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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, 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  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:
       https://bugs.chromium.org/p/webp
       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.

			       October 19, 2015			      CWEBP(1)
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