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| author | James Zern <jzern@google.com> | 2022-11-17 15:11:43 -0800 |
|---|---|---|
| committer | James Zern <jzern@google.com> | 2022-11-17 18:06:31 -0800 |
| commit | 44741f9c587e006e5289666b1cc8e63d97652315 (patch) | |
| tree | 7427a3416fcdc4a9f9603813370875ff2d20c492 | |
| parent | fad0ece7edec90dbead3cfbe19f2bc9d77a410e2 (diff) | |
| download | libwebp-44741f9c587e006e5289666b1cc8e63d97652315.tar.gz | |
webp-lossless-bitstream-spec: fix dist mapping example
The distance code read from the bitstream is reduced by 1 before doing
the lookup. The prose describing the lookup was correct, the pseudocode
failed to subtract 1 and used x/y instead of xi/yi from the lookup.
Bug: webp:448
Change-Id: I152477b888c26a0473a35373d3d331fddd14237f
| -rw-r--r-- | doc/webp-lossless-bitstream-spec.txt | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/doc/webp-lossless-bitstream-spec.txt b/doc/webp-lossless-bitstream-spec.txt index ecdfca3c..14afb949 100644 --- a/doc/webp-lossless-bitstream-spec.txt +++ b/doc/webp-lossless-bitstream-spec.txt @@ -764,14 +764,14 @@ The mapping between distance code `i` and the neighboring pixel offset For example, distance code `1` indicates an offset of `(0, 1)` for the neighboring pixel, that is, the pixel above the current pixel (0 pixel difference in X-direction and 1 pixel difference in Y-direction). Similarly, -distance code `3` indicates left-top pixel. +distance code `3` indicates the left-top pixel. The decoder can convert a distance code `i` to a scan-line order distance `dist` as follows: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -(xi, yi) = distance_map[i] -dist = x + y * xsize +(xi, yi) = distance_map[i - 1] +dist = xi + yi * xsize if (dist < 1) { dist = 1 } |