cwebp - compress an image file to a WebP file
cwebp [options] input_file -o output_file.webp
CWEBP(1) General Commands Manual CWEBP(1)
NAME
cwebp - compress an image file to a WebP file
SYNOPSIS
cwebp [options] input_file -o output_file.webp
DESCRIPTION
This manual page documents the cwebp command.
cwebp compresses an image using the WebP format. Input format can be
either PNG, JPEG, TIFF, WebP or raw Y'CbCr samples.
OPTIONS
The basic options are:
-o string
Specify the name of the output WebP file. If omitted, cwebp will
perform compression but only report statistics. Using "-" as
output name will direct output to 'stdout'.
-- string
Explicitly specify the input file. This option is useful if the
input file starts with a '-' for instance. This option must
appear last. Any other options afterward will be ignored.
-h, -help
A short usage summary.
-H, -longhelp
A summary of all the possible options.
-version
Print the version number (as major.minor.revision) and exit.
-lossless
Encode the image without any loss. For images with fully trans-
parent area, the invisible pixel values (R/G/B or Y/U/V) will be
preserved only if the -exact option is used.
-near_lossless int
Use near-lossless image preprocessing. This option adjusts pixel
values to help compressibility, but has minimal impact on the
visual quality. It triggers lossless compression mode automati-
cally. Range is 0 (maximum preprocessing) to 100 (no prepro-
cessing, the default).
-q float
Specify the compression factor for RGB channels between 0 and
100. The default is 75.
In case of lossy compression (default), a small factor produces
a smaller file with lower quality. Best quality is achieved by
using a value of 100.
In case of lossless compression (specified by the -lossless
option), a small factor enables faster compression speed, but
produces a larger file. Maximum compression is achieved by
using a value of 100.
-z int Switch on lossless compression mode with the specified level
between 0 and 9, with level 0 being the fastest, 9 being the
slowest. Fast mode produces larger file size than slower ones. A
good default is -z 6. This option is actually a shortcut for
some predefined settings for quality and method. If options -q
or -m are subsequently used, they will invalidate the effect of
this option.
-alpha_q int
Specify the compression factor for alpha compression between 0
and 100. Lossless compression of alpha is achieved using a
value of 100, while the lower values result in a lossy compres-
sion. The default is 100.
-preset string
Specify a set of pre-defined parameters to suit a particular
type of source material. Possible values are: default, photo,
picture, drawing, icon, text. Since -preset overwrites the other
parameters' values (except the -q one), this option should
preferably appear first in the order of the arguments.
-m int Specify the compression method to use. This parameter controls
the trade off between encoding speed and the compressed file
size and quality. Possible values range from 0 to 6. Default
value is 4. When higher values are used, the encoder will spend
more time inspecting additional encoding possibilities and
decide on the quality gain. Lower value can result in faster
processing time at the expense of larger file size and lower
compression quality.
-resize width height
Resize the source to a rectangle with size width x height. If
either (but not both) of the width or height parameters is 0,
the value will be calculated preserving the aspect-ratio.
-crop x_position y_position width height
Crop the source to a rectangle with top-left corner at coordi-
nates (x_position, y_position) and size width x height. This
cropping area must be fully contained within the source rectan-
gle.
-mt Use multi-threading for encoding, if possible.
-low_memory
Reduce memory usage of lossy encoding by saving four times the
compressed size (typically). This will make the encoding slower
and the output slightly different in size and distortion. This
flag is only effective for methods 3 and up, and is off by
default. Note that leaving this flag off will have some side
effects on the bitstream: it forces certain bitstream features
like number of partitions (forced to 1). Note that a more
detailed report of bitstream size is printed by cwebp when using
this option.
LOSSY OPTIONS
These options are only effective when doing lossy encoding (the
default, with or without alpha).
-size int
Specify a target size (in bytes) to try and reach for the com-
pressed output. The compressor will make several passes of par-
tial encoding in order to get as close as possible to this tar-
get. If both -size and -psnr are used, -size value will prevail.
-psnr float
Specify a target PSNR (in dB) to try and reach for the com-
pressed output. The compressor will make several passes of par-
tial encoding in order to get as close as possible to this tar-
get. If both -size and -psnr are used, -size value will prevail.
-pass int
Set a maximum number of passes to use during the dichotomy used
by options -size or -psnr. Maximum value is 10, default is 1.
If options -size or -psnr were used, but -pass wasn't specified,
a default value of '6' passes will be used.
-af Turns auto-filter on. This algorithm will spend additional time
optimizing the filtering strength to reach a well-balanced qual-
ity.
-jpeg_like
Change the internal parameter mapping to better match the
expected size of JPEG compression. This flag will generally pro-
duce an output file of similar size to its JPEG equivalent (for
the same -q setting), but with less visual distortion.
Advanced options:
-f int Specify the strength of the deblocking filter, between 0 (no
filtering) and 100 (maximum filtering). A value of 0 will turn
off any filtering. Higher value will increase the strength of
the filtering process applied after decoding the picture. The
higher the value the smoother the picture will appear. Typical
values are usually in the range of 20 to 50.
-sharpness int
Specify the sharpness of the filtering (if used). Range is 0
(sharpest) to 7 (least sharp). Default is 0.
-strong
Use strong filtering (if filtering is being used thanks to the
-f option). Strong filtering is on by default.
-nostrong
Disable strong filtering (if filtering is being used thanks to
the -f option) and use simple filtering instead.
-sharp_yuv
Use more accurate and sharper RGB->YUV conversion if needed.
Note that this process is slower than the default 'fast'
RGB->YUV conversion.
-sns int
Specify the amplitude of the spatial noise shaping. Spatial
noise shaping (or sns for short) refers to a general collection
of built-in algorithms used to decide which area of the picture
should use relatively less bits, and where else to better trans-
fer these bits. The possible range goes from 0 (algorithm is
off) to 100 (the maximal effect). The default value is 50.
-segments int
Change the number of partitions to use during the segmentation
of the sns algorithm. Segments should be in range 1 to 4.
Default value is 4. This option has no effect for methods 3 and
up, unless -low_memory is used.
-partition_limit int
Degrade quality by limiting the number of bits used by some mac-
roblocks. Range is 0 (no degradation, the default) to 100 (full
degradation). Useful values are usually around 30-70 for moder-
ately large images. In the VP8 format, the so-called control
partition has a limit of 512k and is used to store the following
information: whether the macroblock is skipped, which segment it
belongs to, whether it is coded as intra 4x4 or intra 16x16
mode, and finally the prediction modes to use for each of the
sub-blocks. For a very large image, 512k only leaves room to
few bits per 16x16 macroblock. The absolute minimum is 4 bits
per macroblock. Skip, segment, and mode information can use up
almost all these 4 bits (although the case is unlikely), which
is problematic for very large images. The partition_limit factor
controls how frequently the most bit-costly mode (intra 4x4)
will be used. This is useful in case the 512k limit is reached
and the following message is displayed: Error code: 6 (PARTI-
TION0_OVERFLOW: Partition #0 is too big to fit 512k). If using
-partition_limit is not enough to meet the 512k constraint, one
should use less segments in order to save more header bits per
macroblock. See the -segments option.
LOGGING OPTIONS
These options control the level of output:
-v Print extra information (encoding time in particular).
-print_psnr
Compute and report average PSNR (Peak-Signal-To-Noise ratio).
-print_ssim
Compute and report average SSIM (structural similarity metric,
see http://en.wikipedia.org/wiki/SSIM for additional details).
-print_lsim
Compute and report local similarity metric (sum of lowest error
amongst the collocated pixel neighbors).
-progress
Report encoding progress in percent.
-quiet Do not print anything.
-short Only print brief information (output file size and PSNR) for
testing purposes.
-map int
Output additional ASCII-map of encoding information. Possible
map values range from 1 to 6. This is only meant to help debug-
ging.
ADDITIONAL OPTIONS
More advanced options are:
-s width height
Specify that the input file actually consists of raw Y'CbCr sam-
ples following the ITU-R BT.601 recommendation, in 4:2:0 linear
format. The luma plane has size width x height.
-pre int
Specify some preprocessing steps. Using a value of '2' will
trigger quality-dependent pseudo-random dithering during
RGBA->YUVA conversion (lossy compression only).
-alpha_filter string
Specify the predictive filtering method for the alpha plane. One
of 'none', 'fast' or 'best', in increasing complexity and slow-
ness order. Default is 'fast'. Internally, alpha filtering is
performed using four possible predictions (none, horizontal,
vertical, gradient). The 'best' mode will try each mode in turn
and pick the one which gives the smaller size. The 'fast' mode
will just try to form an a priori guess without testing all
modes.
-alpha_method int
Specify the algorithm used for alpha compression: 0 or 1. Algo-
rithm 0 denotes no compression, 1 uses WebP lossless format for
compression. The default is 1.
-exact Preserve RGB values in transparent area. The default is off, to
help compressibility.
-blend_alpha int
This option blends the alpha channel (if present) with the
source using the background color specified in hexadecimal as
0xrrggbb. The alpha channel is afterward reset to the opaque
value 255.
-noalpha
Using this option will discard the alpha channel.
-hint string
Specify the hint about input image type. Possible values are:
photo, picture or graph.
-metadata string
A comma separated list of metadata to copy from the input to the
output if present. Valid values: all, none, exif, icc, xmp.
The default is none.
Note: each input format may not support all combinations.
-noasm Disable all assembly optimizations.
BUGS
Please report all bugs to the issue tracker:
https://bugs.chromium.org/p/webp
Patches welcome! See this page to get started: http://www.webmpro-
ject.org/code/contribute/submitting-patches/
EXAMPLES
cwebp -q 50 -lossless picture.png -o picture_lossless.webp
cwebp -q 70 picture_with_alpha.png -o picture_with_alpha.webp
cwebp -sns 70 -f 50 -size 60000 picture.png -o picture.webp
cwebp -o picture.webp -- ---picture.png
AUTHORS
cwebp is a part of libwebp and was written by the WebP team.
The latest source tree is available at https://chromium.google-
source.com/webm/libwebp
This manual page was written by Pascal Massimino <pascal.mas-
simino@gmail.com>, for the Debian project (and may be used by others).
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+-----------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------------+
|Availability | image/library/libwebp |
+---------------+-----------------------+
|Stability | Pass-through volatile |
+---------------+-----------------------+
SEE ALSO
dwebp(1), gif2webp(1)
Please refer to http://developers.google.com/speed/webp/ for additional
information.
NOTES
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from http://downloads.webmpro-
ject.org/releases/webp/libwebp-1.0.0-rc3.tar.gz
Further information about this software can be found on the open source
community website at https://www.webmproject.org/.
January 20, 2017 CWEBP(1)