Commit Graph

8 Commits

Author SHA1 Message Date
Pascal Massimino
2ab4b72f53 EXPERIMENTAL: add support for alpha channel
This is a (minor) bitstream change: if the 'color_space' bit is set to '1'
(which is normally an undefined/invalid behaviour), we add extra data at the
end of partition #0 (so-called 'extensions')

Namely, we add the size of the extension data as 3 bytes (little-endian),
followed by a set of bits telling which extensions we're incorporating.
The data then _preceeds_ this trailing tags.

This is all experimental, and you'll need to have
'#define WEBP_EXPERIMENTAL_FEATURES' in webp/types.h to enable this code
(at your own risk! :))

Still, this hack produces almost-valid WebP file for decoders that don't
check this color_space bit. In particular, previous 'dwebp' (and for instance
Chrome) will recognize this files and decode them, but without the alpha
of course. Other decoder will just see random extra stuff at the end of
partition #0.

To experiment with the alpha-channel, you need to compile on Unix platform
and use PNGs for input/output.

If 'alpha.png' is a source with alpha channel, then you can try (on Unix):

  cwebp alpha.png -o alpha.webp
  dwebp alpha.webp -o test.png

cwebp now has a '-noalpha' flag to ignore any alpha information from the
source, if present.

More hacking and experimenting welcome!

Change-Id: I3c7b1fd8411c9e7a9f77690e898479ad85c52f3e
2011-04-25 23:29:39 -07:00
Pascal Massimino
cfbf88a6c4 add SSE2 functions. ~2x faster encoding on average.
For now, SSE2 functions are compiled a-minima: only on platforms
where __SSE2__ is defined. Let's later add some autoconf-based
config to enable/disable at will.

One can disable SSE2 at run-time by hooking-up VP8GetInfo.
There is a new option "-noasm" in cwebp for that.
Output should be binary the same between C and SSE2 version. If not,
that's a bug!

patch by Christian Duvivier (cduvivier at google dot com)

Change-Id: Iae006c3cdcb7e8280e846cedb94d239dab1e42ae
2011-04-22 15:34:23 -07:00
Pascal Massimino
261abb8e24 add a 'superclean' section
wipes out everything that is not needed.
Used to create the tgz archives.

Change-Id: Icbb00edb0e3a77abd0de6135c39a11d6973f9cd3
2011-03-29 10:46:36 -07:00
Pascal Massimino
f8db5d5d1c more C89-fixes
going down to strict -ansi c89 is quite overkill (no 'inline',
and /* */-style comments).
But with these fixes, the code compiles with the stringent flags:
 -Wextra -Wold-style-definition -Wmissing-prototypes
 -Wmissing-declarations and -Wdeclaration-after-statement

Change-Id: I36222f8f505bcba3d9d1309ad98b5ccb04ec17e3
2011-03-25 15:19:37 -07:00
Pascal Massimino
8bf76fe0c8 add incremental decoding
The object WebPIDecoder is available to store the
decoding state. The flow is typically:

   WebPIDecoder* const idec = WebPINew(mode);
   while (has_more_data) {
     // ... (get additional data)
     status = WebPIAppend(idec, new_data, new_data_size);
     if (status != VP8_STATUS_SUSPENDED ||
       break;
     }

     // The above call decodes the current available buffer.
     // Part of the image can now be refreshed by calling to
     // WebPIDecGetRGB()/WebPIDecGetYUV() etc.
   }
   WebPIDelete(idec);

Doing so, one can try and decode new macroblocks everytime fresh
bytes are available.
There's two operating modes: either appending fresh bytes, or
updating the whole buffer with additional data in the end.
The latter requires less memcpy()'s

main patch by Somnath Banerjee (somnath at google.com)

Change-Id: Ie81cbd0b50f175743af06b1f964de838b9a10a4a
2011-03-23 18:33:26 -07:00
Pascal Massimino
6463e6ab94 add some install instructions, and fix intel-mac flags
patch by Christian Duvivier

Change-Id: I8e38f98c6738c3d89917cd3eb88f6c095335a428
2011-03-17 14:45:23 -07:00
Pascal Massimino
d5bd54c712 fix typo and buggy line
Change-Id: I744bcfe5e611a49af9ad8a00ba764b74ee8dd727
2011-02-20 11:57:49 -08:00
Pascal Massimino
f7a9549dcb Add a simple top-level makefile.unix for quick & easy build.
Just use:
  make -f makefile.unix
instead of the autoconf system.

Change-Id: Idcedfd22e543023d1731f5753fb4958f02d0dd75
2011-02-20 11:17:44 -08:00