Opened 10 years ago

Closed 9 years ago

#297 closed defect (fixed)

Context increment for coeff_abs_level_greater1_flag does not match HM-5.1

Reported by: pieterkapsenberg Owned by: bbross
Priority: minor Milestone: D7
Component: Text Version: D6 (H1003) dG
Keywords: coeff_abs_level_greater1_flag context increment Cc: jct-vc@…, bbross, wjhan

Description

I have noticed what looks like a discrepancy between the draft spec and HM-5.1. It is regarding the context increment derivation of coeff_abs_level_greater1_flag.

The spec says the following:

  • If n is equal to 15 or all previous syntax elements coeff_abs_level_greater1_flag[pos] with pos greater than n are derived to be equal to 0 instead of being explicitly parsed, the following applies.
    • ....
    • When the subset i is not the first one to be processed in this subclause, the following applies.
      • The variable numGreater1 is set equal to the variable numGreater1 that has been derived during the last invocation of subclause 9.3.3.1.1.6 for the syntax element coeff_abs_level_greater2_flag for the subset i + 1.
      • When (numGreater1 >> 1) is greater than 0, ctxSet is incremented by one as follows. ctxSet = ctxSet + 1

In HM-5.1, the comparison above is done before the downshift (TDecSbac.cpp, line 1937):

UInt uiCtxSet = (iSubSet > 0 && eTType==TEXT_LUMA) ? 3 : 0;
if( uiNumOne > 0 )
{

uiCtxSet++;
if(eTType==TEXT_LUMA && uiNumOne > 3)
{

uiCtxSet++;

}

}


uiNumOne >>= 1;

I think this can be fixed in the working draft by simply removing the downshift in the comparison

Change History (5)

comment:1 Changed 10 years ago by DefaultCC Plugin

  • Cc bbross wjhan added

comment:2 Changed 10 years ago by pieterkapsenberg

  • Version changed from WD5 (G1103) d6 to WD5 (G1103) d9

comment:3 Changed 10 years ago by bbross

  • Version changed from WD5 (G1103) d9 to D6 (H1003) dG

Revise when both HM6 and D6 are available.

comment:4 Changed 9 years ago by bbross

  • Milestone set to D7

comment:5 Changed 9 years ago by bbross

  • Resolution set to fixed
  • Status changed from new to closed

Fixed in JCTVC-I1003_d9.

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  • Benjamin Bross(Owner, Subscriber, Participant)
  • jct-vc@…(Subscriber)
  • karl.sharman@…(Always)
  • Karsten Suehring(Always)
  • Pieter Kapsenberg(Reporter, Participant)
  • Woo-Jin Han(Subscriber)