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  ig‐
              nored.

       -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 compress‐
              ibility,  but has minimal impact on the visual quality.  It triggers lossless compression
              mode automatically.  Range is 0 (maximum preprocessing) to 100 (no preprocessing, the de‐
              fault).

       -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  en‐
              ables  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  com‐
              pression  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 over‐
              writes 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 en‐
              coding 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 in‐
              specting 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 com‐
              pression 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 as‐
              pect-ratio.

       -crop x_position y_position width height
              Crop the source to a rectangle with top-left corner at coordinates  (x_position,  y_posi‐
              tion)  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  (typi‐
              cally).  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 cer‐
              tain 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 default, with or without alpha).

       -size int
              Specify  a  target  size (in bytes) to try and reach for the compressed output.  The com‐
              pressor 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  compres‐
              sion. This flag will generally produce an output file of similar size to its JPEG equiva‐
              lent (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 filter‐
              ing 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. Seg‐
              ments should be in range 1 to 4. Default value is 4.  This option has no effect for meth‐
              ods 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 mac‐
              roblock is skipped, which segment it belongs to, whether it is coded as intra 4x4 or  in‐
              tra  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 im‐
              ages.  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, gra‐
              dient). 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 compres‐
              sion, 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/sub‐
       mitting-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 <pascal.massimino@gmail.com>, 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)

Usage:
 cwebp [-preset <...>] [options] in_file [-o out_file]

If input size (-s) for an image is not specified, it is
assumed to be a PNG, JPEG, TIFF or WebP file.

Options:
  -h / -help ............. short help
  -H / -longhelp ......... long help
  -q <float> ............. quality factor (0:small..100:big), default=75
  -alpha_q <int> ......... transparency-compression quality (0..100),
                           default=100
  -preset <string> ....... preset setting, one of:
                            default, photo, picture,
                            drawing, icon, text
     -preset must come first, as it overwrites other parameters
  -z <int> ............... activates lossless preset with given
                           level in [0:fast, ..., 9:slowest]

  -m <int> ............... compression method (0=fast, 6=slowest), default=4
  -segments <int> ........ number of segments to use (1..4), default=4
  -size <int> ............ target size (in bytes)
  -psnr <float> .......... target PSNR (in dB. typically: 42)

  -s <int> <int> ......... input size (width x height) for YUV
  -sns <int> ............. spatial noise shaping (0:off, 100:max), default=50
  -f <int> ............... filter strength (0=off..100), default=60
  -sharpness <int> ....... filter sharpness (0:most .. 7:least sharp), default=0
  -strong ................ use strong filter instead of simple (default)
  -nostrong .............. use simple filter instead of strong
  -sharp_yuv ............. use sharper (and slower) RGB->YUV conversion
  -partition_limit <int> . limit quality to fit the 512k limit on
                           the first partition (0=no degradation ... 100=full)
  -pass <int> ............ analysis pass number (1..10)
  -crop <x> <y> <w> <h> .. crop picture with the given rectangle
  -resize <w> <h> ........ resize picture (after any cropping)
  -mt .................... use multi-threading if available
  -low_memory ............ reduce memory usage (slower encoding)
  -map <int> ............. print map of extra info
  -print_psnr ............ prints averaged PSNR distortion
  -print_ssim ............ prints averaged SSIM distortion
  -print_lsim ............ prints local-similarity distortion
  -d <file.pgm> .......... dump the compressed output (PGM file)
  -alpha_method <int> .... transparency-compression method (0..1), default=1
  -alpha_filter <string> . predictive filtering for alpha plane,
                           one of: none, fast (default) or best
  -exact ................. preserve RGB values in transparent area, default=off
  -blend_alpha <hex> ..... blend colors against background color
                           expressed as RGB values written in
                           hexadecimal, e.g. 0xc0e0d0 for red=0xc0
                           green=0xe0 and blue=0xd0
  -noalpha ............... discard any transparency information
  -lossless .............. encode image losslessly, default=off
  -near_lossless <int> ... use near-lossless image
                           preprocessing (0..100=off), default=100
  -hint <string> ......... specify image characteristics hint,
                           one of: photo, picture or graph

  -metadata <string> ..... comma separated list of metadata to
                           copy from the input to the output if present.
                           Valid values: all, none (default), exif, icc, xmp

  -short ................. condense printed message
  -quiet ................. don't print anything
  -version ............... print version number and exit
  -noasm ................. disable all assembly optimizations
  -v ..................... verbose, e.g. print encoding/decoding times
  -progress .............. report encoding progress

Experimental Options:
  -jpeg_like ............. roughly match expected JPEG size
  -af .................... auto-adjust filter strength
  -pre <int> ............. pre-processing filter