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optipng

NAME

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

SYNOPSIS

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

DESCRIPTION

OptiPNG is a PNG optimizer that recompresses image files to a smaller size without losing any information. In addition, this program performs a suite of useful functions like integrity checks, meta-data recovery and pixmap-to-PNG conversion.

FILES

The input files are image files of following types:

- Native format: PNG.

- External pixmap formats (currently supported: GIF, BMP, PNM and TIFF).

OptiPNG processes each input file as follows:

- If it is a PNG file:

If it is possible to create an optimized version of the given PNG file, the optimized file replaces the original one. The original file can be backed up, at the user's option.

- Otherwise (i.e. if it is an external pixmap format):

An optimized PNG version of the given image file is created. The output file name is created from the original file name and the .png extension.

For example:

optipng file1.png file2.gif

will create an optimized file1.png and an optimized file2.png. (The original file1.png is replaced by the optimized one; the original file2.gif is left intact.)

OPTIONS

Basic options

-?, -h, -help

Show a complete summary of options.

-o level

Select the optimization level.
Use -o0 to disable IDAT recompression trials.
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 user option may change across different program versions. Use option -h to see the details pertaining to your specific version.

-i type

Select the interlace type (0-1).
Use -i0 to produce a non-interlaced output.
Use -i1 to produce an interlaced (Adam7) output.
If this option is not used, the output will have the same interlace type as the input.

-k, -keep

Keep a backup of the modified file(s).
The files that use the backup names prior to the program execution are not overwritten.

-q, -quiet

Run in quiet mode.

-v

Run in verbose mode / Show copyright, version and build info.

Advanced options

-zc levels

Select the zlib compression levels.
The behavior and the default value of this user option may change across different program versions. Use option -h to see the details pertaining to your specific version.

-zm levels

Select the zlib memory levels.
The behavior and the default value of this user option may change across different program versions. Use option -h to see the details pertaining to your specific version.

-zs strategies

Select the zlib compression strategies.
The behavior and the default value of this user option may change across different program versions. Use option -h to see the details pertaining to your specific version.

-zw window size

Select the zlib window size (32k,16k,8k,4k,2k,1k,512,256).
The window size can be specified either in bytes (e.g. 16384) or kilobytes (e.g. 16k).

-f filters

Select the PNG delta filters.
The behavior and the default value of this user option may change across different program versions. The filter values 0, 1, 2, 3, 4 correspond to the PNG standard filters (None, Left, Up, Average and Paeth, respectively). The other values are used to specify adaptive filtering. Use option -h to see the details pertaining to your specific version.

-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).

-fix

Enable error recovery.

-force

Write a new output file, even if it is larger than the input file.

-full

Produce a full report on IDAT. This option might slow down the trials.

-preserve

Preserve file attributes (time stamps, file access rights, etc.) where applicable.

-simulate

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

-out file

Write output file to file. The command line must not contain more than one input file.

-dir directory

Write output file(s) to directory.

-log file

Log messages to file. For safety reasons, file must have the extension .log.

--

Stop option switch parsing.

Notes

The option names are case-insensitive and can be abbreviated. Any abbreviation must uniquely identify the full option name and must be no shorter than two letters, unless one letter is explicitly permitted. For example, -quiet can be abbreviated as -q or -qu (because -q is explicitly mentioned in the list of possible options), while -preserve can be abbreviated as -pr but not as -p.

Some options may have arguments that follow the option name, with or without a whitespace used as a separator; e.g.

optipng -i1 -o3 file.png <=> optipng -i 1 -o 3 file.png

Range arguments are cumulative; e.g.

-f0 -f3-5 <=> -f0,3-5
-zs0 -zs1 -zs2-3 <=> -zs0,1,2,3 <=> -zs0-3

The zlib window size is automatically set to a minimum that does not affect the compression ratio.

The output files will have all IDAT in a single chunk, even if no recompression is performed.

Extremely exhaustive searches are not generally recommended.

EXAMPLES

optipng file.png

optipng -o5 file.png

optipng -o7 file.png

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.
- The gray(alpha)-to-palette reductions are not implemented yet.

BMP support is limited to uncompressed images.

TIFF support is limited to uncompressed, PNG-compatible (grayscale, RGB and RGBA) images.

Metadata is not imported from the external image formats.

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.