id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
776	Mismatch on getting the down-sampled neighbouring top luma samples in CCLM for 4:2:2	wangyang.cs		"In JVET-P2001-vE, when sps_chroma_vertical_collocated_flag is equal to 0, the down-sampled neighbouring top luma samples in CCLM for 4:2:2 format videos are derived as follows:

8.4.5.2.13	Specification of INTRA_LT_CCLM, INTRA_L_CCLM and INTRA_T_CCLM intra prediction mode
...
    -The one-dimensional filter coefficients array F1 and F2, and the 2-dimensional filter coefficients arrays F3 and F4 are specified as follows.
            F1[ 0 ] = 2, F1[ 1 ] = 1				(356)
            F2[ 0 ] = 1, F2[ 1 ] = 2, F2[ 2 ] = 1	(357)
            F3[ i ][ j ] = F4[ i ][ j ] = 0, with i = 0..2, j = 0..2	(358)
        -If both SubWidthC and SubHeightC are equal to 2, the following applies:
            F1[ 0 ] = 1, F1[ 1 ] = 1				(359)
            F3[ 0 ][ 1 ] = 1, F3[ 1 ][ 1 ] = 4, F3[ 2 ][ 1 ] = 1, F3[ 1 ][ 0 ] = 1, F3[ 1 ][ 2 ] = 1	(360)
            F4[ 0 ][ 1 ]  = 1, F4[ 1 ][ 1 ] = 2, F4[ 2 ][ 1 ] = 1	(361)
            F4[ 0 ][ 2 ] = 1,  F4[ 1 ][ 2 ] = 2, F4[ 2 ][ 2 ] = 1	(362)
        -Otherwise, the following applies:
            F3[ 1 ][ 1 ] = 8					(363)
            F4[ 0 ][ 1 ] = 2, F4[ 1 ][ 1 ] = 4, F4[ 2 ][ 1 ] = 2,	[[span(style=color: #FF0000, (364) )]]
…
        -Otherwise (sps_chroma_vertical_collocated_flag is equal to 0), the following applies:
            -If x is greater than 0, the following applies:
            -If bCTUboundary is equal to FALSE, the following applies:
             pSelDsY[ idx ] = ( F4[ 0 ][ 1 ] * pY[ SubWidthC x − 1 ][ −2 ] +
		F4[ 0 ][ 2 ] * pY[ SubWidthC * x − 1 ][ −1 ] +
		F4[ 1 ][ 1 ] * pY[ SubWidthC * x ][ −2 ] +	[[span(style=color: #FF0000, (388) )]]
		F4[ 1 ][ 2 ] * pY[ SubWidthC * x ][ −1] +
		F4[ 2 ][ 1 ] * pY[ SubWidthC * x + 1 ][ −2 ] +
		F4[ 2 ][ 2 ] * pY[ SubWidthC * x + 1 ][ −1 ] + 4 ) >> 3
            -Otherwise (bCTUboundary is equal to TRUE), the following applies:
pSelDsY[ idx ] = ( F2[ 0 ] * pY[ SubWidthC * x − 1 ][ −1 ] +
		F2[ 1 ] * pY[ SubWidthC * x ][ −1 ] +	(389)
		F2[ 2 ] * pY[ SubWidthC * x + 1][ −1 ] + 2 ) >> 2
        -Otherwise (x is equal to 0), the following applies:
            -If availTL is equal to TRUE and bCTUboundary is equal to FALSE, the following applies:
pSelDsY[ idx ] = ( F4[ 0 ][ 1 ] * pY[ −1 ][ −2 ] + F4[ 0 ][ 2 ] * pY[ −1 ][ −1 ] +
		F4[ 1 ][ 1 ] * pY[ 0 ][ −2 ] + F4[ 1 ][ 2 ] * pY[ 0 ][ −1 ] +		F4[ 2 ][ 1 ] * pY[ 1 ][ −2 ] + F4[ 2 ][ 2 ] * pY[ 1 ][ −1 ] + 4 ) >> 3
[[span(style=color: #FF0000, (390) )]]
…

The 2nd line above current block is utilized to get the down-sampled neighbouring top luma samples in (388) and (390).
However, the 1st line is utilized in VTM7.0.

In {{{void IntraPrediction::xGetLumaRecPixels()}}}
…
  switch (pu.chromaFormat)
  {
    case CHROMA_422: //overwrite filter coefficient values for 422
      c0_2tap = 1, c1_2tap = 0,                                                     offset_2tap = 0, shift_2tap = 0; //sum = 1
      c0_3tap = 2, c1_3tap = 1, c2_3tap = 1,                                        offset_3tap = 2, shift_3tap = 2; //sum = 4
      c0_5tap = 0, c1_5tap = 1, c2_5tap = 0, c3_5tap = 0, c4_5tap = 0,              offset_5tap = 0, shift_5tap = 0; //sum = 1
      [[span(style=color: #FF0000, c0_6tap = 2, c1_6tap = 1, c2_6tap = 1, c3_6tap = 0, c4_6tap = 0, c5_6tap = 0, offset_6tap = 2, shift_6tap = 2; //sum = 4 )]]
      break;
    …
  }
…
  if( bAboveAvaillable )
  {
…
    for (int i = 0; i < uiCWidth + addedAboveRight; i++)
    {
…
      else
      {
        piSrc = pRecSrc0 - iRecStride2;

        if ((i == 0 && !bLeftAvaillable) || (i == uiCWidth + addedAboveRight - 1 + logSubWidthC))
        {
          pDst[i] = (piSrc[mult * i] * c0_2tap + piSrc[mult * i + strOffset] * c1_2tap + offset_2tap) >> shift_2tap;
        }
       [[span(style=color: #FF0000, else )]]
       {
          pDst[i] = ((piSrc[mult * i]            * c0_6tap + piSrc[mult * i - 1]             * c1_6tap + piSrc[mult * i + 1]             * c2_6tap)
                  + (piSrc[mult * i + strOffset] * c3_6tap + piSrc[mult * i - 1 + strOffset] * c4_6tap + piSrc[mult * i + 1 + strOffset] * c5_6tap)
                  + offset_6tap)  >>  shift_6tap;
        }
      }
    }
  }


Suggested fix is to align getting the down-sampled neighbouring top luma samples for CCLM in spec with VTM.
The modified draft is described as follows:


8.4.5.2.13	Specification of INTRA_LT_CCLM, INTRA_L_CCLM and INTRA_T_CCLM intra prediction mode
...
    -The one-dimensional filter coefficients array F1 and F2, and the 2-dimensional filter coefficients arrays F3 and F4 are specified as follows.
            F1[ 0 ] = 2, F1[ 1 ] = 1				(356)
            F2[ 0 ] = 1, F2[ 1 ] = 2, F2[ 2 ] = 1	(357)
            F3[ i ][ j ] = F4[ i ][ j ] = 0, with i = 0..2, j = 0..2	(358)
        -If both SubWidthC and SubHeightC are equal to 2, the following applies:
            F1[ 0 ] = 1, F1[ 1 ] = 1				(359)
            F3[ 0 ][ 1 ] = 1, F3[ 1 ][ 1 ] = 4, F3[ 2 ][ 1 ] = 1, F3[ 1 ][ 0 ] = 1, F3[ 1 ][ 2 ] = 1	(360)
            F4[ 0 ][ 1 ]  = 1, F4[ 1 ][ 1 ] = 2, F4[ 2 ][ 1 ] = 1	(361)
            F4[ 0 ][ 2 ] = 1,  F4[ 1 ][ 2 ] = 2, F4[ 2 ][ 2 ] = 1	(362)
        -Otherwise, the following applies:
            F3[ 1 ][ 1 ] = 8					(363)
            F4[ 0 ][ 1 ] = 2, F4[ 1 ][ 1 ] = 4, F4[ 2 ][ 1 ] = 2,	(364)
…
        -Otherwise (sps_chroma_vertical_collocated_flag is equal to 0), the following applies:
            -If x is greater than 0, the following applies:
            -If bCTUboundary is equal to FALSE, the following applies:
             pSelDsY[ idx ] = ( F4[ 0 ][ 1 ] * pY[ SubWidthC x − 1 ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] +
		F4[ 0 ][ 2 ] * pY[ SubWidthC * x − 1 ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]] ] +
		F4[ 1 ][ 1 ] * pY[ SubWidthC * x ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] +	(388)
		F4[ 1 ][ 2 ] * pY[ SubWidthC * x ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]]] +
		F4[ 2 ][ 1 ] * pY[ SubWidthC * x + 1 ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] +
		F4[ 2 ][ 2 ] * pY[ SubWidthC * x + 1 ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]] ] + 4 ) >> 3
            -Otherwise (bCTUboundary is equal to TRUE), the following applies:
pSelDsY[ idx ] = ( F2[ 0 ] * pY[ SubWidthC * x − 1 ][ −1 ] +
		F2[ 1 ] * pY[ SubWidthC * x ][ −1 ] +	(389)
		F2[ 2 ] * pY[ SubWidthC * x + 1][ −1 ] + 2 ) >> 2
        -Otherwise (x is equal to 0), the following applies:
            -If availTL is equal to TRUE and bCTUboundary is equal to FALSE, the following applies:
pSelDsY[ idx ] = ( F4[ 0 ][ 1 ] * pY[ −1 ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] + F4[ 0 ][ 2 ] * pY[ −1 ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]] ] +
		F4[ 1 ][ 1 ] * pY[ 0 ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] + F4[ 1 ][ 2 ] * pY[ 0 ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]] ] +		F4[ 2 ][ 1 ] * pY[ 1 ][ −[[span(style=color: #FF0000,~~2~~)]][[span(style=color: #00FF00,1)]] ] + F4[ 2 ][ 2 ] * pY[ 1 ][ −[[span(style=color: #FF0000,~~1~~)]][[span(style=color: #00FF00,2)]] ] + 4 ) >> 3
(390) )
…"	defect	closed	minor		spec	VVC D7 vE	fixed	CCLM, 4:2:2	ksuehring bbross XiangLi fbossen jvet@… jvet@…