Using only 3 instead of 5 modes for 64x64 reportedly does not change the bit rate (-0.004) ‒ the additional 2 modes seem useless.
Using 9 instead of 34 modes for 32x32 increases the bit rate slightly for HE (+0.13), and does not change for LC (-0.03). However, this is not uniform over classes; the gain by using more modes is mostly achieved in class E (0.4%).
Based on the results, the suggestion was made to use following number of modes: 4x4:17; 8x8&16x16:34; 32x32: 9; 64x64:3. After discussion, the recommendation is to keep 34 modes also in the 32x32 size, as it seems to be beneficial for some cases, the restriction would not have implications on necessary decoder complexity, and an encoder could exclude those modes anyway if they are undesirable.
Decision: Change HM/WD, in 64x64 use only 3 intra modes (DC, horizontal, vertical); intra prediction for other block sizes unchanged (17 directions for 4x4, 3 directions for 64x64, 34 directions for others).
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