Unused filter in CCLM

[lingli0]

In VVC Draft8 vE, down-sample F4 is defined when either SubWidthC or SubHeightC is equal to 2. However, F4 is only used when both SubWidthC and SubHeightC are equal to 2. It is suggested to remove equation 369. Note that, this aspect is also pointed out in JVET-R0471.

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– 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 ] = 0 (361)
F2[ 0 ] = 1, F2[ 1 ] = 2, F2[ 2 ] = 1 (362)
F3[ i ][ j ] = F4[ i ][ j ] = 0, with i = 0..2, j = 0..2 (363)
– If both SubWidthC and SubHeightC are equal to 2, the following applies:
F1[ 0 ] = 1, F1[ 1 ] = 1 (364)
F3[ 0 ][ 1 ] = 1, F3[ 1 ][ 1 ] = 4, F3[ 2 ][ 1 ] = 1, F3[ 1 ][ 0 ] = 1, F3[ 1 ][ 2 ] = 1 (365)
F4[ 0 ][ 1 ] = 1, F4[ 1 ][ 1 ] = 2, F4[ 2 ][ 1 ] = 1 (366)
F4[ 0 ][ 2 ] = 1, F4[ 1 ][ 2 ] = 2, F4[ 2 ][ 2 ] = 1 (367)
– Otherwise, the following applies:
F3[ 1 ][ 1 ] = 8 (368)
-F4[ 0 ][ 1 ] = 2, F4[ 1 ][ 1 ] = 4, F4[ 2 ][ 1 ] = 2, (369)

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[bbross]

Good catch, thanks!

This is fixed in vB of D9, ie. JVET-R2001-v11.