Generaloptions-?, -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.
-dirdirectory
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 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.
-logfile
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.
-outfile
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.
PNGencodingandoptimizationoptions-olevel
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 OptiPNGthinks 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 version.
-ffilters
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.
-itype
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.
-zclevels
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.
-zmlevels
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.
-zsstrategies
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.
-zwsize
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.
Editingoptions-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.
-stripobjects
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 -stripall.
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 <=> -o3 <=> -o=3-f0,3-5 <=> -f0,3-5 <=> -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
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