id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1026	Mismatch on Inverse JCCR between SW and Spec	tsukuba.takeshi		"In VTM-8.0, there is a clipping operation in inverse JCCR process as below:

template<int signedMode> void invTransformCbCr( PelBuf &resCb, PelBuf &resCr )
{
  Pel*  cb  = resCb.buf;
  Pel*  cr  = resCr.buf;
  for( SizeType y = 0; y < resCb.height; y++, cb += resCb.stride, cr += resCr.stride )
  {
    for( SizeType x = 0; x < resCb.width; x++ )
    {
      if      ( signedMode ==  1 )  { cr[x] =  cb[x] >> 1;  }
      else if ( signedMode == -1 )  { cr[x] = -cb[x] >> 1;  }
      else if ( signedMode ==  2 )  { cr[x] =  cb[x]; }
      else if ( signedMode == -2 )  { cr[x] = '''(cb[x] == -32768 && sizeof(Pel) == 2) ? 32767 : -cb[x]; }   // non-normative clipping to prevent 16-bit overflow'''
      else if ( signedMode ==  3 )  { cb[x] =  cr[x] >> 1; }
      else if ( signedMode == -3 )  { cb[x] = -cr[x] >> 1; }
    }
  }
}

On the other hand, the spec (JVET-Q2001vE) doesn't have such a clipping operation.

8.7.2	Scaling and transformation process
...

3.The residual samples resSamples[ x ][ y ] with x = 0..nTbW − 1, y = 0..nTbH − 1 are derived as follows:
–If cIdx is equal to codedCIdx, the following applies:
    resSamples[ x ][ y ] = res[ x ][ y ]                     (1151)
–Otherwise, if TuCResMode[ xTbY ][ yTbY ] is equal to 2, the following applies:
    resSamples[ x ][ y ] = cSign * res[ x ][ y ]             (1152)
–Otherwise, the following applies:
    resSamples[ x ][ y ] = ( cSign * res[ x ][ y ] ) >> 1    (1153)


Suggested fixes are 1) or 2):
-1) align SW to Spec, i.e. remove clipping operation.
-2) align Spec to SW, i.e. add clipping operation.
"	defect	closed	minor		VTM	VTM-8.0	invalid		ksuehring XiangLi fbossen jvet@…