1Pnmtopng User Manual(0) Pnmtopng User Manual(0)
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6 pnmtopng - convert a PNM image to PNG
7
10 pnmtopng [-verbose] [-downscale] [-interlace] [-alpha=file] [-transpar‐
11 ent=[=]color] [-background=color] [-palette=palettefile] [-gamma=value]
12 [-hist] [-text=file] [-ztxt=file] [-rgb='wx wy
13 rx ry gx gy bx by'] [-size='x y unit'] [-srgbintent=intent] [-mod‐
14 time='[yy]yy-mm-dd
15 hh:mm:ss'] [-nofilter] [-sub] [-up] [-avg] [-paeth] [-compression=n]
16 [-comp_mem_level=n] [-comp_strategy={huffman_only|filtered}]
17 [-comp_method=deflated] [-comp_window_bits=n] [-comp_buffer_size=n]
18 [-force] [-libversion] [pnmfile]
19
23 Obsolete options:
24 [-filter n]
26 Options available only in older versions:
28 [-chroma wx wy rx ry gx gy bx by] [-phys x y unit] [-time [yy]yy-mm-dd
30 hh:mm:ss]
31 Minimum unique abbreviation of option is acceptable. You may use dou‐
33 ble hyphens instead of single hyphen to denote options. You may use
34 white space in place of the equals sign to separate an option name from
35 its value.
36
39 This program is part of Netpbm(1).
40 pnmtopng reads a PNM image as input and produces a PNG image as output.
42 Color component values in PNG files are either eight or sixteen bits
44 wide, so pnmtopng will automatically scale colors to have a maxval of
45 255 or 65535.
46 For a grayscale image, pnmtopng produces a PNG bit depth 1, 2, 4, 8 or
48 16. When the input image has a small maxval, the output PNG image has
49 a correspondingly small bit depth. But in mapping the PNM maxval to
50 the PNG maxval (which is by definition the maximum value that can be
51 represented in the number of bits), a fair amount of distortion happens
52 with these low maxvals. For example, with a PNM maxval of 5 and a PNG
53 maxval of 7, the input sample 2 becomes the output sample 3. The input
54 brightness is 2/5 = .40, while the output brightness is 3/7 = .43.
55 Note that this is not a problem if you view the maxval as a precision,
56 because in .4 and .43 are identical within the precision implied by
57 maxval 5. Indeed, if you convert this PNG back to a maxval 5 PGM, the
58 pixel's value will again be 2, exactly as it was originally. But if
59 you need precisely the same colors in the output PNG as in the input
60 PNM, make sure your input PNM has a maxval which is a power of two
61 minus one. If you can't do that, then convert it with pamdepth to
62 something with a large maxval that is a power of two minus one (255 and
63 65535 are good choices) to minimize the error.
64
68 pnmtopng changed in Netpbm 10.30 (October 2005) to use the standard
69 Netpbm command line syntax. Before that, you could not use double
70 hyphens to denote an option and could not use an equal sign to separate
71 an option name from its value. And the options had to come before the
72 non-option program arguments.
73 Furthermore, the options -chroma, -phys, and -time were replaced by
75 -rgb, -size, and -modtime, respectively. The only difference, taking
76 -phys/-size as an example, is that -phys takes multiple program argu‐
77 ments as the option argument, whereas -size takes a single program
78 argument which is composed of multiple words. E.g. The old shell com‐
79 mand
80 pnmtopng -phys 800 800 0 input.pnm >output.png
82 is equivalent to the new shell command
84 pnmtopng -size "800 800 0" input.pnm >output.png
86 If you're writing a program that needs to work with both new and old
88 pnmtopng, have it first try with the new syntax, and if it fails with
89 "unrecognized option," fall back to the old syntax.
90 -verbose
94 Display the format of the output file.
95 -downscale
97 Enables scaling of maxvalues of more then 65535 to 16 bit.
98 Since
99 this means loss of image data, pnmtopng does not do it by
100 default..TP -interlace
101 Creates an interlaced PNG file (Adam7).
102 -alpha=filename
104 This specifies the transparency (alpha) channel of the image.
105 You supply the transparency channel as a standard PGM trans‐
106 parency mask (see the PGM(1) specification. pnmtopng does not
107 necessarily represents the transparency information as a trans‐
108 parency channel in the PNG format. If it can represent the
109 transparency information through a palette, it will do so in
110 order to make a smaller PNG file. pnmtopng even sorts the pal‐
111 ette so it can omit the opaque colors from the transparency part
112 of the palette and save space for the palette.
113 -transparent=color
116 pnmtopng marks the specified color as transparent in the PNG
117 image.
118 Specify the color (color) as described for the argument of the
120 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ . E.g.
121 red or rgb:ff/00/0d. If the color you specify is not present in
122 the image, pnmtopng selects instead the color in the image that
123 is closest to the one you specify. Closeness is measured as a
124 Cartesian distance between colors in RGB space. If multiple
125 colors are equidistant, pnmtopng chooses one of them arbitrar‐
126 ily.
127 However, if you prefix your color specification with "=", e.g.
129 -transparent =red
131 only the exact color you specify will be transparent. If that
133 color does not appear in the image, there will be no trans‐
134 parency. pnmtopng issues an information message when this is
135 the case.
136 -background=color
139 Causes pnmtopng to create a background color chunk in the PNG
140 output which can be used for subsequent transparency channel or
141 transparent color conversions. Specify color the same as for
142 -transparent.
143 -palette=palettefile
146 This option specifies a palette to use in the PNG. It forces
147 pnmtopng to create the paletted (colormapped) variety of PNG --
148 if that isn't possible, pnmtopng fails. If the palette you
149 specify doesn't contain exactly the colors in the image, pnm‐
150 topng fails. Since pnmtopng will automatically generate a
151 paletted PNG, with a correct palette, when appropriate, the only
152 reason you would specify the -palette option is if you care in
153 what order the colors appear in the palette. The PNG palette
154 has colors in the same order as the palette you specify.
155 You specify the palette by naming a PPM file that has one pixel
157 for each color in the palette.
158 Alternatively, consider the case that have a palette and you
160 want to make sure your PNG contains only colors from the pal‐
161 ette, approximating if necessary. You don't care what indexes
162 the PNG uses internally for the colors (i.e. the order of the
163 PNG palette). In this case, you don't need -palette. Pass the
164 Netpbm input image and your palette PPM through pnmremap.
165 Though you might think it would, using -palette in this case
166 wouldn't even save pnmtopng any work.
167 -gamma=value
170 Causes pnmtopng to create a gAMA chunk. This information helps
171 describe how the color values in the PNG must be interpreted.
172 Without the gAMA chunk, whatever interprets the PNG must get
173 this information separately (or just assume something standard).
174 If your input is a true PPM or PGM image, you should specify
175 -gamma=.52. But sometimes people generate images which are
176 ostensibly PPM except the image uses a different gamma transfer
177 function than the one specified for PPM. A common case of this
178 is when the image is created by simple hardware that doesn't
179 have digital computational ability. Also, some simple programs
180 that generate images from scratch do it with a gamma transfer in
181 which the gamma value is 1.0.
182 -hist Use this parameter to create a chunk that specifies the fre‐
185 quency (or histogram) of the colors in the image.
186 -text=filename
189 This option lets you include arbitrary text strings in the PNG
190 output, as tEXt chunks.
191 filename is the name of a file that contains your text strings.
193 The output contains a distinct tEXt chunk for each entry in the
195 file.
196 Here is an example of a text string file:
198 Title PNG file
200 Author John Doe
201 Description how to include a text chunk
202 PNG file
203 "Creation Date" 2015-may-11
204 Software pamtopng
205 The file is divided into entries, each entry comprising consecu‐
207 tive lines of text. The first line of an entry starts in the
208 first column (i.e. the first column is not white space) and
209 every other line has white space in the first column. The first
210 entry starts in the first line, so it is not valid for the first
211 line of the file to have white space in its first column.
212 The first word in an entry is the key of the text string (e.g.
214 'Title'). It begins in column one of the line and continues up
215 to, but not including, the first delimiter character or the end
216 of the line, whichever is first. You can enclose the key in
217 double quotes in which case the key can consists of multiple
218 words. The quotes are not part of the key. The text string per
219 se begins after the key and any delimiter characters after it,
220 plus the text in subsequent continuation lines.
221 There is no limit on the length of a file line or entry or key
223 or text string. There is no limit on the number of entries.
224 -ztxt=filename
227 The same as -text, except the text string is compressed in the
228 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks,
229 unless the key for the text string starts with 'A' or 'T'. This
230 odd exception exists for backward compatibility; we don't know
231 why the program was originally designed this way, except that
232 the distinction was meant to roughly identify the keys 'Author'
233 and 'Title'.
234 -rgb=chroma_list
238 This option specifies how red, green, and blue component values
239 of a pixel specify a particular color, by telling the chromatic‐
240 ities of those 3 primary illuminants and of white (i.e. full
241 strength of all three).
242 The chroma_list value is a blank-separated list of 8 floating
244 point decimal numbers. The CIE-1931 X and Y chromaticities (in
245 that order) of each of white, red, green, and blue, in that
246 order.
247 This information goes into the PNG's cHRM chunk.
249 In a shell command, make sure you use quotation marks so that
251 the blanks in chroma_list don't make the shell see multiple com‐
252 mand arguments.
253 This option was new in Netpbm 10.30 (October 2005). Before
255 that, the option -chroma does the same thing, but with slightly
256 different syntax.
257 -size="x y unit"
260 This option determines the aspect ratio of the individual pixels
261 of your image as well as the physical resolution of it.
262 unit is either 0 or 1. When it is 1, the option specifies the
264 physical resolution of the image in pixels per meter. For exam‐
265 ple, -size="10000 15000 1" means that when someone displays the
266 image, he should make it so that 10,000 pixels horizontally
267 occupy 1 meter and 15,000 pixels vertically occupy one meter.
268 And even if he doesn't take this advice on the overall size of
269 the displayed image, he should at least make it so that each
270 pixel displays as 1.5 times as high as wide.
271 When unit is 0, that means there is no advice on the absolute
273 physical resolution; just on the ratio of horizontal to vertical
274 physical resolution.
275 This information goes into the PNG's pHYS chunk.
277 When you don't specify -size, pnmtopng creates the image with no
279 pHYS chunk, which means square pixels of no absolute resolution.
280 This option was new in Netpbm 10.30 (October 2005). Before
282 that, the option -phys does the same thing, but with slightly
283 different syntax.
284 -srgbintent=intent
287 This asserts that the input is a pseudo-Netpbm image that uses
288 an sRGB color space (unlike true Netpbm) and indicates how you
289 intend for the colors to be rendered. It causes pnmtopng to
290 include an sRGB chunk in the PNG image that specifies that
291 intent, so see the PNG documentation for more information on
292 what this really means.
293 intent is one of:
295 · perceptual
299 · relativecolorimetric
301 · saturation
303 · absolutecolorimetric
305 This option was new in Netpbm 10.71 (June 2015). Before that,
308 pnmtopng never generates an sRGB chunk.
309 -modtime="[yy]yy-mm-dd hh:mm:ss"
312 This option allows you to specify the modification time value to
313 be placed in the PNG output. You can specify the year parameter
314 either as a two digit or four digit value.
315 This option was new in Netpbm 10.30 (October 2005). Before
317 that, the option -time does the same thing, but with slightly
318 different syntax.
319 -filter=n
322 This option is obsolete. Before Netpbm 10.22 (April 2004), this
323 was the only way to specify a row filter. It specifies a single
324 type of row filter, by number, that pnmtopng must use on each
325 row.
326 Use -nofilter, -sub, -up, -avg, and -paeth in current Netpbm.
328 -nofilter
331 -sub
333 -up
335 -avg
337 -paeth Each of these options permits pnmtopng to use one type of row
339 filter. pnmtopng chooses whichever of the permitted filters it
340 finds to be optimal. If you specify none of these options, it
341 is the same as specifying all of them -- pnmtopng uses any row
342 filter type it finds optimal.
343 These options were new with Netpbm 10.22 (April 2004). Before
345 that, you could use the -filter option to specify one permitted
346 row filter type. The default, when you specify no filter
347 options, was the same.
348 -compression=n
351 This option sets set the compression level of the zlib compres‐
352 sion. Select a level from 0 for no compression (maximum speed)
353 to 9 for maximum compression (minimum speed).
354 The default is the default of the zlib library.
356 -comp_mem_level=n
359 This option sets the memory usage level of the zlib compression.
360 Select a level from 1 for minimum memory usage (and minimum
361 speed) to 9 for maximum memory usage (and speed).
362 The default is the default of the zlib library.
364 This option was new in Netpbm 10.30 (October 2005).
366 -comp_strategy={huffman_only|filtered}
369 This options sets the compression strategy of the zlib compres‐
370 sion. See Zlib documentation for information on what these
371 strategies are.
372 The default is the default of the zlib library.
374 This option was new in Netpbm 10.30 (October 2005).
376 -comp_method=deflated
379 This option does nothing. It is here for mathematical complete‐
380 ness and for possible forward compatibility. It theoretically
381 selects the compression method of the zlib compression, but the
382 Z library knows only one method today, so there's nothing to
383 choose.
384 The default is the default of the zlib library.
386 This option was new in Netpbm 10.30 (October 2005).
388 -comp_window_bits=N
391 This option tells how big a window the zlib compression algo‐
392 rithm uses. The value is the base 2 logarithm of the window
393 size in bytes, so 8 means 256 bytes. The value must be from 8
394 to 15 (i.e. 256 bytes to 32K).
395 See Zlib documentation for details on what this window size is.
397 The default is the default of the zlib library.
399 This option was new in Netpbm 10.30 (October 2005).
401 -comp_buffer_size=N
404 This option determines in what size pieces pnmtopng does the
405 zlib compression. One compressed piece goes in each IDAT chunk
406 in the PNG. So the bigger this value, the fewer IDAT chunks
407 your PNG will have. Theoretically, this makes the PNG smaller
408 because 1) you have less per-IDAT-chunk overhead, and 2) the
409 compression algorithm has more data to work with. But in real‐
410 ity, the difference will probably not be noticeable above about
411 8K, which is the default.
412 The value n is the size of the compressed piece (i.e. the com‐
414 pression buffer) in bytes.
415 This option was new in Netpbm 10.30 (October 2005).
417 -force When you specify this, pnmtopng limits its optimizations. The
421 resulting PNG output is as similar to the Netpbm input as possi‐
422 ble. For example, the PNG output will not be paletted and the
423 transparency channel will be represented as a full transparency
424 channel even if the information could be represented more suc‐
425 cinctly with a transparency chunk.
426 -libversion
430 This option causes pnmtopng to display version information about
431 itself and the libraries it uses, in addition to all its normal
432 function. Do not confuse this with the Netpbm common option
433 -version, which causes the program to display version informa‐
434 tion about the Netpbm library and do nothing else.
435 You can't really use this option in a program that invokes pnm‐
437 topng and needs to know which version it is. Its function has
438 changed too much over the history of pnmtopng. The option is
439 good only for human eyes.
440
445 pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)
446 For information on the PNG format, see http://schaik.com/png
448 ⟨http://schaik.com/png⟩ .
449
452 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
453
455 This manual page was generated by the Netpbm tool 'makeman' from HTML
456 source. The master documentation is at
457 http://netpbm.sourceforge.net/doc/pnmtopng.html
459netpbm documentation 09 October 2016 Pnmtopng User Manual(0)