Provided by: webp_0.6.1-2_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 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 <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)