CWEBP(1) General Commands Manual CWEBP(1)
cwebp - compress an image file to a WebP file
cwebp [options] input_file -o output_file.webp
This manual page documents the cwebp command.
cwebp compresses an image using the WebP format. Input format can be either PNG, JPEG, or raw Y'CbCr samples. When using PNG, the trans-
parency information (alpha channel) is currently discarded.
The basic options are:
Specify the name of the output WebP file. If omitted, cwebp will perform compression but only report statistics.
A short usage summary.
A summary of all the possible options.
Print the version number (as major.minor.revision) and exit.
Specify the compression factor between 0 and 100. A small factor produces a smaller file with lower quality. Best quality is
achieved using a value of 100. The default is 75.
-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
smoother the picture will appear. Typical values are usually in the range of 20 to 50.
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.
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 transfer
these bits. The possible range goes from 0 (algorithm is off) to 100 (the maximal effect). The default value is 80.
-m int Specify the compression method to use. This parameter controls the tradeoff 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 is faster processing time at
the expense of larger filesize and lower compression quality.
-af Turns auto-filter on. This algorithm will spend additional time optimizing the filtering strength to reach a well-balanced quality.
More advanced options are:
Specify the sharpness of the filtering (if used). Range is 0 (sharpest) to 7 (least sharp). Default is 0.
Use a stronger filtering than the default one (if filtering is being used thanks to the -f option). Strong filtering is off by
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.
Degrade quality by limiting the number of bits used by some macroblocks. Range is 0 (no degradation, the default) to 100 (full
degradation). Useful values are usually around 30-70 for moderately large images. In the VP8 format, the so-called control parti-
tion 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, seg-
ment, 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 (PARTITION0_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.
Specify a target size (in bytes) to try and reach for the compressed output. Compressor will make several pass of partial encoding
in order to get as close as possible to this target.
Specify a target PSNR (in dB) to try and reach for the compressed output. Compressor will make several pass of partial encoding in
order to get as close as possible to this target.
Set a maximum number of pass to use during the dichotomy used by options -size or -psnr. Maximum value is 10.
-crop x_position y_position width height
Crop the source to a rectangle with top-left corner at coordinates (x_position, y_position) and size width x height. This cropping
area must be fully contained within the source rectangle.
-s width height
Specify that the input file actually consists of raw Y'CbCr samples following the ITU-R BT.601 recommendation, in 4:2:0 linear for-
mat. The luma plane has size width x height.
Output additional ASCII-map of encoding information. Possible map values range from 1 to 6. This is only meant to help debugging.
Specify a pre-processing filter. This option is a placeholder and has currently no effect.
-noasm Disable all assembly optimizations.
-v Print extra information (encoding time in particular).
-quiet Do not print anything.
-short Only print brief information (output file size and PSNR) for testing purpose.
cwebp -q 70 picture.png -o picture.webp
cwebp -sns 70 -f 50 -strong -af -size 60000 picture.png -o picture.webp
Please refer to http://code.google.com/speed/webp/ for additional information.
cwebp was written by the WebP team.
The latest source tree is available at http://www.webmproject.org/code
This manual page was written by Pascal Massimino <firstname.lastname@example.org>, for the Debian project (and may be used by others).
September 19, 2011 CWEBP(1)