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AV1 Bitstream & Decoding Process Specification
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Descriptions of CSP_VERTICAL and CSP_COLOCATED refer to "(0, 0) luma sample", which is not defined #310

Open wantehchang opened 4 years ago

wantehchang commented 4 years ago

What version / commit were you testing with? (git describe can produce this info.)

AV1 Bitstream & Decoding Process Specification Last modified: 2019-01-08 11:48 PT Version 1.0.0 with Errata 1

In Section 6.4.2. Color config semantics, the last table describes the chroma sample position name CSP_VERTICAL as:

Horizontally co-located with (0, 0) luma sample, vertical position in the middle between two luma samples

and describes CSP_COLOCATED as:

co-located with (0, 0) luma sample

The descriptions refer to "(0, 0) luma sample", but that term is not defined in the spec.

wantehchang commented 4 years ago

I suspect the context for these descriptions is four luma samples in two rows and two columns, with coordinates (0, 0), (0, 1), (1, 0), and (1, 1), like so:

  (0, 0)  (0, 1)

  (1, 0)  (1, 1)

But this context is not described in the AV1 spec.

xzhaao commented 3 years ago

One possible change:

CSP_VERTICAL: the position of the corresponding luma sample for a chroma sample is not shifted horizontally, but shifted by 0.5 luma sample vertically toward the bottom of picture. CSP_COLLOCATED: the position of the corresponding luma sample for a chroma sample is not shifted either horizontally or vertically.

xzhaao commented 3 years ago

In addition, it seems none of CSP_VERTICAL, CSP_COLOCATED, CSP_RESERVED has been referenced in the spec text, maybe we can remove these names for the chroma sample positions.