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CWEBP(1)							      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 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.

       -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 compres‐
	      sion. 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 trans‐
	      fer  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 pro‐
	      duce  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 qual‐
	      ity.

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 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.

       -size int
	      Specify  a  target size (in bytes) to try and reach for the com‐
	      pressed 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 com‐
	      pressed 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  coordi‐
	      nates  (x_position,  y_position)	and size width x height.  This
	      cropping area must be fully contained within the source  rectan‐
	      gle.

       -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.

       -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.

       -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	 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.

       -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:
       http://code.google.com/p/webp/issues
       Patches	welcome!  See  this  page  to get started: http://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 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.mas‐
       simino@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.

			       December 12, 2013		      CWEBP(1)
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