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webp-lossless-bitstream-spec: add amendment note

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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
This commit is contained in:
James Zern 2022-11-21 11:24:16 -08:00
parent 607611cd86
commit 0ceeeab987
1 changed files with 6 additions and 2 deletions
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8
doc/webp-lossless-bitstream-spec.txt
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@ -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 \[AMENDED2\] were amended on 2022-05-13.
Paragraphs marked as \[AMENDED3\] were amended on 2022-11-21.
Abstract 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 decoded and the inverse color transform is applied on the ARGB values of
the pixels. As mentioned earlier, that inverse color transform is just the pixels. As mentioned earlier, that inverse color transform is just
adding `ColorTransformElement` values to the red and blue adding `ColorTransformElement` values to the red and blue
channels. channels. \[AMENDED3\]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
void InverseTransform(uint8 red, uint8 green, uint8 blue, 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 The decoder can convert a distance code `i` to a scan-line order distance
`dist` as follows: `dist` as follows:
\[AMENDED3\]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(xi, yi) = distance_map[i - 1] (xi, yi) = distance_map[i - 1]
dist = xi + yi * xsize 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); 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 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 lengths, `code_length_code_lengths`, first have to be read. The rest of those