Commit Graph

181 Commits

Author SHA1 Message Date
James Zern
2c724968d2 cwebp/jpegdec: add JPEG metadata extraction
the values of EXIF/XMP/ICC are unused and Extended XMP for payloads >
64k is unsupported.

Change-Id: If721aa2009335ce090148b7ecd7ea8459f9b942d
2012-12-20 18:35:38 -08:00
James Zern
dba64d91bb cwebp: add PNG metadata extraction
the values of XMP/EXIF/ICC are currently unused.

Change-Id: I39d78b9a179f2d36c9c8ea12776bfdf6d8d18663
2012-12-20 18:32:09 -08:00
James Zern
2914ecfd56 cwebp/tiffdec: add TIFF metadata extraction
currently the values of XMP/ICC are unused and EXIF is ignored.

Change-Id: I1d8b73bde4db2768f117158f986aadbaaec45804
2012-12-19 18:26:05 -08:00
skal
1bd287a6e4 Cleanup around jpegdec
* change some (*func_ptr) construct to func_ptr simply.
  * remove one memcpy
  * group #include related to decoding together

Change-Id: If751cfbd9e78be75c57fb60fc9c937900c2c8fe0
2012-12-11 11:02:39 +01:00
James Zern
1c1c5646a5 cwebp: extract tiff decoding to its own module
Change-Id: If98d0d37de34b63ac10d826150237b5f99446532
2012-12-10 22:37:04 -08:00
James Zern
6a871d66a4 cwebp: extract jpeg decoding to its own module
Change-Id: I45e1f0fa7b34286dd98926e0485e5a8ab1964570
2012-12-07 20:12:46 -08:00
James Zern
2ee228f9a5 cwebp: extract png decoding to its own module
Change-Id: I80dd09fe1f1c6317e9d0cdd422438bda11b43ed5
2012-12-07 20:02:41 -08:00
James Zern
63aba3aef1 cwebp: add metadata framework
unused currently, but the intent is to allow each format to populate
exif/xmp/icc with cwebp then transferring it to the webp file.

Change-Id: I0514f62de52fa7f89c595ee7ef2ad7dced910a41
2012-12-06 14:29:10 -08:00
pascal massimino
4828bb931d Merge "cwebp (windows): fix alpha image import on XP" 2012-10-23 00:57:21 -07:00
James Zern
eda8ee4b3b cwebp (windows): fix alpha image import on XP
Query the converter to ensure the format is supported; add BGR formats
as RGBA was failing for PNG on XP

Fixes issue 129

Change-Id: I02e0d74b3b21337bc5fffd6a5dc158b7809b9aa9
2012-10-19 18:48:47 -07:00
Pascal Massimino
f86e6abe1f add LSIM metric to WebPPictureDistortion()
LSIM stands for "local similarity": before matching
a compressed pixel to the source, we search around in the source
and minimise the squared error. So, this is close to PSNR calculation,
but mitigates some of its limitations (pure translation and noise for instance).

There's a new -print_lsim option to cwebp too.

Change-Id: Ia38561034c7a90e71d2ea0f55bb1de527eda245b
2012-10-19 06:48:11 -07:00
pascal massimino
cf1e90dec7 Merge "cwebp: fix jpg encodes on XP" 2012-10-09 00:04:19 -07:00
James Zern
f2b5d19b30 [cd]webp: always output windows errors
don't hide failures with -v.

Change-Id: I46485a66f266fd9e9e8c640d1051cd22cfa40658
2012-10-08 18:36:10 -07:00
James Zern
ecd66f774d cwebp: fix jpg encodes on XP
correct has_alpha check; previously it was controlled by keep_alpha,
which overrode the source format check.
fixes issue #127

Change-Id: I949be90419b03610c64900be0fd37f83b70cbe73
2012-10-08 18:26:21 -07:00
James Zern
292ec5cc7d quiet a few 'uninitialized' warnings
spurious in this case, but addresses e.g.,
... potentially uninitialized local variable 'weighted_average' used

Change-Id: Ib99998bf49e4af7a82ee66f13fb850ca5b17dc71
2012-08-02 14:03:30 -07:00
pascal massimino
5e7963000a Merge "WebPEncode: clear stats at the start of encode" into 0.2.0 2012-08-01 12:00:09 -07:00
Vikas Arora
dd1c3873fe Add image-hint for low-color images.
For low-color images, it may be better to not use color-palettes.
Users should treat this as one another hint (as with Photo &
Picture) and another parameter for tuning the compression density.
The optimum compression can still be obtained by running (outer loop)
compression with all possible tunable parameters.

Change-Id: Icb1a4face2a84774e16e801aee4a8ae97e232e8a
2012-07-31 23:11:19 -07:00
James Zern
256afefa50 cwebp: exit immediately on version mismatch
{Picture,Config}Init don't do allocations and attempting to free any of
their contents on version mismatch will likely cause a crash

Change-Id: I2a5aece235f9680fb406aec4799adceea7f62cfc
2012-07-27 19:58:58 -07:00
James Zern
475d87d767 WebPEncode: clear stats at the start of encode
also relocate user_data from WebPAuxStats to the WebPPicture struct to
make clearing easier while placing it closer to the progress hook with
which it's used.
prior to this change some spurious lossless data could be reported in
the lossy (sans alpha) encoding case. additionally user_data could be
lost during lossless encoding.

Change-Id: I929fae3dfde4d445ff81bbaad51445ea586dd80b
2012-07-27 19:57:18 -07:00
Pascal Massimino
7d853d79dc add stats for lossless
* Extend AuxStats with new fields
  it's slightly ABI-incompatible, but i guess it's ok for 0.1.99+
  I expect to add more stats later, possibly (predictor stats, etc.)
* Have cwebp report the features used by lossless
  compression (either for alpha or full lossless coding)
* Print the PSNR for alpha (useful in case of -alpha_q)
* clean-up alpha.c signatures
+ misc cleanup (added const '* const ptr', etc.)

Change-Id: I157a21581f1793cb0c6cc0882e7b0a2dde68a970
2012-07-24 16:17:13 -07:00
James Zern
3e5bbe1c2e Merge "rename 'use_argb_input' to 'use_argb'" into 0.2.0 2012-07-18 23:26:42 -07:00
Pascal Massimino
0275159143 add a very crude progress report for lossless
better than nothing. Removed the warning in cwebp.c
(and silenced the warning in quiet mode too)

Change-Id: I85bbeaf77e0f60ead798886043dc053e6b44def5
2012-07-18 22:54:50 -07:00
Pascal Massimino
dd1081763c rename 'use_argb_input' to 'use_argb'
long name, and there's not really an 'output' equivalent

Change-Id: I9133ff734ae8d6572cb2f607211361f011fc0bc1
2012-07-18 22:47:16 -07:00
James Zern
12f9aede7e README: update cwebp help output
Change-Id: Ifc2fafca8131e53a894056e37bb22d25fedfa150
2012-07-13 14:55:39 -07:00
pascal massimino
0e09732c5e Merge "cwebp: fix crash with yuv input + lossless" 2012-07-02 14:40:00 -07:00
James Zern
7bda392b50 cwebp: fix crash with yuv input + lossless
Change-Id: Ia27c925f532a4243369288e954abdc063b9f94f9
2012-07-02 14:33:25 -07:00
James Zern
d8921dd4e6 cwebp: name InputFileFormat members consistently
append an '_'. TIFF introduced TIFF_ to avoid a name clash.

Change-Id: Iebe484d43aeb8e1912cd5bd10d36e1c5e66a4b42
2012-07-02 11:24:23 -07:00
James Zern
6f76d246ba cwebp: add basic TIFF support
Change-Id: I29f354e1ef9cf8f23002cf2e15814a53a94b4ed5
2012-07-02 11:22:52 -07:00
Vikas Arora
d373076a53 Added image characteristic hint for the codec.
This image type hint is used by codec to apply appropriate set of
transform filters to the image.

Change-Id: Ibb24e47ba14c40fa7f9f2c50ae86e03f2b29e9a6
2012-06-22 14:03:46 +05:30
Pascal Massimino
31b68fe639 cleanup WebPPicture struct and API
* add a real proper pointer for holding memory chunk pointer
  (instead of using y and argb fields)
* polish the doc with details
* add a WebPPictureView() that extract a view from a picture
  without any copy (kind of a fast-crop).
* properly snap the top-left corner for Crop/View. Previously,
  the luma position was not snapped, and was off compared to the chroma.

Change-Id: I8a3620c7f5fc6f7d1f8dd89d9da167c91e237439
2012-06-21 00:30:43 -07:00
Vikas Arora
b7fb0ed567 Log warning for unsupported options for lossless.
Change-Id: I30d4e775959c7a4a8f5b649c8c90a4edb8cced47
2012-06-20 10:51:50 +05:30
Pascal Massimino
78f3e34504 Enable lossless encoder code
Remove USE_LOSSLESS_ENCODER compile flag
Update Makefile.am and makefile.unix

Change-Id: If7080c4d8f37994c7c784730c5e547bb0a851455
2012-06-13 00:26:58 -07:00
James Zern
c71ff9e359 cwebp: fix alpha reporting in stats output
Since
 437999f introduce a generic WebPPictureHasTransparency() function
lossy encodes will not encode alpha if the alpha channel is completely
opaque.

Change-Id: I1826669c3932483650d7f8ce806cfebd4e5225fc
2012-06-07 17:32:29 -07:00
Pascal Massimino
437999fb77 introduce a generic WebPPictureHasTransparency() function
VP8-lossy will now avoid writing an ALPH chunk if the
alpha values are trivial.

+ changed DumpPicture() accordingly in cwebp
+ prevented the -d option to be active with lossless
 (DumpPicture wouldn't work).

Change-Id: I34fdb108a2b6207e93fa6cd00b1d2509a8e1dc4b
2012-06-04 16:17:55 -07:00
James Zern
00b29e282f normalize example header includes
headers from examples/ aren't installed so prefix with './' to be
explicit.

Change-Id: Ie6c1544a026a9859b7fc0cf238b21e031ef0013f
2012-05-15 13:48:11 -07:00
James Zern
1d38b258b8 cwebp/windows: use MAKE_REFGUID where appropriate
Change-Id: If595c75a833d37df86c16bf926da5f032015c68e
2012-05-09 11:52:01 -07:00
James Zern
817ef6e9af Merge "cwebp: fix WIC/Microsoft SDK compatibility issue" 2012-05-09 11:50:05 -07:00
James Zern
902d3e3b5f cwebp: fix WIC/Microsoft SDK compatibility issue
Fixes issue #115.
Define local copies of GUID_WICPixelFormat24bppRGB &
GUID_WICPixelFormat32bppRGBA (and GUID_WICPixelFormat32bppBGRA for
symmetry) to avoid link issues when building against older versions of
the SDK.

Change-Id: I2a26be1b7fe6d970feb3211cf0059e5898e3028d
2012-05-09 11:47:15 -07:00
Pascal Massimino
4abe04a204 fix the return value and handle missing input file case.
Change-Id: I42a64fcf7587ff3a487115808e2cfa51cec0031d
2012-05-09 00:34:30 -07:00
Vikas Arora
c4ccab6463 Print relevant lossless encoding stats in cwebp.
Change-Id: Ib8dfab498b1a05e49734bba2d3e72810343e8b0a
2012-05-09 11:31:41 +05:30
Pascal Massimino
72920caa61 introduce -lossless option, protected by USE_LOSSLESS_ENCODER
Change-Id: Ic5707082fefd964b9bcab0c9f9aa276992c22b06
2012-05-07 14:25:02 -07:00
James Zern
a0b2736d79 cosmetics & warnings
- remove some unused functions
- move global arrays from data to read only section
- explicitly cast malloc returns; not specifically necessary, but helps
  show intent
- miscellaneous formatting

Change-Id: Ib15fe5b37fe6c29c369ad928bdc3a7290cd13c84
2012-01-30 17:19:53 -08:00
James Zern
974aaff360 examples: logging updates
- send errors to stderr
- send help to stdout
- add image size to webpmux -info output and send to stdout
- correct webpmux exit values

Change-Id: Ifd8e8493aab33a82765f7b7903cef345d96da9ae
2012-01-24 16:55:38 -08:00
Pascal Massimino
d61479f95b add -print_psnr and -print_ssim options to cwebp.
These will report the 7x7-averaged PSNR or SSIM, using the
new internal function WebPPictureDistortion().
This is for information only. These flags have no encoding impact.

+misc opportunistic cosmetics

Change-Id: I64c0a7eca679134d39062e438886274b22bb643f
2012-01-20 07:37:29 -08:00
Pascal Massimino
2e3e8b2ef5 add a WebPCleanupTransparentArea() method
to 'clean up' the fully-transparent area and make it more compressible
new cwebp flags: -alpha_cleanup (off by default, since gain is not 100% guaranteed)

Change-Id: I74d77e1915eee146584cd61c9c1132a41db922eb
2012-01-18 14:01:24 -08:00
Pascal Massimino
8ca2076de1 Introduce a 'fast' alpha mode
.. where only 2 filtering modes are potentially
tried, instead of all of them. This is fast than the exhaustive 'best'
mode, and not much worse.

Options for cwebp are:
 -alpha_filter none
 -alpha_filter fast      (<- default)
 -alpha_filter best      (<- slow)

Change-Id: I8cb90ee11b8f981811e013ea4ad5bf72ba3ea7d4
2012-01-09 02:37:44 -08:00
James Zern
ad1e163a0d cosmetics: normalize copyright headers
Change-Id: I5e2462b101e0447a4f15a1455c07131bc97a52dd
2012-01-06 14:49:06 -08:00
Vikas Arora
252028aaac Add predictive filtering option for Alpha.
Add predictive filtering option for Alpha plane.
Valid range for filter option is [0, 5] corresponding to prediction
methods none, horizontal, vertical, gradient & paeth filter.
The prediction method 5 will try all the prediction methods (0 to 4)
and pick the prediction method that gives best compression.

Change-Id: I9244d4a9c5017501a9696c7cec5045f04c16d49b
2012-01-05 13:55:35 +05:30
Pascal Massimino
30971c9e95 Implement progress report (and user abort)
New cwebp flag is -progress

Change-Id: Ied872cca13f512036860783bbee1bdbccad72768
2011-12-01 14:19:40 -08:00
Pascal Massimino
d71fbdcca3 fix small typo in error message array
Change-Id: If34537e53cc56b5f5daa15afaefb1f49d11602f5
2011-12-01 03:34:22 -08:00
Vikas Arora
a0ec9aace9 Update WebP encoder (cwebp) to support Alpha.
Updated cwebp (Webp Encoder) binary to support Alpha encoding.
Modified man page and WebP container spec appropriately.

Change-Id: I52f6a5cb3e870c386591e9a7776293fa6a8fb04b
2011-12-01 15:13:17 +05:30
Urvang Joshi
372e2b463b Correct a bug in ReadPNG() with GRAY_ALPHA images
Change-Id: I4676160ee544ed914cc0de3f9cd140d9ee65addc
2011-11-16 18:56:23 -08:00
James Zern
04e84cf1f1 examples: slight cleanup
spelling/indent/condense a few lines
removal/restriction of extern "C" usage
add const where applicable

Change-Id: Idd49b3498b1d7fc391724b4cde63706022217cb0
2011-11-04 15:30:28 -07:00
Pascal Massimino
f6a7d75885 remove useless test
Change-Id: I1b31842ddf719ddcc185a5d6a5032a20d5e593e2
2011-11-01 05:18:46 -07:00
Pascal Massimino
28ad70c56d Fix PNG decoding bug
some png with palette-based alpha channels were incorrectly
treated as alpha-less, causing segfault.

Change-Id: I03883590f9539848d5135d359b6f105d2b14329f
2011-09-20 07:59:43 -07:00
Pascal Massimino
e06ac0887f create a separate libwebpdsp under src/dsp
Gathers all DSP-related function (and SSE2 implementations).
Clean-up some unwanted symbolic dependencies so that webp_encode,
webp_decode and webp_dsp are truly independent libraries.

+ opportunistic clean-up:
  * remove unneeded VP8DspInitTables(), now integrated in VP8DspInit()
  * make consistent use of VP8GetCPUInfo() in the various DspInit() funcs
  * change OUT macro to DST
2011-09-13 12:29:44 -07:00
Pascal Massimino
a5b78c81b5 wrap alpha-related options under WEBP_EXPERIMENTAL_FEATURES flag
Change-Id: I6d8f4b4ec7dca53054e28b969a536e7c93c1e5e2
2011-08-29 22:04:46 -07:00
Mikolaj Zalewski
2aa6b80efe Slience some Visual Studio warnings.
Change-Id: I62078af80bfcaa82bdc165fc2fc8fce2d2aad862
2011-08-29 10:37:13 +02:00
James Zern
c7e86abab6 cosmetics: fix comment line lengths
add additional '-' to //----... style comments globally instead of
polluting further commits

Change-Id: I951acc68b7b5384b4d6e235349b0067d1aa6fa8b
2011-08-26 12:19:33 -07:00
Pascal Massimino
900286e091 add a -partition_limit option to limit the number of bits used by intra4x4
Although it degrades quality, this option is useful to avoid the 512k
limit for partition #0.
If not enough to reach the lower bound of 4bits per macroblock header,
one should also limit the number of segments used (down to -segments 1)

See the man file for extra details.

Change-Id: Ia59ffac13176c85b809ddd6340d37b54ee9487ea
2011-08-23 15:58:22 -07:00
James Zern
b4d0ef8f58 Makefile.vc: add DLL configs
(release|debug)-dynamic
These configurations will produce a dll in bin/ and an import lib under
lib/.
Currently the -noasm switch in the examples will be disabled for these
builds due to a dependency on VP8EncGetCPUInfo.

Change-Id: I2cbac0064f0e500698d14ffc03200791ca837090
2011-07-15 15:25:02 -07:00
James Zern
3827e1bce4 Merge "examples: (windows/WIC) add alpha support" 2011-07-08 14:10:17 -07:00
Pascal Massimino
5142a0be3a export alpha channel (if present) when dumping to PGM format
Change-Id: Ica1818937fa03b29a749887d28f49fe675c8b1db
2011-07-07 16:08:15 -07:00
James Zern
0805706252 examples: quiet warnings
When WEBP_HAVE_(JPEG|PNG) were undefined the stub functions would
produce warnings for unused parameters.

Change-Id: I79b2457c769d1f9382be834162de019c5427f94b
2011-06-24 16:50:02 -04:00
James Zern
3cfe0888ae examples: (windows/WIC) add alpha support
Portions based on a patch by Ismail Keskin (iskeskin at gmail dot com)
Fixes issue #83.

Change-Id: Ib54188910354240a2731b0a3a3d0915d17af2233
2011-06-22 12:01:48 -07:00
pascal massimino
ea43f045b5 Merge "configure: mingw32 targets: test for WIC support" 2011-06-10 16:11:51 -07:00
Pascal Massimino
a11009d7fc SSE2 version of simple in-loop filtering
~10% faster decoding

Patch by Somnath Banerjee (somnath at google dot com)

Change-Id: I200db408272b4f61cda9d9261d2d4370a698d6c4
2011-06-10 15:10:18 -07:00
James Zern
31f9dc6fdd configure: mingw32 targets: test for WIC support
Replace usage of _WIN32 in examples as this does not guarantee the
presence of wincodec.h.
mingw-w64 notably includes wincodec.h, though other releases do not.

Under cygwin the following can be used for a WIC enabled binary:
./configure --target=i686-pc-mingw32 CC=i686-w64-mingw32-gcc.exe

Change-Id: Ica6a714c3356a8eaf88486a1c3f5aa6adde394c0
2011-06-08 11:32:41 -07:00
Pascal Massimino
ca7a2fd66d Add error reporting from encoding failures.
picture->error_code can be looked up for finer error diagnose.
Added readable error messages to cwebp too.

Should close bug #75 (http://code.google.com/p/webp/issues/detail?id=75)

Change-Id: I8889d06642d90702f698cd5c27441a058ddb3636
2011-06-02 07:06:39 -07:00
Pascal Massimino
842c009b38 fix -strong option
was checking the presence of a useless second argument

Change-Id: I2c524a79fc7317cb8b6146c10265ee9462cd1958
2011-05-05 18:10:08 -07:00
Pascal Massimino
38369c03e0 cosmetics
Change-Id: I39c3bc671ab427dcb3e23aedee7fe8d81f4cb860
2011-05-04 23:25:40 -07:00
Pascal Massimino
6d0e66c23e prepare experimentation with yuv444 / 422
+ add a simple rescaling function: WebPPictureRescale() for encoding
+ clean-up the memory managment around the alpha plane
+ fix some includes path by using "../webp/xxx.h" instead of "webp/xxx.h"

New flags for 'cwebp':
 -resize <width> <height>
 -444  (no effect)
 -422  (no effect)
 -400

Change-Id: I25a95f901493f939c2dd789e658493b83bd1abfa
2011-05-04 15:41:08 -07:00
Pascal Massimino
f7d9e261c5 fix merge problems
Change-Id: I6d0763734139d2852896872c80c5e7fa7889945a
2011-04-26 11:02:38 -07:00
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
4b0b0d66cc cwebp: use modern functions
patch by Jan Engelhardt (jengelh at medozas dot de)

Change-Id: I0e1766469fc4bc229488018b30416e3359c43012
2011-03-26 09:27:45 -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
650ffa3bbb add version getters for decoder and encoder
WebPGetDecoderVersion() and WebPGetEncoderVersion()
will not return 0.1.2 encoded as 0x000102

dwebp and cwebp also have a new "-version" flag

Change-Id: I4fb4b5a8fc4e53681a386ff4b74fffb639fa237a
2011-03-24 16:17:10 -07:00
Pascal Massimino
6d978a6c8c add error messages
patch by Christian Duvivier

Change-Id: Iaea71f690b99e313561d0284759531b81c10d7e5
2011-03-17 14:53:57 -07:00
Pascal Massimino
0744e8420e Dont' open output file until we're sure the input file is valid
fixes http://code.google.com/p/webp/issues/detail?id=48

Change-Id: I9ce2e500623380ba71ae0e2c8faf80db4568ae50
2011-02-25 12:03:27 -08:00
Pascal Massimino
f61d14aabf a WebP encoder
converts PNG & JPEG to WebP

This is an experimental early version, with lot of room
of later optimizations in both speed and quality.

Compile with the usual `./configure && make`
Command line example is examples/cwebp

Usage:

   cwebp [options] -q quality input.png -o output.webp

where 'quality' is between 0 (poor) to 100 (very good).
Typical value is around 80.

More encoding options with 'cwebp -longhelp'

Change-Id: I577a94f6f622a0c44bdfa9daf1086ace89d45539
2011-02-18 23:54:59 -08:00