| OPTIPNG(1) OPTIPNG(1) |
| |
| NAME |
| OptiPNG - Optimize Portable Network Graphics files |
| |
| SYNOPSIS |
| optipng [-? | -h | -help] |
| optipng [options...] files... |
| |
| DESCRIPTION |
| The OptiPNG program shall attempt to optimize PNG files, i.e. reduce |
| their size to a minimum, without losing semantic information. In addi- |
| tion, 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. |
| |
| FILES |
| 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: |
| |
| - If the image is in PNG format: |
| |
| Attempts to optimize the given file in-place. If optimization is |
| successful, or if the option -force is enabled, replaces the |
| original file with its optimized version. The original file is |
| backed up if the option -keep is enabled. |
| |
| - 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 .png |
| extension. |
| |
| Existing files are not overwritten, unless the option -clobber is |
| enabled. |
| |
| OPTIONS |
| General options |
| -?, -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. |
| |
| -dir directory |
| 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 pro- |
| gram 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. |
| |
| -log file |
| 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. |
| |
| -out file |
| 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. |
| |
| PNG encoding and optimization options |
| -o level |
| Select the optimization level. |
| The optimization level 0 enables a set of optimization opera- |
| tions that require minimal effort. There will be no changes to |
| image attributes like bit depth or color type, and no recompres- |
| sion 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 com- |
| pression 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. |
| |
| -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 opti- |
| mization 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. |
| |
| Editing options |
| -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. |
| |
| -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 -strip all. |
| |
| Notes |
| Options may come in any order (except for --), before, after, or alter- |
| nating 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 num- |
| ber 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 |
| |
| EXTENDED DESCRIPTION |
| 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 over- |
| head 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 sig- |
| nificant improvements in compression ratio, and are recommended to |
| advanced users only. |
| |
| EXAMPLES |
| optipng file.png # default speed |
| optipng -o5 file.png # slow |
| optipng -o7 file.png # very slow |
| |
| 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. |
| |
| 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 or streams. |
| |
| SEE ALSO |
| png(5), libpng(3), zlib(3), pngcrush(1), pngrewrite(1). |
| |
| STANDARDS |
| The files produced by OptiPNG are compliant with PNG-2003: |
| Glenn Randers-Pehrson et al. Portable Network Graphics (PNG) Specifi- |
| cation, Second Edition. |
| W3C Recommendation 10 November 2003; ISO/IEC IS 15948:2003 (E). |
| http://www.w3.org/TR/PNG/ |
| |
| 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. |
| |
| OptiPNG version 0.7.4 2012-Oct-21 OPTIPNG(1) |
