Provided by: webp_0.4.4-1_amd64 bug

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  an  '-'  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.

       -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.

       -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.

       -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.

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

       -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.

       -af    Turns  auto-filter  on.  This  algorithm  will spend additional time optimizing the
              filtering strength to reach a well-balanced quality.

ADDITIONAL OPTIONS

       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.

       -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.

       -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
              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.

       -alpha_cleanup
              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.

       -noalpha
              Using this option will discard the alpha channel.

       -lossless
              Encode the image without any loss.

       -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.

       -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 purpose.

BUGS

       Please report all bugs to our 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 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  <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.

                                         October 19, 2015                                CWEBP(1)