Hello,

I have two points concerning the candidate selection for intra prediction mode.

1. In 8.4.2 (derivation process for luma prediction mode), when candIntraPredModeA == candIntraPredModeB and candIntraPredModeA >= 2,

(8-20) reads candModeList[2] = 2 + ((candIntraPredModeA - 2 + 1) % 32)

so when candIntraPredModeA == 33, this formula gives

candModeList[2] = 2 + ((33 - 2 + 1) % 32) = 2 + (32 % 32) = 2

I think that in this case, we should use the mode 34 for candModeList[2] instead of 2 because it is the neighbouring mode of 33.

If this suggestion is adopted, the new formula for (8-20) will be :

candModeList[2] = 3 + ((candIntraPredModeA - 2) % 32)

2. Also in the same case candIntraPredModeA == candIntraPredModeB and candIntraPredModeA >= 2,

+ if candIntraPredModeA == 2, candModeList[1] and candModeList[2] are 3 and 33
+ if candIntraPredModeA == 34, candModeList[1] and candModeList[2] are 2 and 33

I am wondering in these two cases, instead of choosing the opposite direction (33 and 2 respectively), whether neighbouring modes (4 and 32) will be better. In other words,

+ if candIntraPredModeA == 2, candModeList[1] and candModeList[2] are 3 and 4
+ if candIntraPredModeA == 34, candModeList[1] and candModeList[2] are 32 and 33

Best regards,
Phuong Nguyen.