OPTIPNG(1)                                                          OPTIPNG(1)

NAME
       OptiPNG  -  Advanced optimization program for Portable Network Graphics
       (PNG)

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

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

       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 it is in PNG format:

              Attempt  to optimize the given file in-place. If optimization is
              successful, or if the option -force is in  effect,  replace  the
              original  file  with its optimized version. The original file is
              backed up if the option -keep is in effect.

       - If it is in an external format:

              Create an optimized PNG version of the given  file.  The  output
              file  name  is composed from the original file name and the .png
              extension.

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

       -o level
              Select the optimization level.
              The optimization level 0 enables a set  of  optimization  opera-
              tions  that  require minimal effort. There will be no changes to
              image attributes like bit depth or color type, and no recompres-
              sion 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 com-
              pression trials; the higher the level, the more trials.
              The behavior and the default value of  this  option  may  change
              across  different program versions. Use the option -h to see the
              details pertaining to your specific version.

       -dir directory
              Write output file(s) 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 generally guaranteed. The pro-
              gram may even increase the file size,  e.g.,  by  reconstructing
              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.

       -keep  Keep a backup of the modified file(s).
              The  files that use the backup names prior to the program execu-
              tion are not overwritten.

       -log file
              Log messages to file.  For safety reasons, file  must  have  the
              extension .log.

       -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 Run in quiet mode.
              These  messages  are still written to the log file if the option
              -log is in effect.

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

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

       -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
       -f filters
              Select the PNG delta filters.
              The filters argument is specified as a  rangeset  (e.g.  -f0-5),
              and  the default filters 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 concatenation) 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 levels 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 levels 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 opti-
              mization 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.

   Notes
       Options may come in any order (except for --), before, after, or alter-
       nating  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 num-
       ber 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 parameters that yield the smallest output file.

       3.  Store all IDAT contents into a single chunk, eliminating the  over-
           head 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  sig-
       nificant  improvements  in  compression  ratio,  and are recommended to
       advanced users only.

EXAMPLES
       optipng file1.png file2.gif file3.tif

       optipng -o5 file1.png file2.gif file3.tif

       optipng -i1 -o7 -v -full -sim experiment.png

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.

       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)  Specifi-
       cation, Second Edition.
       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 0.6.4            2010-March-14                      OPTIPNG(1)
