Opened 12 years ago

Last modified 11 years ago

#1137 closed technical change

8.6.2 Normalisation of transform skip coefficients for blocksizes > 4x4 — at Initial Version

Reported by: davidf Owned by:
Priority: minor Milestone: RExt D5
Component: RExt text Version: RExt D4 (N1005) v3
Keywords: Cc: davidf, joels@…, teruhikos@…

Description

During integration, there was a conflict between two like proposals that extended transform skip to all TU sizes (JCTVC-N0288 and JCTVC-N0167).

N0288 normalises transform skip coefficients (left shift) according to block size:

  r[x][y] = d[x][y] << 7

Becomes

  r[x][y] = d[x][y] << (2 + Log2(nTbS))

N0167 does not change this process.

The current text follows N0167.

Not performing the shift causes loss of coefficient precision equivalent to an increase of QP by 6*(Log2(nTbS)-2). Eg, for an 8x8 TU, the lossless QP for transform skip is QP=10.

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