1OPTIPNG(1) General Commands Manual OPTIPNG(1)
2
6 OptiPNG - Advanced optimization program for Portable Network Graphics
7 (PNG)
8
11 optipng [-? | -h | -help]
12 optipng [options...] files...
13
16 The OptiPNG program shall attempt to optimize PNG files, i.e. reduce
17 their size to a minimum, without losing any information. In addition,
18 this program shall perform a suite of auxiliary functions like
19 integrity checks, metadata recovery and pixmap-to-PNG conversion.
20 The optimization attempts are not guaranteed to succeed. Valid PNG
22 files that cannot be optimized by this program are normally left
23 intact; their size will not grow. The user may request to override this
24 default behavior.
25
28 The input files are raster image files encoded either in PNG format
29 (the native format), or in an external format. The currently supported
30 external formats are GIF, BMP, PNM and TIFF.
31 OptiPNG processes each image file given in the command line as follows:
33 - If it is in PNG format:
35 Attempt to optimize the given file in-place. If optimization is
37 successful, or if the option -force is in effect, replace the
38 original file with its optimized version. The original file is
39 backed up if the option -keep is in effect.
40 - If it is in an external format:
42 Create an optimized PNG version of the given file. The output
44 file name is composed from the original file name and the .png
45 extension.
46
49 General options
50 -?, -h, -help
51 Show a complete summary of options.
52 -o level
54 Select the optimization level.
55 The optimization level 0 enables a set of optimization opera‐
56 tions that require minimal effort. There will be no changes to
57 image attributes like bit depth or color type, and no recompres‐
58 sion of existing IDAT datastreams.
59 The optimization level 1 enables a single IDAT compression
60 trial. The trial chosen is what OptiPNG thinks it's probably the
61 most effective.
62 The optimization levels 2 and higher enable multiple IDAT com‐
63 pression trials; the higher the level, the more trials.
64 The behavior and the default value of this option may change
65 across different program versions. Use the option -h to see the
66 details pertaining to your specific version.
67 -dir directory
69 Write output file(s) to directory.
70 -fix Enable error recovery. This option has no effect on valid input
72 files.
73 The program will spend a reasonable amount of effort to recover
74 as much data as possible, without increasing the output file
75 size, but the success cannot be generally guaranteed. The pro‐
76 gram may even increase the file size, e.g., by reconstructing
77 missing critical data. Under this option, integrity shall take
78 precedence over file size.
79 When this option is not used, the invalid input files are left
80 unprocessed.
81 -force Enforce writing of a new output file.
83 This option overrides the program's decision not to write such
84 file, e.g. when the PNG input is digitally signed (using dSIG),
85 or when the PNG output becomes larger than the PNG input.
86 -keep Keep a backup of the modified file(s).
88 The files that use the backup names prior to the program execu‐
89 tion are not overwritten.
90 -log file
92 Log messages to file. For safety reasons, file must have the
93 extension .log.
94 -out file
96 Write output file to file. The command line must contain
97 exactly one input file.
98 -preserve
100 Preserve file attributes (time stamps, file access rights, etc.)
101 where applicable.
102 -quiet Run in quiet mode.
104 These messages are still written to the log file if the option
105 -log is in effect.
106 -simulate
108 Run in simulation mode: perform the trials, but do not create
109 output files.
110 -snip Cut one image out of multi-image, animation or video file(s).
112 Depending on the input format, this may be either the first or
113 the most relevant (e.g. the largest) image.
114 -v Enable the options -verbose and -version.
116 -verbose
118 Run in verbose mode.
119 -version
121 Show copyright, version and build info.
122 -- Stop option switch parsing.
124 PNG encoding and optimization options
126 -f filters
127 Select the PNG delta filters.
128 The filters argument is specified as a rangeset (e.g. -f0-5),
129 and the default filters value depends on the optimization level
130 set by the option -o.
131 The filter values 0, 1, 2, 3 and 4 indicate static filtering,
132 and correspond to the standard PNG filter codes (None, Left, Up,
133 Average and Paeth, respectively). The filter value 5 indicates
134 adaptive filtering, whose effect is defined by the libpng(3)
135 library used by OptiPNG.
136 -full Produce a full report on IDAT. This option might slow down the
138 trials.
139 -i type
141 Select the interlace type (0-1).
142 If the interlace type 0 is selected, the output image shall be
143 non-interlaced (i.e. progressive-scanned). If the interlace type
144 1 is selected, the output image shall be interlaced using the
145 Adam7 method.
146 By default, the output shall have the same interlace type as the
147 input.
148 -nb Do not apply bit depth reduction.
150 -nc Do not apply color type reduction.
152 -np Do not apply palette reduction.
154 -nx Do not apply any lossless image reduction: enable the options
156 -nb, -nc and -np.
157 -nz Do not recode IDAT datastreams.
159 The IDAT optimization operations that do not require recoding
160 (e.g. IDAT chunk concatenation) are still performed.
161 This option has effect on PNG input files only.
162 -zc levels
164 Select the zlib compression levels used in IDAT compression.
165 The levels argument is specified as a rangeset (e.g. -zc6-9),
166 and the default levels value depends on the optimization level
167 set by the option -o.
168 The effect of this option is defined by the zlib(3) library used
169 by OptiPNG.
170 -zm levels
172 Select the zlib memory levels used in IDAT compression.
173 The levels argument is specified as a rangeset (e.g. -zm8-9),
174 and the default levels value depends on the optimization level
175 set by the option -o.
176 The effect of this option is defined by the zlib(3) library used
177 by OptiPNG.
178 -zs strategies
180 Select the zlib compression strategies used in IDAT compression.
181 The strategies argument is specified as a rangeset (e.g.
182 -zs0-3), and the default strategies value depends on the opti‐
183 mization level set by the option -o.
184 The effect of this option is defined by the zlib(3) library used
185 by OptiPNG.
186 -zw size
188 Select the zlib window size (32k,16k,8k,4k,2k,1k,512,256) used
189 in IDAT compression.
190 The size argument can be specified either in bytes (e.g. 16384)
191 or kilobytes (e.g. 16k). The default size value is set to the
192 lowest window size that yields an IDAT output as big as if
193 yielded by the value 32768.
194 The effect of this option is defined by the zlib(3) library used
195 by OptiPNG.
196 Notes
198 Options may come in any order (except for --), before, after, or alter‐
199 nating with file names. Option names are case-insensitive and may be
200 abbreviated to their shortest unique prefix.
201 Some options may have arguments that follow the option name, separated
203 by whitespace or the equal sign ('='). If the option argument is a num‐
204 ber or a rangeset, the separator may be omitted. For example:
205 -out newfile.png <=> -out=newfile.png
207 -o3 <=> -o 3 <=> -o=3
208 -f0,3-5 <=> -f 0,3-5 <=> -f=0,3-5
209 Rangeset arguments are cumulative; e.g.
211 -f0 -f3-5 <=> -f0,3-5
213 -zs0 -zs1 -zs2-3 <=> -zs0,1,2,3 <=> -zs0-3
214
217 The PNG optimization algorithm consists of the following steps:
218 1. Reduce the bit depth, the color type and the color palette of the
220 image. This step may reduce the size of the uncompressed image,
221 which, indirectly, may reduce the size of the compressed image
222 (i.e. the size of the output PNG file).
223 2. Run a suite of compression methods and strategies and select the
225 compression parameters that yield the smallest output file.
226 3. Store all IDAT contents into a single chunk, eliminating the over‐
228 head incurred by repeated IDAT headers and CRCs.
229 4. Set the zlib window size inside IDAT to a mininum that does not
231 affect the compression ratio, reducing the memory requirements of
232 PNG decoders.
233 Not all of the above steps need to be executed. The behavior depends on
235 the actual input files and user options.
236 Step 1 may be customized via the no-reduce options -nb, -nc, -np and
238 -nx. Step 2 may be customized via the -o option, and may be fine-tuned
239 via the options -zc, -zm, -zs and -zw. Step 3 is always executed. Step
240 4 is executed only if a new IDAT is being created, and may be fine-
241 tuned via the option -zw.
242 Extremely exhaustive searches are not generally expected to yield sig‐
244 nificant improvements in compression ratio, and are recommended to
245 advanced users only.
246
249 optipng file1.png file2.gif file3.tif
250 optipng -o5 file1.png file2.gif file3.tif
252 optipng -i1 -o7 -v -full -sim experiment.png
254
257 Lossless image reductions are not completely implemented. (This does
258 NOT affect the integrity of the output files.) Here are the missing
259 pieces:
260 - The color palette reductions are implemented only partially.
262 - The bit depth reductions below 8, for grayscale images, are
263 not implemented yet.
264 TIFF support is limited to uncompressed, PNG-compatible (grayscale, RGB
266 and RGBA) images.
267 Metadata is not imported from the external image formats.
269 There is no support for pipes or streams.
271
274 png(5), libpng(3), zlib(3), pngcrush(1), pngrewrite(1).
275
278 The files produced by OptiPNG are compliant with PNG-2003:
279 Glenn Randers-Pehrson et al. Portable Network Graphics (PNG) Specifi‐
280 cation, Second Edition.
281 W3C Recommendation 10 November 2003; ISO/IEC IS 15948:2003 (E).
282 http://www.w3.org/TR/PNG/
283
286 OptiPNG is written and maintained by Cosmin Truta.
287 This manual page was originally written by Nelson A. de Oliveira for
289 the Debian Project. It was later updated by Cosmin Truta, and is now
290 part of the OptiPNG distribution.
291OptiPNG version 0.6.4 2010-March-14 OPTIPNG(1)