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.
              Use -o0 to disable IDAT recompression trials. This option has no
              effect on non-PNG input files.
              Use -o1 to enable a single IDAT recompression trial.
              Use  a higher level to enable more trials (the higher the level,
              the more trials).
              The behavior and the default value of  this  option  may  change
              across  different  program  versions.  Use  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.
              Use  this option to override 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).
              Use -i0 to produce a non-interlaced output.
              Use -i1 to produce an interlaced (Adam7) output.
              By default, the output will 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.

       -nz    Do not perform IDAT recompression (also disable reductions).

       -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
              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  and  -np.
       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;  for
       example, even though IDAT recompression is disabled under -o0, all IDAT
       chunks from the input are concatenated into a single IDAT chunk in  the
       output. 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 -log experiment.log

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).

       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 0.6.3             2009-May-18                       OPTIPNG(1)
