ReconstructDCTBlock

Decodes 8X8 non-intra block using table of Run-Level codes for standard MPEG1, rearranges and performs inverse quantization.

Syntax

IppStatus ippiReconstructDCTBlock_MPEG1_32s(Ipp32u** ppBitStream, int * pOffset, const Ipp32s* pDCSizeTable, const Ipp32s* pACTable, Ipp32s* pScanMatrix, int QP, Ipp16s* pQPMatrix, Ipp16s* pDstBlock, Ipp32s* pDstSize);

Parameters

ppBitStream	Double pointer to the current position in the bit stream.
pOffset	Pointer to the offset between the bit that ppBitStream points to and the start of the code.
pDCSizeTable	Pointer to the table containing codes for DC coefficient, that is, the first of the DCT coefficients.
pACTable	Pointer to the table containing Run-Level codes for all DCT coefficients except the first one.
pScanMatrix	Pointer to the matrix containing indices of elements in scanning sequence.
QP	Quantizer scale factor read from the bit stream.
pQPMatrix	Pointer to the weighting matrix imposed by standard or user-defined.
pDstBlock	Pointer to decoded elements.
pDstSize	Position of the last non-zero block coefficient in scanning sequence.

Description

This function is declared in the ippvc.h header file. The function ippiReconstructDCTBlock_MPEG1_32s is applied to predicted and bi-predicted blocks and processes all the DCT coefficients in block using the tables of Run-Level codes: pDCSizeTable for DC coefficient and pACTable for AC coefficients.

The function uses the tables derived with HuffmanRunLevelTableInitAlloc function.

The pointer pScanMatrix points to the scanning matrix described in MPEG standard. Figure "Scanning Matrix and Sequence" illustrates a simple matrix and a sequence. After decoding, data is rearranged from scanning sequence to linear sequence. Then inverse quantization is performed: each of the DCT coefficients is multiplied by a corresponding value from the weighting matrix pQPMatrix and by the quantizer scale factor, which are read from the bit stream.

The function decodes the block of 8x8 DCT coefficients. The result is sent to pDstBlock and *pDstSize is the position of the last non-zero coefficient. After decoding, the pointers to code in the bitstream are reset as shown in Figure "Getting One Code From Bitstream".

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when at least one input pointer is NULL.
ippStsH263VLCCodeErr	Indicates an error when decoding in accordance with H263 standard.