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| author | James Zern <jzern@google.com> | 2022-11-21 11:24:16 -0800 |
|---|---|---|
| committer | James Zern <jzern@google.com> | 2022-11-22 11:38:01 -0800 |
| commit | 0ceeeab987cba59ef7ee3369bdc167067094ddc2 (patch) | |
| tree | c9a293cc131db17f983c90e57ef459bc17a11876 | |
| parent | 607611cd86a5ac19c481de567f8e5d5328347c40 (diff) | |
| download | libwebp-0ceeeab987cba59ef7ee3369bdc167067094ddc2.tar.gz | |
webp-lossless-bitstream-spec: add amendment note
for fixes to the distance_map pseudo-code, the inverse color transform
description and the num_code_lengths check.
Bug: webp:448
Bug: webp:551
Change-Id: Id7e791b97704dd64bb9519657ce48b92cb457ae4
| -rw-r--r-- | doc/webp-lossless-bitstream-spec.txt | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/doc/webp-lossless-bitstream-spec.txt b/doc/webp-lossless-bitstream-spec.txt index 450bc050..fc7591f9 100644 --- a/doc/webp-lossless-bitstream-spec.txt +++ b/doc/webp-lossless-bitstream-spec.txt @@ -18,6 +18,8 @@ Paragraphs marked as \[AMENDED\] were amended on 2014-09-16. Paragraphs marked as \[AMENDED2\] were amended on 2022-05-13. +Paragraphs marked as \[AMENDED3\] were amended on 2022-11-21. + Abstract -------- @@ -465,7 +467,7 @@ During decoding, `ColorTransformElement` instances of the blocks are decoded and the inverse color transform is applied on the ARGB values of the pixels. As mentioned earlier, that inverse color transform is just adding `ColorTransformElement` values to the red and blue -channels. +channels. \[AMENDED3\] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ void InverseTransform(uint8 red, uint8 green, uint8 blue, @@ -771,6 +773,8 @@ Similarly, the 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: +\[AMENDED3\] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (xi, yi) = distance_map[i - 1] dist = xi + yi * xsize @@ -910,7 +914,7 @@ First, `num_code_lengths` specifies the number of code lengths. int num_code_lengths = 4 + ReadBits(4); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -If `num_code_lengths` is > 19, the bitstream is invalid. +If `num_code_lengths` is > 19, the bitstream is invalid. \[AMENDED3\] The code lengths are themselves encoded using prefix codes: lower level code lengths, `code_length_code_lengths`, first have to be read. The rest of those |