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<title>OPTIPNG</title>

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<h1 align="center">OPTIPNG</h1>

<hr>

OptiPNG
&minus; Optimize Portable Network Graphics files

<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>

optipng
[&minus;? | &minus;h | &minus;help]
 
optipng [options...] files...

<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>

The
OptiPNG program shall attempt to optimize PNG
files, i.e. reduce their size to a minimum, without losing
semantic information. In addition, this program shall
perform a suite of auxiliary 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.

<h2>FILES
<a name="FILES"></a>
</h2>

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 TIFF.

OptiPNG
processes each image file given in the command line as
follows:

&minus; If the
image is in PNG format:

Attempts to
optimize the given file in-place. If optimization is
successful, or if the option &minus;force is enabled,
replaces the original file with its optimized version. The
original file is backed up if the option &minus;keep
is enabled.

&minus; If the
image is in an external format:

Creates an
optimized PNG version of the given file. The output file
name is composed from the original file name and the
<tt>.png</tt> extension.

Existing files
are not overwritten, unless the option
&minus;clobber is enabled.

<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>

<h3>General options
<a name="General options"></a>
</h3>

&minus;?,
&minus;h, &minus;help

Show a complete summary of
options.

&minus;backup,
&minus;keep

Keep a backup of the modified
files.

&minus;clobber

Overwrite the existing output
and backup files. 
Under this option, if the option &minus;backup is not
enabled, the old backups of the overwritten files are
deleted.

&minus;dir
directory

Write the output files to
directory.

&minus;fix</td>
<td width="4%"></td>
<td width="82%">

Enable error recovery. This option has no effect on
valid input files.</td></tr>
</table>

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.

&minus;force</td>
<td width="1%"></td>
<td width="47%">

Enforce writing of a new output
file. </td>
<td width="35%">
</td></tr>
</table>

This option overrides the
program&rsquo;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.

&minus;log
file

Log messages to file.
For safety reasons, file must have the extension
<tt>.log</tt>. 
This option is deprecated and will be removed eventually.
Use shell redirection.

&minus;out
file

Write output file to
file. The command line must contain exactly one input
file.

&minus;preserve

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

&minus;quiet,
&minus;silent

Run in quiet mode. 
The messages are still written to the log file if the option
&minus;log is enabled.

&minus;simulate

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

&minus;v</td>
<td width="6%"></td>
<td width="53%">

Enable the options &minus;verbose and
&minus;version. </td>
<td width="29%">
</td></tr>
</table>

&minus;verbose

Run in verbose mode.

&minus;version

Show copyright, version and
build info.

&minus;&minus;</td>
<td width="6%"></td>
<td width="35%">

Stop option switch parsing.</td>
<td width="47%">
</td></tr>
</table>

<h3>PNG encoding and optimization options
<a name="PNG encoding and optimization options"></a>
</h3>

&minus;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&rsquo;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
&minus;h to see the details pertaining to your
specific version.

&minus;f
filters

Select the PNG delta filters.
 
The filters argument is specified as a rangeset (e.g.
&minus;f0&minus;5), and the default filters
value depends on the optimization level set by the option
&minus;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.

&minus;full</td>
<td width="3%"></td>
<td width="82%">

Produce a full report on IDAT. This option might slow
down the trials.</td></tr>
</table>

&minus;i type

Select the interlace type
(0&minus;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.

&minus;nb</td>
<td width="5%"></td>
<td width="82%">

Do not apply bit depth reduction.</td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="4%">

&minus;nc</td>
<td width="5%"></td>
<td width="82%">

Do not apply color type reduction.</td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="4%">

&minus;np</td>
<td width="5%"></td>
<td width="82%">

Do not apply palette reduction.</td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="4%">

&minus;nx</td>
<td width="5%"></td>
<td width="82%">

Do not apply any lossless image reduction: enable the
options &minus;nb, &minus;nc and
&minus;np. </td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="4%">

&minus;nz</td>
<td width="5%"></td>
<td width="82%">

Do not recode IDAT datastreams.</td></tr>
</table>

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.

&minus;zc
levels

Select the zlib compression
levels used in IDAT compression. 
The levels argument is specified as a rangeset (e.g.
&minus;zc6&minus;9), and the default levels
value depends on the optimization level set by the option
&minus;o. 
The effect of this option is defined by the zlib(3)
library used by OptiPNG.

&minus;zm
levels

Select the zlib memory levels
used in IDAT compression. 
The levels argument is specified as a rangeset (e.g.
&minus;zm8&minus;9), and the default levels
value depends on the optimization level set by the option
&minus;o. 
The effect of this option is defined by the zlib(3)
library used by OptiPNG.

&minus;zs
strategies

Select the zlib compression
strategies used in IDAT compression. 
The strategies argument is specified as a rangeset
(e.g. &minus;zs0&minus;3), and the default
strategies value depends on the optimization level
set by the option &minus;o. 
The effect of this option is defined by the zlib(3)
library used by OptiPNG.

&minus;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.

<h3>Editing options
<a name="Editing options"></a>
</h3>

&minus;snip</td>
<td width="3%"></td>
<td width="76%">

Cut one image out of
multi-image, animation or video files.</td>
<td width="6%">
</td></tr>
</table>

Depending on the input format,
this may be either the first or the most relevant (e.g. the
largest) image.

&minus;strip
objects

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 &minus;strip
all.

<h3>Notes
<a name="Notes"></a>
</h3>

Options may come
in any order (except for &minus;&minus;), 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 (&rsquo;=&rsquo;). If
the option argument is a number or a rangeset, the separator
may be omitted. For example:

&minus;out
<tt>newfile.png &nbsp;</tt>&lt;=&gt;
&nbsp;&minus;out=<tt>newfile.png</tt> 
&minus;o3 &nbsp;&lt;=&gt; &nbsp;&minus;o 3
&nbsp;&lt;=&gt; &nbsp;&minus;o=3 
&minus;f0,3&minus;5 &nbsp;&lt;=&gt; &nbsp;&minus;f
0,3&minus;5 &nbsp;&lt;=&gt;
&nbsp;&minus;f=0,3&minus;5

Rangeset
arguments are cumulative; e.g.

&minus;f0
&minus;f3&minus;5 &nbsp;&lt;=&gt;
&nbsp;&minus;f0,3&minus;5 
&minus;zs0 &minus;zs1 &minus;zs2&minus;3 &nbsp;&lt;=&gt;
&nbsp;&minus;zs0,1,2,3 &nbsp;&lt;=&gt;
&nbsp;&minus;zs0&minus;3

<h2>EXTENDED DESCRIPTION
<a name="EXTENDED DESCRIPTION"></a>
</h2>

The PNG
optimization algorithm consists of the following steps:

1.</td>
<td width="2%"></td>
<td width="86%">

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). </td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="3%">

2.</td>
<td width="2%"></td>
<td width="86%">

Run a suite of compression methods and strategies and
select the compression parameters that yield the smallest
output file.</td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="3%">

3.</td>
<td width="2%"></td>
<td width="86%">

Store all IDAT contents into a single chunk, eliminating
the overhead incurred by repeated IDAT headers and CRCs.</td></tr>
<tr valign="top" align="left">
<td width="9%"></td>
<td width="3%">

4.</td>
<td width="2%"></td>
<td width="86%">

Set the zlib window size inside IDAT to a mininum that
does not affect the compression ratio, reducing the memory
requirements of PNG decoders.</td></tr>
</table>

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 &minus;nb,
&minus;nc, &minus;np and &minus;nx.
Step 2 may be customized via the &minus;o option, and
may be fine-tuned via the options &minus;zc,
&minus;zm, &minus;zs and &minus;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
&minus;zw.

Extremely
exhaustive searches are not generally expected to yield
significant improvements in compression ratio, and are
recommended to advanced users only.

<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>

<tt>optipng
file.png &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt># default speed
<tt> 
optipng -o5 file.png &nbsp;</tt># slow <tt> 
optipng -o7 file.png &nbsp;</tt># very slow

Lossless image
reductions are not completely implemented. (This does
not affect the integrity of the output files.) Here
are the missing pieces:

&minus; The
color palette reductions are implemented only partially.
 
&minus; The bit depth reductions below 8, for grayscale
images, are not implemented yet.

Encoding of
images whose total IDAT size exceeds 2GB is not
supported.

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, streams, extended file attributes or
access control lists.

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

<h2>STANDARDS
<a name="STANDARDS"></a>
</h2>

The files
produced by OptiPNG are compliant with
PNG&minus;2003: 
Glenn Randers-Pehrson et al. Portable Network Graphics
(PNG) Specification, Second Edition. 
W3C Recommendation 10 November 2003; ISO/IEC IS 15948:2003
(E). <tt> 
http://www.w3.org/TR/PNG/</tt>

<h2>AUTHOR
<a name="AUTHOR"></a>
</h2>

<tt>OptiPNG</tt>
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.
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