HEVC Entropy decoding Code Analysis-code decoding process (2)

Although the entropy decoding process is not very complex, it is annoying to have too many documents and functions involved, so a little bit of tidying up

Entropy decoding generally, it is necessary to initialize the context mode in the first place.

In HEVC

Because it is a class structure, in the declaration of the object, the basic completion of the general initialization work, the following detailed introduction:

Contains all the context patterns in the class Tdecsbac, but there are two corresponding structures in HM

Contextmodel         M_contextmodels[max_num_ctx_mod];//< altogether 512 elements of the  Int                  m_numcontextmodels;  Contextmodel3dbuffer M_ccusplitflagscmodel;  Contextmodel3dbuffer M_ccuskipflagscmodel;  Contextmodel3dbuffer M_ccumergeflagextscmodel;  Contextmodel3dbuffer M_ccumergeidxextscmodel;  Contextmodel3dbuffer M_ccupartsizescmodel;  Contextmodel3dbuffer M_ccupredmodescmodel;  Contextmodel3dbuffer M_ccuintrapredscmodel;

Contextmodel M_contextmodels[max_num_ctx_mod]; HEVC has 512 context modes altogether

Then m_numcontextmodels this class member variable to record how many context patterns each syntax element has

The Contextmodel3dbuffer type corresponds to the context pattern of each syntax element

Two more important variables in the M_numcontextmodels

UChar         m_ucstate;        < current slice in the corresponding state stateuint          m_binscoded;      < current number of bin, specific not very clear, follow-up continue to explain

Contextmodel3dbuffer

contextmodel* M_contextmodel; < array of context models  const UINT    M_sizex;        < X size of 3D buffer  const UINT    m_sizexy;       < X times Y size of 3D buffer  const UINT    m_sizexyz;      < total size of 3D buffer

There are 512 context modes, in each 3D mode, Contextmodel points to the pattern in 512, and three size variables are corresponding to how many patterns are in a syntax element,

Then the corresponding Contextmodel is obtained by the specific offset.

Initialization

Initialize the object when it is created

<span style= "COLOR: #ff0000;" >ContextModel3DBuffer::ContextModel3DBuffer</span> (UINT uisizez, uint uisizey, uint Uisizex, Contextmodel *   Baseptr, Int &count): M_sizex (Uisizex), m_sizexy (Uisizex * Uisizey), m_sizexyz (Uisizex * Uisizey * UiSizeZ) {  Allocate 3D buffer M_contextmodel = baseptr; Count + = m_sizexyz;} 

<span style= "color: #ff0000;" >tdecsbac::tdecsbac () </span>//new structure Here:m_pcbitstream (0), M_pctdecbini                      F (NULL), M_numcontextmodels (0), M_ccusplitflagscmodel (1, 1, num_split_flag_ctx, M_contextmodels + m_numcontext Models, M_numcontextmodels), M_ccuskipflagscmodel (1, 1, NUM_SKIP_                   Flag_ctx, M_contextmodels + m_numcontextmodels, m_numcontextmodels), M_ccumergeflagextscmodel (1, 1, num_merge_flag_ext_ctx, M_contextmodels + M_NUMCONTEXTMO Dels, M_numcontextmodels), M_ccumergeidxextscmodel (1, 1, num_merge_i        Dx_ext_ctx, M_contextmodels + m_numcontextmodels, m_numcontextmodels), M_ccupartsizescmodel               (1, 1, num_part_size_ctx, M_contextmodels + m_numcont Extmodels, M_numcontextmodels), M_ccupredmodescmodel (1, 1, NUM_PR                      Ed_mode_ctx, M_contextmodels + m_numcontextmodels, m_numcontextmodels), M_ccuintrapredscmodel (1, 1, num_adi_ctx, M_contextmodels + M_numcontex TModels, M_numcontextmodels), M_ccuchromapredscmodel (1, 1, Num_chro Ma_pred_ctx, M_contextmodels + m_numcontextmodels, m_numcontextmodels)

Complete the size of the context pattern contained in the corresponding Contextmodel and each syntax element in the Contextmodel3dbuffer pattern

The next initialization is initialized at the beginning of a slice, where the initialization is primarily the initial dissolve code environment

Mainly includes information such as range,mps in arithmetic coding.

Function entry:

Void Tdecslice: M in:d ecompressslice (tcominputbitstream** ppcsubstreams, tcompic* pcpic, tdecsbac* pcSbacDecoder)  _pcentropydecoder->setentropydecoder (Pcsbacdecoder  );  < polymorphic information is encoded in Cabac  m_pcentropydecoder->setbitstream      (ppcsubstreams[0]),//< sets the corresponding bitstream information  m_ Pcentropydecoder->resetentropy      (pcslice);//< Initial dissolve code environment

In the function

<pre name= "code" class= "CPP" >void tdecsbac::resetentropy (tcomslice* pslice) {Slicetype Slicetype = pSlice->  Getslicetype ();  Int QP = PSLICE-&GT;GETSLICEQP ();  if (Pslice->getpps ()->getcabacinitpresentflag () && Pslice->getcabacinitflag ())//xt? {switch (slicetype) {case P_slice://Change initialization table to B_slice initialization slic      EType = B_slice;    Break      Case B_slice://Change initialization table to P_slice initialization slicetype = P_slice;    Break      Default://should not occur assert (0);    Break  }} m_ccusplitflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_split_flag);  M_ccuskipflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_skip_flag);  M_ccumergeflagextscmodel.initbuffer (Slicetype, QP, (uchar*) init_merge_flag_ext); M_ccumergeidxextscmodel.initbuffer (Slicetype, QP, (uchar*)Init_merge_idx_ext);  M_ccupartsizescmodel.initbuffer (Slicetype, QP, (uchar*) init_part_size);  M_ccupredmodescmodel.initbuffer (Slicetype, QP, (uchar*) init_pred_mode);  M_ccuintrapredscmodel.initbuffer (Slicetype, QP, (uchar*) init_intra_pred_mode);  M_ccuchromapredscmodel.initbuffer (Slicetype, QP, (uchar*) init_chroma_pred_mode);  M_ccuinterdirscmodel.initbuffer (Slicetype, QP, (uchar*) init_inter_dir);  M_ccumvdscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_MVD);  M_ccurefpicscmodel.initbuffer (Slicetype, QP, (uchar*) init_ref_pic);  M_ccudeltaqpscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_DQP);  M_ccuqtcbfscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_QT_CBF);  M_ccuqtrootcbfscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_QT_ROOT_CBF); M_ccusigcoeffgroupscmodel.initbuffer (Slicetype, QP, (uchar*) init_sig_cg_flag);  M_ccusigscmodel.initbuffer (Slicetype, QP, (uchar*) init_sig_flag);  M_ccuctxlastx.initbuffer (Slicetype, QP, (uchar*) init_last);  M_ccuctxlasty.initbuffer (Slicetype, QP, (uchar*) init_last);  M_ccuonescmodel.initbuffer (Slicetype, QP, (uchar*) init_one_flag);  M_ccuabsscmodel.initbuffer (Slicetype, QP, (uchar*) init_abs_flag);  M_cmvpidxscmodel.initbuffer (Slicetype, QP, (uchar*) init_mvp_idx);  M_csaomergescmodel.initbuffer (Slicetype, QP, (uchar*) init_sao_merge_flag);  M_csaotypeidxscmodel.initbuffer (Slicetype, QP, (uchar*) init_sao_type_idx);  M_ccutranssubdivflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_trans_subdiv_flag);  M_ctransformskipscmodel.initbuffer (Slicetype, QP, (uchar*) init_transformskip_flag); M_cutransquantbypassflagscmodel.iniTbuffer (Slicetype, QP, (uchar*) init_cu_transquant_bypass_flag);  M_explicitrdpcmflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_explicit_rdpcm_flag);  M_explicitrdpcmdirscmodel.initbuffer (Slicetype, QP, (uchar*) init_explicit_rdpcm_dir);  M_cintrabcpredflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_intrabc_pred_flag);  M_ccrosscomponentpredictionscmodel.initbuffer (Slicetype, QP, (uchar*) init_cross_component_prediction);  M_chromaqpadjflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_chroma_qp_adj_flag);  M_chromaqpadjidcscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_CHROMA_QP_ADJ_IDC);  M_ccucolourtransformflagscmodel.initbuffer (Slicetype, QP, (uchar*) Init_colour_trans);  M_cintrabcbvdscmodel.initbuffer (Slicetype, QP, (uchar*) INIT_INTRABC_BVD);  M_pltmodeflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_pltmode_flag);       M_spointscmodel.initbuffer               (Slicetype, QP, (uchar*) init_spoint);  M_ccopytoprunscmodel.initbuffer (Slicetype, QP, (uchar*) init_top_run);  M_crunscmodel.initbuffer (Slicetype, QP, (uchar*) init_run);  M_pltsharingmodeflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_plt_reuse_flag);  M_pltscanrotationmodeflagscmodel.initbuffer (Slicetype, QP, (uchar*) init_scan_rotation_flag); for (UInt statisticindex = 0; Statisticindex < rext__golomb_rice_adaptation_statistics_sets; statisticindex++) {m  _golombriceadaptationstatistics[statisticindex] = 0; } m_pctdecbinif->start ();}

Where the initialization of the Buffur

Void Contextmodel3dbuffer::initbuffer (Slicetype slicetype, Int qp, uchar* ctxmodel) {  Ctxmodel + = Slicetype * M_sizeX YZ;  for (Int n = 0; n < m_sizexyz; n++)  {    m_contextmodel[n].init (QP, ctxmodel[n]);    m_contextmodel[n].setbinscoded (0);}  }

The incoming Ctxmodel is a pre-known table that initializes the state and bin variables for each contextmodel through Init

Initializing the decoding environment in arithmetic decoding in the start () function

Tdecbincabac::start () {  assert (m_pctcombitstream->getnumbitsuntilbytealigned () = = 0); #if rext__decoder_ Debug_bit_statistics  Tcomcodingstatistics::updatecabacstat (stats__cabac_initialisation, 510, 0); #endif  M_uirange    = 510;  m_bitsneeded =-8;  M_uivalue    = (M_pctcombitstream->readbyte () << 8);  M_uivalue   |= m_pctcombitstream->readbyte ();}

HEVC Entropy decoding Code Analysis-code decoding process (2)