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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  compres-
	      sion 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 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  usu-
	      ally in the range of 20 to 50.

       -preset string
	      Specify  a  set of pre-defined parameters to suit a particular type of source mate-
	      rial. 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 is 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 fil-
	      tering 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  algo-
	      rithm.  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 usu-
	      ally 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 informa-
	      tion: 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, seg-
	      ment, 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.  Com-
	      pressor will make several pass of partial encoding in order to get as close as pos-
	      sible to this target.

       -psnr float
	      Specify a target PSNR (in dB) to try and reach for the compressed output.  Compres-
	      sor 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.

       -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  a pre-processing filter. This option is a placeholder and has currently no
	      effect.

       -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'. Inter-
	      nally, alpha filtering is performed using four possible predictions (none, horizon-
	      tal,  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.

       -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  collo-
	      cated 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.webmproject.org/code/contrib-
       ute/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

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.

					  March 13, 2013				 CWEBP(1)
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