Provided by: webp_0.4.0-4_amd64 bug


       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,
       TIFF or raw Y'CbCr samples.


       The basic options are:

       -o string
              Specify the  name  of  the  output  WebP  file.  If  omitted,  cwebp  will  perform
              compression but only report statistics.

       -h, -help
              A short usage summary.

       -H, -longhelp
              A summary of all the possible options.

              Print the version number (as major.minor.revision) and exit.

       -q float
              Specify  the  compression factor for RGB channels between 0 and 100. The default is
              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.

       -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.

       -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.

       -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.

       -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 80.

       -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.

              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.

       -mt    Use  multi-threading  for encoding, if possible. This option is only effective when
              using lossy compression on a source with a transparency channel.

              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.

       -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:

       -sharpness int
              Specify  the  sharpness  of  the  filtering  (if used).  Range is 0 (sharpest) to 7
              (least sharp). Default is 0.

              Use strong filtering (if filtering is being used thanks to the -f  option).  Strong
              filtering is on by default.

              Disable  strong  filtering (if filtering is being used thanks to the -f option) and
              use simple filtering instead.

       -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.

       -size int
              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.

       -psnr float
              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.

       -pass int
              Set a maximum number of passes to use during the dichotomy used by options -size or
              -psnr. Maximum value is 10.

       -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.

       -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.

       -map int
              Output additional ASCII-map of encoding information. Possible map values range from
              1 to 6. This is only meant to help debugging.

       -pre int
              Specify  some  pre-processing  steps.  Using  a  value of '2' will trigger quality-
              dependent pseudo-random dithering during RGBA->YUVA conversion  (lossy  compression

       -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.

              Modify  unseen  RGB  values  under fully transparent area, to help compressibility.
              The default is off.

       -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.

              Using this option will discard the alpha channel.

              Encode the image without any loss.

       -hint string
              Specify the hint about input image type. Possible values  are:  photo,  picture  or

       -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.

       -v     Print extra information (encoding time in particular).

              Compute and report average PSNR (Peak-Signal-To-Noise ratio).

              Compute   and   report   average   SSIM   (structural   similarity   metric,    see
     for additional details).

              Compute  and  report  local  similarity  metric  (sum  of  lowest error amongst the
              collocated pixel neighbors).

              Report encoding progress in percent.

       -quiet Do not print anything.

       -short Only print brief information (output file size and PSNR) for testing purpose.


       Please report all bugs to our issue tracker:
       Patches       welcome!       See       this       page       to        get        started:


       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


       cwebp was written by the WebP team.
       The latest source tree is available at

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


       dwebp(1), gif2webp(1)
       Please refer to for additional information.

                                        December 12, 2013                                CWEBP(1)