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webp-lossless-bitstream-spec: refine pixel copy text

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in 6.2.3 Decoding Entropy-Coded Image Data.

The copying of distance code pixels cause some confusion during the
AUTH48 portion of the RFC review process.

Bug: webp:611
Change-Id: I78f547ae10c95f180355a4c93ec6d48acdc09141
This commit is contained in:
James Zern 2023-06-05 16:44:12 -07:00
parent 29c9f2d410
commit 8b55425a56
1 changed files with 2 additions and 2 deletions
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4
doc/webp-lossless-bitstream-spec.txt
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@ -1046,8 +1046,8 @@ The interpretation of S depends on its value:
1. Read extra bits for the distance from the bitstream.
1. Determine backward-reference distance D from the distance prefix code
and the extra bits read.
1. Copy the L pixels (in scan-line order) from the sequence of pixels
prior to them by D pixels.
1. Copy L pixels (in scan-line order) from the sequence of pixels starting
at the current position minus D pixels.
1. If S >= 256 + 24
1. Use S - (256 + 24) as the index into the color cache.
1. Get ARGB color from the color cache at that index.