JVET-P0430 AHG17: High level syntax cleanup on the syntax elements of transform skip [Y.-J. Chang, V. Seregin, M. Coban, M. Karczewicz (Qualcomm)]

The proposal is summarized as follows:

• Replace ue(v) with u(2) for the binarization of the syntax element log2_transform_skip_max_size_minus2
• Infer sps_transform_skip_enabled_flag to be 0 when MinCbLog2SizeY is larger than 5. Add a requirement of conformance that log2_transform_skip_max_size_minus2 shall be larger than or equal to log2_min_luma_coding_block_size_minus2.

The ue(v) signalling was inherited from RExt syntax. There is no obvious benefit replacing it with fixed length code.The issues mentioned under 2 are not critical, as there will be no problem in block-level decoding, since a TS flag would never appear (unless it would an illegal bitstream).

The aspect of moving the signalling from PPS to SPS needs further study anyway (see the notes under JVET-P0486).