ELEMENTS

TECHNICAL FIELD

The invention relates generally to video processing. In particular, the present invention relates to methods and apparatuses for bypass coding and reducing contexts in High Efficiency Video Coding (HEVC).

BACKGROUND

HEVC (High Efficiency Video Coding) is an advanced video coding system being developed under the Joint Collaborative Team on Video Coding (JCT-VC) group of video coding experts from ITU-T Study Group. In HEVC test model version 5.0 (HM-5.0), the syntax elements merge_flag, merge_idx, ref_idx_lc, predjype, and cu qp delta are coded with contexts in CAB AC. Merge flag that is equal to either 0 or 1 has only one bin and uses one context. The bin strings of merge idx, ref idx lc, and pred type are shown in Table 1 , Table 2 and Table 3 respectively. For merge idx, pred type and ref idx lc, one context is used for one bin. If the maximum value of ref idx lc is larger than 3, the additive bins share the same context as the bin with binldx equal to 2. The bin string of cu qp delta is specified by a process equivalent to the following pseudo-code. The value of cu qp delta is denoted as synVal. absV = Abs( synVal )

if( absV = = 0 ){

put( 0 ) ^■ binldx = 0

} else {

put( 1 ) ^■ binldx = 0

signV = ( synVal > 0 ) ? 0 : 1

put( signV )

cMax = 24 + ( QpBdOffsetY » 1 ) + signV cNum = absV - 1

absVGreaterThanlFlag = ( absV

put( absVGreaterThanlFlag )

if( absVGreaterThanlFlag ){

while( cNum— )

put( 1 ) binldx = 2

if( cMax > absV - 1 )

put( 0 )

}

}

The contexts used for the bin string are also given in the above pseudo-code. The first two bins of cu qp delta with binldx equal to 0 and 1 use two separate contexts for each bin, while other bins with binldx equal to or larger than 2 use one bin. When using contexts, additional memory and complexity are required at both encoder and decoder.

Table 1. Bin string of merge_idx in HM5.0

Table 2. Bin string of ref_idx_lc in HM5.0 Value Bin string

0 0

1 1 0

2 1 1 0

3 1 1 1 binldx 0 1 2

Table 3. Bin string of pred_type for inter blocks in HM5.0

SUMMARY

In light of the previously described problems, there exists a need for an apparatus and method, in which the number of contexts is reduced or the bypass coding without using contexts is applied to some syntax elements. BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating an exemplary method of reducing contexts for ref idx lc.

DETAILED DESCRIPTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

In the first embodiment, the syntax element merge flag is coded with bypass coding method. No context is required for that.

In the second embodiment, as for the syntax element merge idx, the bins with binldx equal to 1 , 2 and 3 share one context.

In the third embodiment, as for the syntax element merge idx, the bins with binldx equal to 2 and 3 share one context.

In the fourth embodiment, as for the syntax element merge idx, the bin with binldx equal to 3 is coded with bypass coding method. No context is required for that bin.

In the fifth embodiment, as for the syntax element merge idx, the bin with binldx equal to 2 is coded with bypass coding method. No context is required for that bin.

In the sixth embodiment, as for the syntax element merge idx, the bin with binldx equal to 1 is coded with bypass coding method. No context is required for that bin.

In the seventh embodiment, as for the syntax element merge idx, the bins with binldx equal to 1, 2 and 3 are coded with bypass coding method. No context is required for those bins.

In the eighth embodiment, as for the syntax element ref idx lc, the bins with binldx equal to 1 and 2 share one context, as shown in Fig. 1.

In the ninth embodiment, as for the syntax element ref idx lc, the bin with binldx equal to 2 is coded with bypass coding method. No context is required for those bins.

In the tenth embodiment, as for the syntax element ref idx lc, the bin with binldx equal to 1 is coded with bypass coding method. No context is required for those bins.

In the eleventh embodiment, as for the syntax element ref idx ld, the bins with binldx equal to 1 and 2 are coded with bypass coding method. No context is required for those bins.

In the twelfth embodiment, as for the syntax element pred type, the bin with binldx equal to 4 is coded with bypass coding method. No context is required for that bin.

In the thirteenth embodiment, as for the syntax element pred type, the bin with binldx equal to 3 is coded with bypass coding method. No context is required for that bin.

In the forteenth embodiment, as for the syntax element pred type, the bin with binldx equal to 2 is coded with bypass coding method. No context is required for that bin.

In the fifteenth embodiment, as for the syntax element pred type, the bins with binldx equal to 4, 3, and 2 are coded with bypass coding method, as shown in Fig. 1. No context is required for those bins.

In the sixteenth embodiment, as for the syntax element pred type, the bins with binldx equal to 4, 3, and 2 share one context.

In the seventeenth embodiment, as for the syntax element pred type, the bins with binldx equal to 4 and 3 share one context.

In the eighteenth embodiment, as for the syntax element pred type, the bins with binldx equal to 3 and 2 share one context.

In the nineteenth embodiment, as for the syntax element cu qp delta, the bins with binldx equal to or larger than 2 are coded with bypass coding method. No context is required for those bins.

In the twentieth embodiment, as for the syntax element cu qp delta, the bin with binldx equal to 1 is coded with bypass coding method. No context is required for that bin. In the twenty-first embodiment, as for the syntax element cu qp delta, the bin with binldx equal to 1 and the bins with binldx equal to or larger than 2 are coded with bypass coding method. No context is required for those bins.

In the twenty-second embodiment, as for the syntax element cu qp delta, the bin with binldx equal to 1 and the bins with binldx equal to or larger than 2 use one context.