Commit Graph

98 Commits

Author SHA1 Message Date
James Zern
e30a588456 webp-lossless-bitstream-spec: update variable names
This syncs the document with the draft RFC.

block_xsize -> transform_width
i -> distance_code
x/ysize -> image_width/height

Change-Id: Ief442c90157e82c518e8cb175a522c519b16ac69
2023-10-09 21:24:01 -07:00
James Zern
40afa9269b webp-lossless-bitstream-spec: simplify abstract
This syncs the document with the draft RFC.

Change-Id: Ie6e9c9a50527378cb1b24e2c130a0a09855fe96e
2023-10-06 11:46:24 -07:00
Vincent Rabaud
accd141da3 Update lossless spec for two simple codes.
Bug: webp:611
Change-Id: If628bb9332ebca6dd11b3561c3458e0f43ed54a3
2023-09-14 22:43:45 +02:00
James Zern
aac5c5d0df ReadHuffmanCode: rm redundant num code lengths check
4 bits are read ([0, 15]) with 4 added to the result. The check that the
result is not > NUM_CODE_LENGTH_CODES (19) is redundant. This makes the
check an assert for documentation purposes.

webp-lossless-bitstream-spec.txt is updated accordingly.

Bug: webp:611
Change-Id: Ie461017dc9de3da4cfe6856543d3dcf58f53a180
2023-08-14 18:07:17 -07:00
James Zern
a2de25f6b6 webp-lossless-bitstream-spec: normalize list item case
In Section 6.2 Details, use uppercase after a :. This is more consistent
with the rest of the doc.

Bug: webp:611
Change-Id: I7ac862c90fd8e5fe0bad0dd5e3515d3095a6dc9a
2023-08-14 17:38:06 -07:00
James Zern
68820f0e53 webp-lossless-bitstream-spec: normalize pixel ref
x, y -> (x, y)

Bug: webp:611
Change-Id: Ic25ae76a9978156e7cd67ad17432ee1a1e172641
2023-08-14 17:38:03 -07:00
James Zern
cdb31aa806 webp-lossless-bitstream-spec: add missing periods
in ordered list in "6.2. Details". This is more consistent with the rest
of the document.

Bug: webp:611
Change-Id: Ie467c771afd5813a30855b24c80cf92673a5281c
2023-08-14 17:37:57 -07:00
James Zern
0535a8cf88 webp-lossless-bitstream-spec: fix grammar
...in same row... -> in the same row

Bug: webp:611
Change-Id: I837ab571084b206cc1a57c534c05cdcd0dfff0fa
2023-08-14 17:37:39 -07:00
James Zern
b6c4ce2635 normalize numbered list item format
from edits made during the RFC AUTH48 process

Change-Id: I82a5d78c0ea611e71927ffb13aa78ccdddfd6dd0
2023-08-09 13:51:38 -07:00
James Zern
dd88d2ff3e webp-lossless-bitstream-spec: color_cache -> color cache
The text is referring to the color cache, not a variable.

Bug: webp:611
Change-Id: Ife7e8246817ea0831993702bc050ed79998a0ee4
2023-07-27 12:41:04 -07:00
James Zern
67a7cc2b07 webp-lossless-bitstream-spec: fix code blocks
+ change "> 19" to "greater than 19" as it's referred to in prose

Bug: webp:611
Change-Id: I644d7d39f9c4a19050ff0256114873057aee95ef
2023-07-26 09:42:00 -07:00
James Zern
cd436142f6 webp-lossless-bitstream-spec: block -> chunk
when referring to the RIFF chunk size; this is more consistent with
other documentation.

Bug: webp:611
Change-Id: Icf05491ee79f5c48fab0b4935da397b4e4e45a71
2023-07-25 22:10:06 -07:00
James Zern
3cb66f64b0 webp-lossless-bitstream-spec: add some missing commas
The serial comma change is based on the Chicago Manual of Style
(CMOS), 17th edition.

Bug: webp:611
Change-Id: Ic02e6652662608414c16e0fead2912781a47633d
2023-07-25 22:09:59 -07:00
James Zern
56471a53cf webp-lossless-bitstream-spec: normalize item text in 5.1
Makes references to earlier sections consistent. Based on RFC editor
update.

Bug: webp:611
Change-Id: I63b1125810a3d8afa957d392e98c68a632749d76
2023-07-25 22:08:51 -07:00
James Zern
e94b36d66d webp-lossless-bitstream-spec: relocate details from 5.1
Move the details given for meta prefix codes and the transforms from
"5.1. Roles of Image Data" to their corresponding sections.

Bug: webp:611
Change-Id: I750a3f45956d0a3928a22113180a2590ac1a36db
2023-07-21 15:50:38 -07:00
James Zern
84628e5611 webp-lossless-bitstream-spec: clarify image width changes
After processing the Color Indexing Transform the image width is
subsampled by the transform's width_bits.

Bug: webp:611
Change-Id: If8d2d47dbe05e5c8085fb3fb4c1b63552be9028b
2023-07-20 17:54:20 -07:00
James Zern
982c177c8a webp-lossless-bitstream-spec: fix struct member refs
remove trailing '_' to match the definition of ColorTransformElement

Bug: webp:611
Change-Id: I741213b389fc88473c72c64090a4733f51d87925
2023-07-14 15:13:27 -07:00
James Zern
56cf562570 webp-lossless-bitstream-spec: use RFC 7405 for ABNF
This allows for case sensitive literals.

Bug: webp:611
Change-Id: I5258c67ab12c48593d433449328fd85d461a05d2
2023-07-14 15:13:27 -07:00
James Zern
6c6b3fd317 webp-lossless-bitstream-spec,cosmetics: delete blank lines
This normalizes the spacing between sections and quiets some lint
warnings.

Bug: webp:611
Change-Id: Ic36eb08d55a566def74f746e2ec225c67ff8aecf
2023-07-14 15:12:35 -07:00
James Zern
e4fc2f78c7 webp-lossless-bitstream-spec: add validity note for max_symbol
Bug: webp:611
Change-Id: Id56ca4fd0ad3cfc17c9c971281ccfb8ce7eaa2f4
2023-07-07 15:54:34 -07:00
James Zern
71916726b6 webp-lossless-bitstream-spec: fix max_symbol definition
If ReadBits(0) == 0, the value of max_symbol is set to the alphabet size
for each symbol type.

See vp8l_dec.c, ReadHuffmanCode(), which passes alphabet_size to
ReadHuffmanCodeLengths() as num_symbols, and ReadHuffmanCodeLengths()
then sets max_symbol to that.

Bug: webp:611
Change-Id: I662bd1d7f372e7f2e9c71cc86f87aefd02f36647
2023-07-07 15:54:34 -07:00
James Zern
4298e9765c webp-lossless-bitstream-spec: add PredictorTransformOutput
Describe the addition of the residual value to the predicted value.

Bug: webp:611
Change-Id: Id0300937eeebbafec3b2cd15376c56418c98a3bf
2023-06-26 12:51:36 -07:00
James Zern
cd7e02bece webp-lossless-bitstream-spec: fix RIFF-header ABNF
0x2f is a part of the image header, not RIFF header

Bug: webp:611
Change-Id: I5dba5ccfebeb25586723a1f3e00eebc317806928
2023-06-26 12:51:36 -07:00
James Zern
6c3845f9e0 webp-lossless-bitstream-spec: split LZ77 Backward Ref section
Make Distance Mapping its section for ease of reference.

Bug: webp:611
Change-Id: I57bb68e0fcf4d23ce0013f327adce93c6377be3a
2023-06-26 12:51:36 -07:00
James Zern
7f1b6799db webp-lossless-bitstream-spec: split Meta Prefix Codes section
Make Entropy Image and Interpretation of Meta Prefix Codes their own
section for ease of reference.

Bug: webp:611
Change-Id: I2dba7b4efd02d8bb250810ebff42ac1687262804
2023-06-26 12:51:36 -07:00
James Zern
7b634d8f0c webp-lossless-bitstream-spec: note transform order
transforms are applied in reverse bitstream order.

Bug: webp:611
Change-Id: I172aca36bbd5c3358a71b0acb49c5704ceee63d7
2023-06-26 12:51:36 -07:00
James Zern
6d6d4915ce webp-lossless-bitstream-spec: update transformations text
follow up to:
29c9f2d4 webp-lossless-bitstream-spec: minor wording updates

Universally use 'transform' over 'transformation'. The doc generally
uses 'transform' to talk about the individual transforms themselves as
well as their related data.

Bug: webp:611
Change-Id: I097701873bbc440bd399ab5440a914a14f7c62f6
2023-06-26 12:50:39 -07:00
James Zern
08d60d6006 webp-lossless-bitstream-spec: split code length section
Make Simple / Normal Code Length Code their own section for ease of
reference.

Bug: webp:611
Change-Id: I1e6ed50d98f9258cacb163d2059716b5356e8b6f
2023-06-21 19:20:12 -07:00
James Zern
7a12afcc54 webp-lossless-bitstream-spec: rm unused anchor
The last use of #decoding-the-code-lengths was removed in:
86f94ee0 Update lossless spec with Huffman codes.

Also remove the redundant section header associated with it.

Bug: webp:611
Change-Id: I7f6bb1a1b75255324f185f4591313d9e6d49d1e9
2023-06-21 19:16:39 -07:00
James Zern
14a9dbfba0 webp-lossless-bitstream-spec: refine single node text
Remove the ambiguous 'should' which in other contexts might result in
questions as to whether it is a SHOULD or a MUST.

Change-Id: I9b396187ebde5ea5a0dbaf42daee6acf541258cd
2023-06-20 19:30:20 -07:00
James Zern
03a7a04892 webp-lossless-bitstream-spec: rm redundant statement
Within the 'Entropy image' subsection, its clear this is what is being
described in the following paragraphs. Remove 'as described below' from
the first sentence.

Bug: webp:611
Change-Id: I365d69c8f6963cd826849ebdd96e46206d38b55d
2023-06-08 11:22:10 -07:00
James Zern
c437c7aace webp-lossless-bitstream-spec: mv up prefix code group def
Move this to the top-level of the "Details" section as prefix codes are
discussed in both "Decoding and Building the Prefix Codes" and "Decoding
of Meta Prefix Codes"

Bug: webp:611
Change-Id: Ide2dfedf081d6c94122ac16ecded968ed760f90c
2023-06-08 11:22:10 -07:00
James Zern
e4f17a31a7 webp-lossless-bitstream-spec: fix section reference
in the Transformations section describing decoding of the transform
data followed by the image data. The section numbers were adjusted by 1
in:
337cf69f webp-lossless-bitstream-spec: mv Nomenclature after Intro

Bug: webp:611
Change-Id: I4eede0d068fabdef51a140a0268436ab6629e8bb
2023-06-08 11:22:10 -07:00
James Zern
e2ecd5e937 webp-lossless-bitstream-spec: clarify ABNF syntax
Give some examples of repetition and binary value notation to limit the
need to follow the ABNF reference.

Bug: webp:611
Change-Id: I5b5a7632f011e1523b4a528653fe3630afba3e3e
2023-06-08 11:22:10 -07:00
James Zern
8b55425a56 webp-lossless-bitstream-spec: refine pixel copy text
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
2023-06-08 11:22:10 -07:00
James Zern
29c9f2d410 webp-lossless-bitstream-spec: minor wording updates
Mostly grammatical and addition/subtraction of commas from the AUTH48
portion of the RFC review process.

The serial comma changes are based on the Chicago Manual of Style
(CMOS), 17th edition.

Bug: webp:611
Change-Id: I5ae2d1cc0196009dbf3a4c2195cc73c2ef809b49
2023-06-08 11:21:55 -07:00
James Zern
c369c4bf0b doc/webp-lossless-bitstream-spec: improve link text
Reference the section by number, rather than 'this section'. Fixes a
lint warning:

Style notice: Write unique, descriptive link text that makes sense
without the surrounding text. Don't use phrases such as this document,
this article, or click here.
https://developers.google.com/style/link-text?hl=en#write-link-text

Change-Id: Iab33e4980528dddb5eed4404d25a4a746705131a
2023-05-26 15:48:28 -07:00
James Zern
9f38b71e01 doc/webp-lossless-bitstream-spec: prefer present tense
https://developers.google.com/style/tense

Change-Id: I1151ad0f585afd388920e6910a30aca4c2d0cc32
2023-05-26 15:48:17 -07:00
James Zern
4967e7cd78 doc/webp-lossless-bitstream-spec: avoid i.e. & e.g.
Using 'that is' or 'for example' is recommended:
https://developers.google.com/style/abbreviations#dont-use

Change-Id: I5d0dad2ee7ae5ebaf73661d5d79a4a2f1dc1802a
2023-05-26 15:48:09 -07:00
Jyrki Alakuijala
428588ef90 clarify single leaf node trees and use of canonical prefix coding
remove AMENDED-notes (the last functional spec change to match with the
implementation is from 2014, other amendments are clarifications)

Bug: webp:581
Change-Id: Ic47739be0fd5a975fd734d6813567ca615304f1d
2023-05-25 17:25:48 -07:00
James Zern
17e0ef1da5 webp-lossless-bitstream-spec: remove use of 'dynamics'
when bit width or precision are meant.

Change-Id: I89c2279e99b02c3e8a3bf39860364d2ce6d909c8
2023-05-12 15:10:30 -07:00
James Zern
84d04c4845 webp-lossless-bitstream-spec: add missing bits to ABNF
alpha-is-used and the version number were missing before 'image-stream'

spotted by thakis@

Change-Id: I7a4f1d2e0f0962bb1a79a0400c229738159d88a5
2023-04-13 12:13:34 -07:00
James Zern
4c3d7018c0 webp-lossless-bitstream-spec: condense normal-prefix-code
Have this match simple-prefix-code and redirect to "Normal Code Length
Code" as the added indirection to 'code-length-code' and the undefined
'encoded-code-lengths' doesn't add much.

spotted by thakis@

Change-Id: Icd6b64a47c4e0001e93271d9ae5585be4a6d5906
2023-04-10 17:22:55 -07:00
James Zern
a6a09b3296 webp-lossless-bitstream-spec: fix 2 code typos
- add missing '(' in DIV_ROUND_UP
- in 6.2.2, rename 'pos' variable reference to match definition
  ('position')

spotted by thakis@

Change-Id: Ida3ed281c2c753ebbb0e1eb3c4ed04dadc79ca24
2023-04-10 17:18:52 -07:00
James Zern
e5fe2cfc1b webp-lossless-bitstream-spec,cosmetics: reflow paragraphs
Change-Id: Ifd7472fe0678b45efc62faa66de8e8dc2e9931e3
2022-11-22 11:38:01 -08:00
James Zern
0ceeeab987 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
2022-11-22 11:38:01 -08:00
James Zern
f853685e13 lossless: SUBTRACT_GREEN -> SUBTRACT_GREEN_TRANSFORM
this makes the name of the TransformType enum value match the other
members

Bug: webp:448
Change-Id: I85b2f615f97b40fc6d544197cccfb7189dcf4fc0
2022-11-21 16:48:51 -08:00
James Zern
786497e48a webp-lossless-bitstream-spec: fix inv color txfm description
The prose describing the process was missed in:
44dd765d webp-lossless-bitstream-spec: fix ColorTransform impl

Bug: webp:448
Bug: webp:551
Change-Id: If5fb95103ffedeed113e3ad62510f3a19bfd280e
2022-11-21 16:48:51 -08:00
James Zern
c6ac672dbc webp-lossless-bitstream-spec: fix num_code_lengths check
in the 'Normal Code Length Code' description the number of valid code
lengths is 19, not 18.

Bug: webp:448
Bug: webp:551
Change-Id: Id929604e1d771cb09b2d0ac617e83f21077f21de
2022-11-21 16:48:51 -08:00
James Zern
b5700efb70 webp-lossless-bitstream-spec,cosmetics: grammar/capitalization
Bug: webp:448
Change-Id: I2d6cc66b45342716fdba7792c570510601432109
2022-11-21 16:48:41 -08:00