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OPTIPNG(1)									       OPTIPNG(1)

NAME
       OptiPNG - Optimize Portable Network Graphics files

SYNOPSIS
       optipng [-? | -h | -help]
       optipng [options...] files...

DESCRIPTION
       The OptiPNG program shall attempt to optimize PNG files, i.e. reduce their size to a mini-
       mum, without losing semantic information. In addition, this program shall perform a  suite
       of  auxiliary functions like integrity checks, metadata recovery and pixmap-to-PNG conver-
       sion.

       The optimization attempts are not guaranteed to succeed. Valid PNG files  that  cannot  be
       optimized by this program are normally left intact; their size will not grow. The user may
       request to override this default behavior.

FILES
       The input files are raster image files encoded either in PNG format (the  native  format),
       or  in  an external format. The currently supported external formats are GIF, BMP, PNM and
       TIFF.

       OptiPNG processes each image file given in the command line as follows:

       - If the image is in PNG format:

	      Attempts to optimize the given file in-place. If optimization is successful, or  if
	      the  option  -force  is enabled, replaces the original file with its optimized ver-
	      sion. The original file is backed up if the option -keep is enabled.

       - If the image is in an external format:

	      Creates an optimized PNG version of the given file. The output file  name  is  com-
	      posed from the original file name and the .png extension.

       Existing files are not overwritten, unless the option -clobber is enabled.

OPTIONS
   General options
       -?, -h, -help
	      Show a complete summary of options.

       -backup, -keep
	      Keep a backup of the modified files.

       -clobber
	      Overwrite the existing output and backup files.
	      Under  this  option,  if	the option -backup is not enabled, the old backups of the
	      overwritten files are deleted.

       -dir directory
	      Write the output files to directory.

       -fix   Enable error recovery. This option has no effect on valid input files.
	      The program will spend a reasonable amount of effort to recover  as  much  data  as
	      possible, without increasing the output file size, but the success cannot be gener-
	      ally guaranteed. The program may even increase the file size, e.g., by reconstruct-
	      ing  missing critical data. Under this option, integrity shall take precedence over
	      file size.
	      When this option is not used, the invalid input files are left unprocessed.

       -force Enforce writing of a new output file.
	      This option overrides the program's decision not to write such file, e.g. when  the
	      PNG  input  is digitally signed (using dSIG), or when the PNG output becomes larger
	      than the PNG input.

       -log file
	      Log messages to file.  For safety reasons, file must have the extension .log.
	      This option is deprecated and will be removed eventually. Use shell redirection.

       -out file
	      Write output file to file.  The command line must contain exactly one input file.

       -preserve
	      Preserve file attributes (time stamps, file access rights, etc.) where applicable.

       -quiet, -silent
	      Run in quiet mode.
	      The messages are still written to the log file if the option -log is enabled.

       -simulate
	      Run in simulation mode: perform the trials, but do not create output files.

       -v     Enable the options -verbose and -version.

       -verbose
	      Run in verbose mode.

       -version
	      Show copyright, version and build info.

       --     Stop option switch parsing.

   PNG encoding and optimization options
       -o level
	      Select the optimization level.
	      The optimization level 0 enables a set of optimization operations that require min-
	      imal  effort.  There will be no changes to image attributes like bit depth or color
	      type, and no recompression of existing IDAT datastreams.
	      The optimization level 1 enables a single IDAT compression trial. The trial  chosen
	      is what OptiPNG thinks it's probably the most effective.
	      The  optimization  levels 2 and higher enable multiple IDAT compression trials; the
	      higher the level, the more trials.
	      The behavior and the default value of this option may change across different  pro-
	      gram  versions.  Use  the  option -h to see the details pertaining to your specific
	      version.

       -f filters
	      Select the PNG delta filters.
	      The filters argument is specified as a rangeset (e.g. -f0-5), and the default  fil-
	      ters value depends on the optimization level set by the option -o.
	      The filter values 0, 1, 2, 3 and 4 indicate static filtering, and correspond to the
	      standard PNG filter codes (None, Left, Up, Average and  Paeth,  respectively).  The
	      filter  value  5	indicates  adaptive  filtering,  whose	effect	is defined by the
	      libpng(3) library used by OptiPNG.

       -full  Produce a full report on IDAT.  This option might slow down the trials.

       -i type
	      Select the interlace type (0-1).
	      If the interlace type 0 is selected, the output image shall be non-interlaced (i.e.
	      progressive-scanned).  If  the interlace type 1 is selected, the output image shall
	      be interlaced using the Adam7 method.
	      By default, the output shall have the same interlace type as the input.

       -nb    Do not apply bit depth reduction.

       -nc    Do not apply color type reduction.

       -np    Do not apply palette reduction.

       -nx    Do not apply any lossless image reduction: enable the options -nb, -nc and -np.

       -nz    Do not recode IDAT datastreams.
	      The IDAT optimization operations that do not require recoding (e.g. IDAT chunk con-
	      catenation) are still performed.
	      This option has effect on PNG input files only.

       -zc levels
	      Select the zlib compression levels used in IDAT compression.
	      The  levels argument is specified as a rangeset (e.g. -zc6-9), and the default lev-
	      els value depends on the optimization level set by the option -o.
	      The effect of this option is defined by the zlib(3) library used by OptiPNG.

       -zm levels
	      Select the zlib memory levels used in IDAT compression.
	      The levels argument is specified as a rangeset (e.g. -zm8-9), and the default  lev-
	      els value depends on the optimization level set by the option -o.
	      The effect of this option is defined by the zlib(3) library used by OptiPNG.

       -zs strategies
	      Select the zlib compression strategies used in IDAT compression.
	      The  strategies  argument is specified as a rangeset (e.g. -zs0-3), and the default
	      strategies value depends on the optimization level set by the option -o.
	      The effect of this option is defined by the zlib(3) library used by OptiPNG.

       -zw size
	      Select the zlib window size (32k,16k,8k,4k,2k,1k,512,256) used in IDAT compression.
	      The size argument can be specified either in bytes (e.g. 16384) or kilobytes  (e.g.
	      16k).  The  default size value is set to the lowest window size that yields an IDAT
	      output as big as if yielded by the value 32768.
	      The effect of this option is defined by the zlib(3) library used by OptiPNG.

   Editing options
       -snip  Cut one image out of multi-image, animation or video files.
	      Depending on the input format, this may be either the first or  the  most  relevant
	      (e.g. the largest) image.

       -strip objects
	      Strip metadata objects from a PNG file.
	      PNG  metadata  is the information stored in any ancillary chunk except tRNS.  (tRNS
	      represents the alpha channel, which, even if  ignored  in  rendering,  is  still	a
	      proper image channel in the RGBA color space.)
	      The only option currently supported is -strip all.

   Notes
       Options	may  come  in  any order (except for --), before, after, or alternating with file
       names. Option names are case-insensitive and may be abbreviated to their  shortest  unique
       prefix.

       Some  options  may  have arguments that follow the option name, separated by whitespace or
       the equal sign ('='). If the option argument is a number or a rangeset, the separator  may
       be omitted. For example:

	      -out newfile.png	<=>  -out=newfile.png
	      -o3  <=>	-o 3  <=>  -o=3
	      -f0,3-5  <=>  -f 0,3-5  <=>  -f=0,3-5

       Rangeset arguments are cumulative; e.g.

	      -f0 -f3-5  <=>  -f0,3-5
	      -zs0 -zs1 -zs2-3	<=>  -zs0,1,2,3  <=>  -zs0-3


EXTENDED DESCRIPTION
       The PNG optimization algorithm consists of the following steps:

       1.  Reduce  the	bit  depth, the color type and the color palette of the image.	This step
	   may reduce the size of the uncompressed image, which, indirectly, may reduce the  size
	   of the compressed image (i.e. the size of the output PNG file).

       2.  Run	a  suite of compression methods and strategies and select the compression parame-
	   ters that yield the smallest output file.

       3.  Store all IDAT contents into a single chunk,  eliminating  the  overhead  incurred  by
	   repeated IDAT headers and CRCs.

       4.  Set the zlib window size inside IDAT to a mininum that does not affect the compression
	   ratio, reducing the memory requirements of PNG decoders.

       Not all of the above steps need to be executed. The behavior depends on the  actual  input
       files and user options.

       Step  1	may  be customized via the no-reduce options -nb, -nc, -np and -nx. Step 2 may be
       customized via the -o option, and may be fine-tuned via the options -zc, -zm, -zs and -zw.
       Step 3 is always executed. Step 4 is executed only if a new IDAT is being created, and may
       be fine-tuned via the option -zw.

       Extremely exhaustive searches are not generally expected to yield significant improvements
       in compression ratio, and are recommended to advanced users only.

EXAMPLES
       optipng file.png      # default speed
       optipng -o5 file.png  # slow
       optipng -o7 file.png  # very slow

BUGS
       Lossless  image	reductions  are  not  completely  implemented.	(This does not affect the
       integrity of the output files.)	Here are the missing pieces:

	      - The color palette reductions are implemented only partially.
	      - The bit depth reductions below 8, for grayscale images, are not implemented yet.

       Encoding of images whose total IDAT size exceeds 2GB is not supported.

       TIFF support is limited to uncompressed, PNG-compatible (grayscale, RGB and RGBA) images.

       Metadata is not imported from the external image formats.

       There is no support for pipes or streams.

SEE ALSO
       png(5), libpng(3), zlib(3), pngcrush(1), pngrewrite(1).

STANDARDS
       The files produced by OptiPNG are compliant with PNG-2003:
       Glenn Randers-Pehrson et al.  Portable Network Graphics (PNG) Specification,  Second  Edi-
       tion.
       W3C Recommendation 10 November 2003; ISO/IEC IS 15948:2003 (E).
       http://www.w3.org/TR/PNG/

AUTHOR
       OptiPNG is written and maintained by Cosmin Truta.

       This  manual  page was originally written by Nelson A. de Oliveira for the Debian Project.
       It was later updated by Cosmin Truta, and is now part of the OptiPNG distribution.

OptiPNG version 0.7.4			   2012-Oct-21				       OPTIPNG(1)
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