Man

Command Section
CWEBP(1)                FreeBSD 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
              transparent 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
              automatically.  Range is 0 (maximum preprocessing) to 100 (no
              preprocessing, 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
              compression. 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
              coordinates (x_position, y_position) and size width x height.
              This cropping area must be fully contained within the source
              rectangle.

       -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
              compressed output.  The compressor will make several passes of
              partial encoding in order to get as close as possible to this
              target. 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
              compressed output.  The compressor will make several passes of
              partial encoding in order to get as close as possible to this
              target. 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
              quality.

       -jpeg_like
              Change the internal parameter mapping to better match the
              expected size of JPEG compression. This flag will generally
              produce 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
              transfer 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
              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 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
              (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.

   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
              debugging.

   ADDITIONAL OPTIONS
       More advanced options are:

       -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 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
              slowness 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.
              Algorithm 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.webmproject.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.googlesource.com/webm/libwebp

       This manual page was written by Pascal Massimino
       <[email protected]>, for the Debian project (and may be used
       by others).

SEE ALSO
       dwebp(1), gif2webp(1)
       Please refer to http://developers.google.com/speed/webp/ for additional
       information.

                               January 20, 2017                       CWEBP(1)
Command Section