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optipng - Advanced PNG optimizer…  more info»


OPTIPNG(1)                                                OPTIPNG(1)

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

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

       The OptiPNG program shall attempt to optimize PNG files, i.e.
       reduce  their  size to a minimum, without losing any informa‐
       tion. In addition, this program shall perform a suite of aux‐
       iliary 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.

       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

       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 opti‐
              mization 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.

   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 ver‐

       -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  increas‐
              ing  the  output  file size, but the success cannot be
              generally guaranteed. The program  may  even  increase
              the  file size, e.g., by reconstructing missing criti‐
              cal 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 digi‐
              tally 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 pro‐
              gram execution 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 con‐
              tain exactly one input file.

              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.

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

       -snip  Cut  one  image out of multi-image, animation or video
              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.

              Run in verbose mode.

              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, respec‐
              tively). The filter value 5 indicates adaptive filter‐
              ing,  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 reduc‐

       -zc levels
              Select  the  zlib compression levels used in IDAT com‐
              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 compres‐
              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
              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
              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 compres‐
              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.

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

       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

       The PNG optimization  algorithm  consists  of  the  following

       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, eliminat‐
              ing the overhead incurred by repeated IDAT headers and

       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 recompres‐
       sion 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 significant improvements in compression ratio, and  are
       recommended to advanced users only.

       optipng file1.png file2.gif file3.tif

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

       optipng  -i1  -o7  -v  -full -sim experiment.png -log experi‐

       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
              -  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.

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

       Glenn Randers-Pehrson et al.  Portable Network Graphics (PNG)
       Specification, Second Edition.
       W3C Recommendation 10 November 2003;  ISO/IEC  IS  15948:2003

       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 Cos‐
       min Truta, and is now part of the OptiPNG distribution.

OptiPNG version 0.6.3        2009-May-18                  OPTIPNG(1)
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