Opened 12 years ago

Closed 12 years ago

#909 closed defect (fixed)

Confusion in whether coordinates are for luma or chroma samples

Reported by: peterderivaz Owned by: bbross
Priority: trivial Milestone:
Component: Text Version: D9 (K1003) v11
Keywords: Cc: bbross, wjhan, jct-vc@…

Description

There seems to be a general confusion as to whether sample locations for blocks with cIdx>0 is given in luma or chroma samples.

The syntax elements seem to consistently use locations in luma samples, but the semantics are less clear.

For example,
in 8.4.4.1 "General decoding process for intra blocks", split_transform_flag is accessed via split_transform_flag[ xB0 << 1 ][ yB0 << 1 ][ trafoDepth ], implying locations in chroma samples.

however, in 8.4.4.2.1 "General intra sample prediction", equations 8-26 and 8-27 compute what is called "the luma location" (based on the same xB0 values), and use PredMode[xBN][yBN], implying locations in luma samples

Change History (3)

comment:1 Changed 12 years ago by DefaultCC Plugin

  • Cc bbross wjhan jct-vc@… added

comment:2 Changed 12 years ago by bbross

First, I can confirm the observation, that syntax elements common for luma and chroma are stored in array which is accessed using luma locations.

Regarding the issue mentioned here, I suggest the following variable change in 8.4.4.2.1 "General intra sample prediction":

  • neighboring location (xBN,yBN) -> (xN, yN) and use it here: 
"Otherwise, the sample p[ x ][ y ] is marked as "available for intra prediction" and the sample at the location ( xN, yN ) is assigned to p[ x ][ y ]."

and introduce the following two new variables:

  • (xBY, yBY) as the current luma location
  • (xNY, yNY) as the neighbouring luma location and use them here: 
The availability derivation process for a block in z-scan order as specified in subclause 6.4.1 is invoked with the current luma location ( xCurr, yCurr ) set equal to ( xBY, yBY ) and the neighbouring luma location ( xNY, yNY ) as the input and the output is assigned to availableN.

and here:

CuPredMode[ xNY ][ yNY ] is not equal to MODE_INTRA and constrained_intra_pred_flag is equal to 1

comment:3 Changed 12 years ago by bbross

  • Resolution set to fixed
  • Status changed from new to closed

Fixed in JCTVC-L1003_v1.

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