients for intra coded block.

Syntax

IppStatus ippiDecodeCoeffsIntra_H263_1u16s(Ipp8u** ppBitStream , int* pBitOffset , Ipp16s* pCoef, int* pIndxLastNonZero, int advIntraFlag, int modQuantFlag, int scan);

Parameters

ppBitStream

Pointer to pointer to the current byte in the bitstream buffer. **ppBitStream is updated by the function.

pBitOffset

Pointer to the bit position in the byte pointed by **ppBitStream. Valid within the range 0 to 7. *pBitOffset is updated by the function.

pCoef

Pointer to the output coefficients. pCoef[0] is the DC coefficient.

pIndxLastNonZero

Pointer to the index of the last non-zero coefficient in the scanning order. If an error is detected while decoding a coefficient, the index of the last decoded coefficient is returned in *pIndxLastNonZero. If the block has no correctly decoded coefficients, *pIndxLastNonZero is set to -1 when in Advanced Intra Coding mode, and to 0 otherwise.

advIntraFlag

Flag equal to a non-zero value when Advanced Intra Coding mode is in use, equal to 0 otherwise.

modQuantFlag

Flag equal to a non-zero value when Modified Quantization mode is in use, equal to 0 otherwise.

scan

Type of the inverse scan, takes one of the following values:

IPPVC_SCAN_ZIGZAG,	indicating the classical zigzag scan,
IPPVC_SCAN_HORIZONTAL,	indicating the alternate-horizontal scan,
IPPVC_SCAN_VERTICAL ,	indicating the alternate-vertical scan,
IPPVC_SCAN_NONE ,	indicating that no inverse scan is to be performed.

See the corresponding enumerator in the introduction to the General Functions .

Description

The function ippiDecodeCoeffsIntra_H263_1u16s is declared in the ippvc.h header file. This function performs VLC decoding and, optionally, inverse scan of the AC coefficients for one intra coded block. Intra AC VLC decoding process is specified in [ITUH263], subclause 5.4.2, and is modified as specified in [ITUH263] Annex T, clause T.4, when Modified Quantization mode is in use. When in Advanced Intra Coding mode, VLC Table I.2 from [ITUH263] Annex I is used for all intra DC and intra AC coefficients, otherwise Table 16 [ITUH263] is used to decode AC coefficients (starting from pCoef [1]) only. If scan is not set to IPPVC_SCAN_NONE, the DCT coefficients, encoded in the bitstream in the classical zigzag, alternate-horizontal, or alternate-vertical scan order, are reordered in the function into the normal order, that is, the order in which the coefficients are arranged on DCT output. The three scan patterns are shown in [ITUH263], Figure14 and [ITUH263], Annex I, Figure I.2.

This function is used in the H.263 decoder included into Intel IPP Samples. See introduction to H.263.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error condition if at least one of the specified pointers is NULL.
ippStsBitOffsetErr	Indicates an error condition if *pBitOffset is out of the range [0, 7].
ippStsVLCErr	Indicates an error condition if an illegal code is detected through the VLC stream processing.