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.  Note: Animated PNG
       and WebP files are not supported.

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  ap-
              pear 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
              Specify the level of near-lossless image preprocessing. This op-
              tion adjusts pixel values to help compressibility, but has mini-
              mal  impact on the visual quality. It triggers lossless compres-
              sion mode automatically. The range is 0 (maximum  preprocessing)
              to  100  (no  preprocessing,  the default). The typical value is
              around 60. Note that lossy with -q 100 can at times yield better
              results.

       -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  op-
              tion), a small factor enables faster compression speed, but pro-
              duces a larger file.  Maximum compression is achieved by using a
              value of 100.

       -z int Switch on lossless compression mode with the specified level be-
              tween 0 and 9, with level 0 being the fastest, 9 being the slow-
              est.  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  de-
              cide on the quality gain.  Lower value can result in faster pro-
              cessing time at the expense of larger file size and  lower  com-
              pression quality.

       -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.  Note: the cropping is applied before any scaling.

       -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.  Note:
              scaling is applied after cropping.

       -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  de-
              fault.  Note  that leaving this flag off will have some side ef-
              fects on the bitstream: it  forces  certain  bitstream  features
              like  number  of  partitions (forced to 1). Note that a more de-
              tailed report of bitstream size is printed by cwebp  when  using
              this option.


   LOSSY OPTIONS
       These  options  are  only  effective when doing lossy encoding (the de-
       fault, 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.

       -qrange int int
              Specifies  the permissible interval for the quality factor. This
              is particularly useful when using multi-pass (-size or -psnr op-
              tions).   Default  is  0  100.  If the quality factor is outside
              this range, it will be clamped.  If the minimum  value  must  be
              less or equal to the maximum one.

       -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 ex-
              pected 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.  De-
              fault  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 https://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: https://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).


SEE ALSO
       dwebp(1), gif2webp(1)
       Please refer  to  https://developers.google.com/speed/webp/  for  addi-
       tional information.



                                March 17, 2022                        CWEBP(1)
