Provided by: optipng_0.6.4-1_amd64 bug


       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 information. In addition, this program shall perform  a  suite
       of  auxiliary  functions  like  integrity  checks,  metadata  recovery  and  pixmap-to-PNG

       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 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.


   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 operations that require
              minimal 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
              program versions. Use the option -h to see the details pertaining to your  specific

       -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  program  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 execution are not

       -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 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 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.

              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, 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 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.

       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

       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 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, -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.


       optipng file1.png file2.gif file3.tif

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

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


       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.


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


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


       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.