Typo in 8.7.1 on chroma QP derivation

[LiZhang]

– The variables qPCb, qPCr and qPCbCr are derived as follows:

qPiChroma = Clip3( −QpBdOffsetC, 63, QpY ) (8 935)
qPiCb = ChromaQpTable[ 0 ][ qPiChroma ] (8 936)
qPiCr = ChromaQpTable[ 1 ][ qPiChroma ] (8 937)
qPiCbCr = ChromaQpTable[ 2 ][ qPiChroma ] (8 938)

In above equations, the variables starting with 'qPi' should be replaced by 'qP'.

[bbross]

Good catch and thanks for reporting.

This will be fixed JVET-P2001-vC.

[delagrangep]

Not completely fixed in JVET-P2001-vC (qPiChroma leftovers):

  qPChroma = Clip3( −QpBdOffset, 63, QpY )              (8 923)
  qPCb = ChromaQpTable[ 0 ][ qPiChroma ]                (8 924)
  qPCr = ChromaQpTable[ 1 ][ qPiChroma ]                (8 925)
  qPCbCr = ChromaQpTable[ 2 ][ qPiChroma ]              (8 926)

I suggest renaming qPChroma/qPiChroma to just qPi or even i; that variable is local to (8-924..926), which could be grouped into a single equation, e.g.:

  qPCb = ChromaQpTable[ 0 ][ i ]
  qPCr = ChromaQpTable[ 1 ][ i ]
  qPCbCr = ChromaQpTable[ 2 ][ i ]                      (8 923)
  with i = Clip3( −QpBdOffset, 63, QpY )

Even simpler, since clipping QpY is useless (already forced to legal range by overflow in (8-921), we can just write:

  qPCb = ChromaQpTable[ 0 ][ QpY]                 (8 923)
  qPCr = ChromaQpTable[ 1 ][ QpY ]                (8 924)
  qPCbCr = ChromaQpTable[ 2 ][ QpY ]              (8 925)

[bbross]

Thanks, for now I went for the minimal change in just removing the i.
Will be fixed in JVET-P2001-vD