Break the main README into into multiple pages in the doc/ directory,
except for the tests, swig and webp_js docs which are in the corresponding
directories.
The webp mux doc is merged into the API doc and the tools doc.
Change-Id: Ia407617dd88094f4662841d37947cfef80799914
- prefer Exif to EXIF when not referring to the chunk
- normalize use of code format for canvas / frame width & height
Change-Id: I7fc9e87baeb5d8e719274680ce621dcb078a985f
- prefer https
- metadataworkinggroup.org/com seem to be offline; the web archive link
was obtained from exiftool: https://exiftool.org/TagNames/MWG.html
- fix kramdown link, rubyforge has been gone a long time
- fix png/zlib links
Bug: webp:544
Bug: b/202302177
Change-Id: Id69de4553e7baf00393f12a2c1acb262443a1a93
to https://datatracker.ietf.org/doc/html/... the http tools.ietf.org
links redirect here sometimes, in other cases they 404.
Bug: webp:544
Change-Id: I900972070d6c5659c45a86a89e78b870f42fe5bc
unknown chunks as a group are well defined in the text
+ remove the Note about stable features as it matched the list given;
there are no WIP features for the format
Change-Id: I11a4de39f9d203b815879f0e9dea9c45b2ae6ff6
replace with more inclusive terms or remove the comment entirely if the
meaning was already clear.
Bug: webp:507
Change-Id: Ica3bbf751ebf79f6668df6e6209af770248ff4ca
the interpretation of a 0 duration depends on the implementation;
merging of multiple frames isn't guaranteed, some may enforce a minimum
duration.
BUG=webp:380
Change-Id: Idf592049d2092e4cc5cfb2e4c59ddbc91bd52f9c
partially normalize indent, vertical whitespace and capitalization with
the copy used on developers.google.com/speed/webp
Change-Id: I8044418eeb9eaf5bd5c799675c74f6f845d503d6
at the beginning of the loop there's an implicit clear of the entire
canvas to the background (or application defined) color. this avoids
adding the final composited frame to the first.
Change-Id: Ia3a52cf4482c6176334a5c9c99a0ddd07d1776e7
Marking certain frames as "do not blend" helps avoiding alpha-blending
at decode/render time.
It also helps inserting I-frames (frames which can be independently
decoded) into the animation.
Change-Id: Iaa222805db88d2f1c81104ce9d882e7c7ff8cfdb
- Add a note that disposal only applies to the frame rectangle
- Add the formula for alpha-blending.
- Note that alpha-blending would occur for the common rectangle
- Also note the case when both color profile and disposal are
present.
Change-Id: I214787dd64453edf3b0cdaff3951015281a32ee4
- provide anchor links to the bitstream chunks referenced in the
extended format section
- remove some unnecessary parenthetical notation and add some
consistency to various chunk element definitions
Change-Id: Ifd946fee81b36e4e555399555a2a58c853fdc3b7
- Add details about the VP8L chunk support.
- Also add new example bitsteams containing VP8L chunk.
- Add back a section describing the VP8 chunk.
- Restrict some fields to 16 or 24 bits instead of 32 bits.
- Fields whose values are always positive are stored 1-based
instead of 0-based.
- Unknown chunks can only occur at certain places in the file.
- Remove the restriction for some fields to be divisible by 32 or 16.
Instead they are restricted to be even.
- Add a restriction for (canvas_width * canvas_height) product.
- Add 3 bits for rotation & symmetry in VP8X flags.
- Add some new example layouts.
- Add/clarify some nitty-gritties throughout the doc.
- Use the terms frame/tile more consistently and logically.
- Update related TODOs.
Change-Id: I611c1f58ecc3ee87546ca31bad1609376fad251e
No further experiments are to be expected, so this is quite the
final format so far, pending supplemental feedbacks.
Change-Id: I2a3de025c90b7bb5fdd8792b2b2ccdc2e3753f56
- Make sure alpha flag is set in case of a lossless file with VP8X chunk.
The semantic of ALPHA_FLAG changes with this: it means the images
contain alpha (rather than ALPH chunk in particular).
- Update the mux container spec to add 1-line description of alpha
flag.
- Rename "HasLosslessImages()" to "MuxHasLosslessImages()", and other
similar function renames.
- Rename FeatureFlags to WebPFeatureFlags
- Elaborated a comment for a special case.
- A misc comment fix.
Change-Id: If212ccf4338c125b4c71c10bf281a51b3ba7ff45
now, we only use 2 bits for the filtering method, and 2 bits
for the compression method.
There's two additional bits which are INFORMATIVE, to specify
whether the source has been pre-processed (level reduction)
during compression. This can be used at decompression time
for some post-processing (see DequantizeLevels()).
New relevant spec excerpt:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ChunkHeader('ALPH') |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Rsv| P | F | C | Alpha Bitstream... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Compression method (C): 2 bits
: The compression method used:
* `0`: No compression.
* `1`: Backward reference counts encoded with arithmetic encoder.
Filtering method (F): 2 bits
: The filtering method used:
* `0`: None.
* `1`: Horizontal filter.
* `2`: Vertical filter.
* `3`: Gradient filter.
Pre-processing (P): 2 bits
: These INFORMATIVE bits are used to signal the pre-processing that has
been performed during compression. The decoder can use this information to
e.g. dither the values or smooth the gradients prior to display.
* `0`: no pre-processing
* `1`: level reduction
Decoders are not required to use this information in any specified way.
Reserved (Rsv): 2 bits
: SHOULD be `0`.
Alpha bitstream: _Chunk Size_ - `1` bytes
: Encoded alpha bitstream.
This optional chunk contains encoded alpha data for a single tile.
Either **ALL or NONE** of the tiles must contain this chunk.
The alpha channel data is losslessly stored as raw data (when
compression method is '0') or compressed using the lossless format
(when the compression method is '1').
Change-Id: Ied8f5fb922707a953e6a2b601c69c73e552dda6b
- the tile chunk size does not include the alpha or vp8 chunks that
follow
- remove 'experimental' note from alpha section
- drop an unused term from the terminology section
Change-Id: I46f0fd610bbce579446e19339c3458dddfb595f7
- split the doc into sections for simple and extended format and move
example layouts to the end.
- use ASCII tables to describe chunk formats
- attempt to consistently use MUST/SHOULD, etc.
- remove bold from most terms, but add them to definition lists which
allow for the styling to be changed.
Change-Id: I93c1cd33bde9ccf0b265b202ec4182ce98fd6b48
Updated cwebp (Webp Encoder) binary to support Alpha encoding.
Modified man page and WebP container spec appropriately.
Change-Id: I52f6a5cb3e870c386591e9a7776293fa6a8fb04b
- Add alpha support in mux.
- Remove WebPMuxAddNamedData() and WebPMuxGetNamedData() APIs. Add WebPMuxSetImage(), WebPmuxGetImage() and WebPMuxDeleteImage() APIs instead.
- Refactor code using WebPImage struct.
- Corresponding changes in webpmux binary.
- WebPMuxSetImage()/AddFrame()/AddTile() can now work with data which starts from "RIFF...". This simplifies reading a single-image webp file and adding it as an image/frame/tile in mux.
Change-Id: I7d98a6407dfe55c84a682ef7e46bc622f5a6f8d9
