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CWEBP(1)		    General Commands Manual		      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 a	'-' for	instance. This option must ap-
	      pear 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	trans-
	      parent 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 automati-
	      cally.   Range  is  0 (maximum preprocessing) to 100 (no prepro-
	      cessing, 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 op-
	      tion), a small factor enables faster compression speed, but pro-
	      duces a larger file.  Maximum compression	is achieved by using a
	      value of 100.

       -z int Switch on	lossless compression mode with the specified level be-
	      tween 0 and 9, with level	0 being	the fastest, 9 being the slow-
	      est. 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  compres-
	      sion. 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 de-
	      cide on the quality gain.	 Lower value can result	in faster pro-
	      cessing  time  at	the expense of larger file size	and lower com-
	      pression 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  coordi-
	      nates  (x_position,  y_position)	and size width x height.  This
	      cropping area must be fully contained within the source  rectan-
	      gle.

       -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  de-
	      fault.  Note  that leaving this flag off will have some side ef-
	      fects on the bitstream: it  forces  certain  bitstream  features
	      like  number  of	partitions (forced to 1). Note that a more de-
	      tailed report of bitstream size is printed by cwebp  when	 using
	      this option.

   LOSSY OPTIONS
       These  options  are  only  effective when doing lossy encoding (the de-
       fault, with or without alpha).

       -size int
	      Specify a	target size (in	bytes) to try and reach	for  the  com-
	      pressed output.  The compressor will make	several	passes of par-
	      tial encoding in order to	get as close as	possible to this  tar-
	      get. 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 com-
	      pressed output.  The compressor will make	several	passes of par-
	      tial  encoding in	order to get as	close as possible to this tar-
	      get. 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 qual-
	      ity.

       -jpeg_like
	      Change  the  internal  parameter mapping to better match the ex-
	      pected 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.

       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	trans-
	      fer 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.  De-
	      fault  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.

   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	debug-
	      ging.

   ADDITIONAL OPTIONS
       More advanced options are:

       -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.

       -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 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.

       -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.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 is	a part of libwebp and was written by the WebP team.
       The  latest  source  tree  is  available	 at   https://chromium.google-
       source.com/webm/libwebp

       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.

			       January 20, 2017			      CWEBP(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | BUGS | EXAMPLES | AUTHORS | SEE ALSO

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