Typos and undefined variables in ACT related text

[vdrugeon]

1. Typo in semantics of sps_act_enabled_flag: "sps_act_enabled_flag specifies that whether adaptive colour transform is enabled. "

2. Typo in semantics of cu_act_enabled_flag: "cu_act_enabled_flag is equal to 0 specifies that the residuals of the current coding unit are coded in original colour space"

3. In 8.4.5.1 General decoding process for intra blocks, the last step (step 4) in the process uses the variable resSample as input: "the picture reconstruction process for a colour component as specified in clause 8.7.5 is invoked with the transform block location ( xTbComp, yTbComp ) set equal to ( xTb0 + nW * xPartIdx, yTb0 + nH * yPartIdx ), the transform block width nTbW, the transform block height nTbH set equal to nW and nH, the variable cIdx, the (nW)x(nH) array predSamples[ x ][ y ] with x = xPartPbIdx * nW..( xPartPbIdx +1 ) * nW − 1, y = 0..nH − 1, and the (nW)x(nH) array resSamples as inputs,". However, when controlPara is equal to 2, resSamples is not derived in this process anymore, so that this variable is undefined when it is used. At first sight, it seems that resSamples should be one of the inputs of this process when controlPara is equal to 2. However, I think that it would probably be editorially cleaner to remove the picture reconstruction process step for this process and apply it one level higher in the specification (i.e. in 8.4.1 General decoding process for coding units coded in intra prediction mode). It would remove the need to have a process that has inputs and outputs that depends on the value of cu_act_enabled_flag.

[yk]

I fixed the first two aspects (semantics of sps_act_enabled_flag and sps_act_enabled_flag) in JVET-P2001-vC/v12, but did not check item 3.

[xyxiu]

ACT text bugfix

[xyxiu]

It is confirmed that in section 8.4.5.1, when controlPara is equal to 2, the (nW)x(nH) residual array resSamples are undefined. But, it seems the solution of moving the whole reconstruction process (step 4 in section 8.4.5.1) needs more text changes to the current specification. Instead, it is suggested to add resSamples as one input of section 8.4.5.1 when controlPara is equal to 2. This also complies with the way of how ACT text is written in the HEVC.

The corresponding text changes are attached.

[bbross]

Thanks for providing the spec text and this is fixed in JVET-S2001-v9.