oxipng 9.0.0
Losslessly improve compression of PNG files

Usage: oxipng [OPTIONS] <files>...

Arguments:
  <files>...
          File(s) to compress (use '-' for stdin)

Options:
  -o, --opt <level>
          Set the optimization level preset. The default level 2 is quite fast
          and provides good compression. Lower levels are faster, higher levels
          provide better compression, though with increasingly diminishing
          returns.
          
          0   => --zc 5 --fast               (1 trial, determined heuristically)
          1   => --zc 10 --fast              (1 trial, determined heuristically)
          2   => --zc 11 -f 0,1,6,7 --fast   (4 fast trials, 1 main trial)
          3   => --zc 11 -f 0,7,8,9          (4 trials)
          4   => --zc 12 -f 0,7,8,9          (4 trials)
          5   => --zc 12 -f 0,1,2,5,6,7,8,9  (8 trials)
          6   => --zc 12 -f 0-9              (10 trials)
          max =>                             (stable alias for the max level)
          
          Manually specifying a compression option (zc, f, etc.) will override
          the optimization preset, regardless of the order you write the
          arguments.
          
          [default: 2]

  -r, --recursive
          When directories are given as input, traverse the directory trees and
          optimize all PNG files found (files with “.png” or “.apng” extension).

      --dir <directory>
          Write output file(s) to <directory>. If the directory does not exist,
          it will be created. Note that this will not preserve the directory
          structure of the input files when used with '--recursive'.

      --out <file>
          Write output file to <file>

      --stdout
          Write output to stdout

  -p, --preserve
          Preserve file permissions and timestamps if possible

  -P, --pretend
          Do not write any files, only show compression results

  -s
          Strip safely-removable chunks, same as '--strip safe'

      --strip <mode>
          Strip metadata chunks, where <mode> is one of:
          
          safe    =>  Strip all non-critical chunks, except for the following:
                          cICP, iCCP, sRGB, pHYs, acTL, fcTL, fdAT
          all     =>  Strip all non-critical chunks
          <list>  =>  Strip chunks in the comma-separated list, e.g. 'bKGD,cHRM'
          
          CAUTION: 'all' will convert APNGs to standard PNGs.
          
          Note that 'bKGD', 'sBIT' and 'hIST' will be forcibly stripped if the
          color type or bit depth is changed, regardless of any options set.

      --keep <list>
          Strip all metadata except in the comma-separated list

  -a, --alpha
          Perform additional optimization on images with an alpha channel, by
          altering the color values of fully transparent pixels. This is
          generally recommended for better compression, but take care as this is
          technically a lossy transformation and may be unsuitable for some
          applications.

  -i, --interlace <type>
          Set the PNG interlacing type, where <type> is one of:
          
          0     =>  Remove interlacing from all images that are processed
          1     =>  Apply Adam7 interlacing on all images that are processed
          keep  =>  Keep the existing interlacing type of each image
          
          Note that interlacing can add 25-50% to the size of an optimized
          image. Only use it if you believe the benefits outweigh the costs for
          your use case.
          
          [default: 0]

      --scale16
          Forcibly reduce 16-bit images to 8-bit. Reduction is performed by
          scaling the values, such that e.g. 0x00FF is reduced to 0x01 rather
          than 0x00.

  -v, --verbose...
          Run in verbose mode (use twice to increase verbosity)

  -q, --quiet
          Run in quiet mode

  -f, --filters <list>
          Peform compression trials with each of the given filter types. You can
          specify a comma-separated list, or a range of values. E.g. '-f 0-3' is
          the same as '-f 0,1,2,3'.
          
          PNG delta filters (apply the same filter to every line)
              0  =>  None      (recommended to always include this filter)
              1  =>  Sub
              2  =>  Up
              3  =>  Average
              4  =>  Paeth
          Heuristic strategies (try to find the best delta filter for each line)
              5  =>  MinSum    Minimum sum of absolute differences
              6  =>  Entropy   Highest Shannon entropy
              7  =>  Bigrams   Lowest count of distinct bigrams
              8  =>  BigEnt    Highest Shannon entropy of bigrams
              9  =>  Brute     Smallest compressed size (slow)
          
          The default value depends on the optimization level preset.

      --fast
          Perform a fast compression evaluation of each enabled filter, followed
          by a single main compression trial of the best result. Recommended
          if you have more filters enabled than CPU cores.

      --zc <level>
          Deflate compression level (1-12) for main compression trials. The
          levels here are defined by the libdeflate compression library.
          
          The default value depends on the optimization level preset.

      --nb
          Do not change bit depth

      --nc
          Do not change color type

      --np
          Do not change color palette

      --ng
          Do not change to or from grayscale

      --nx
          Do not perform any transformations and do not deinterlace by default.

      --nz
          Do not recompress IDAT unless required due to transformations.
          Recompression of other compressed chunks (such as iCCP) will also be
          disabled. Note that the combination of '--nx' and '--nz' will fully
          disable all optimization.

      --fix
          Do not perform checksum validation of PNG chunks. This may allow some
          files with errors to be processed successfully.

      --force
          Write the output even if it is larger than the input

  -Z, --zopfli
          Use the much slower but stronger Zopfli compressor for main
          compression trials. Recommended use is with '-o max' and '--fast'.

      --timeout <secs>
          Maximum amount of time, in seconds, to spend on optimizations. Oxipng
          will check the timeout before each transformation or compression
          trial, and will stop trying to optimize the file if the timeout is
          exceeded. Note that this does not cut short any operations that are
          already in progress, so it is currently of limited effectiveness for
          large files with high compression levels.

  -t, --threads <num>
          Set number of threads to use [default: num CPU cores]

  -h, --help
          Print help (see a summary with '-h')

  -V, --version
          Print version
