1Pnmtopng User Manual(0) Pnmtopng User Manual(0)
2
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 mi‐
61 nus one. If you can't do that, then convert it with pamdepth to some‐
62 thing 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 Note: Option Syntax of Older Versions
69 pnmtopng changed in Netpbm 10.30 (October 2005) to use the standard
70 Netpbm command line syntax. Before that, you could not use double hy‐
71 phens to denote an option and could not use an equal sign to separate
72 an option name from its value. And the options had to come before the
73 non-option program arguments.
74 Furthermore, the options -chroma, -phys, and -time were replaced by
76 -rgb, -size, and -modtime, respectively. The only difference, taking
77 -phys/-size as an example, is that -phys takes multiple program argu‐
78 ments as the option argument, whereas -size takes a single program ar‐
79 gument which is composed of multiple words. E.g. The old shell com‐
80 mand
81 pnmtopng -phys 800 800 0 input.pnm > output.png
83 is equivalent to the new shell command
86 pnmtopng -size "800 800 0" input.pnm > output.png
88 If you're writing a program that needs to work with both new and old ,
91 have it first try with the new syntax, and if it fails with "unrecog‐
92 nized option," fall back to the old syntax.
93 Current Options
96 In addition to the options common to all programs based on libnetpbm
97 (most notably -quiet, see
98 Common Options ⟨index.html#commonoptions⟩ ), pnmtopng recognizes the
99 following command line options:
100 -verbose
104 This causes pnmtopng to display information about the format of
105 the output file.
106 -downscale
111 This enables pnmtopng to scale maxvalues of more then 65535 to
112 16 bits. Since this means loss of image data, pnmtopng does not
113 do it by default.
114 -interlace
119 This causes the PNG file to be interlaced, in Adam7 format. The
120 interlaced format is one in which the raster data starts with a
121 low-resolution representation of the entire image, then contin‐
122 ues with additional information for the entire image, then even
123 more information, etc. In Adam7 in particular, there are seven
124 such passes of the whole image. This is useful when you are re‐
125 ceiving the image over a slow communication line as someone is
126 waiting to see it. The simplest thing to do in that case is
127 wait for the entire image to arrive and then display it in‐
128 stantly, but then the user is wasting time staring at a blank
129 space until the whole image arrives. With the standard non-in‐
130 terlaced format, the data arrives row-by-row starting at the
131 top, so the displayer could display each row of the image as it
132 arrives and gradually paint down to the bottom. But with an in‐
133 terlaced image, the displayer can start by showing a low-resolu‐
134 tion version of the image, then gradually improve the display as
135 more data arrives.
136 -alpha=filename
141 This specifies the transparency (alpha) channel of the image.
142 You supply the transparency channel as a standard PGM transpar‐
143 ency mask (see the PGM(1) specification. pnmtopng does not nec‐
144 essarily represents the transparency information as a transpar‐
145 ency channel in the PNG format. If it can represent the trans‐
146 parency information through a palette, it will do so in order to
147 make a smaller PNG file. pnmtopng even sorts the palette so it
148 can omit the opaque colors from the transparency part of the
149 palette and save space for the palette.
150 -transparent=color
155 pnmtopng marks the specified color as transparent in the PNG im‐
156 age.
157 Specify the color (color) as described for the argument of the
159 pnm_parsecolor() library routine
160 ⟨libnetpbm_image.html#colorname⟩ . E.g. red or rgb:ff/00/0d.
161 If the color you specify is not present in the image, pnmtopng
162 selects instead the color in the image that is closest to the
163 one you specify. Closeness is measured as a Cartesian distance
164 between colors in RGB space. If multiple colors are equidis‐
165 tant, pnmtopng chooses one of them arbitrarily.
166 However, if you prefix your color specification with "=", e.g.
168 -transparent =red
170 only the exact color you specify will be transparent. If that
173 color does not appear in the image, there will be no transpar‐
174 ency. pnmtopng issues an information message when this is the
175 case.
176 -background=color
179 Causes pnmtopng to create a background color chunk in the PNG
180 output which can be used for subsequent transparency channel or
181 transparent color conversions. Specify color the same as for
182 -transparent.
183 -palette=palettefile
188 This option specifies a palette to use in the PNG. It forces
189 pnmtopng to create the paletted (colormapped) variety of PNG --
190 if that isn't possible, pnmtopng fails. If the palette you
191 specify doesn't contain exactly the colors in the image, pnm‐
192 topng fails. Since pnmtopng will automatically generate a
193 paletted PNG, with a correct palette, when appropriate, the only
194 reason you would specify the -palette option is if you care in
195 what order the colors appear in the palette. The PNG palette
196 has colors in the same order as the palette you specify.
197 You specify the palette by naming a PPM file that has one pixel
199 for each color in the palette.
200 Alternatively, consider the case that have a palette and you
202 want to make sure your PNG contains only colors from the pal‐
203 ette, approximating if necessary. You don't care what indexes
204 the PNG uses internally for the colors (i.e. the order of the
205 PNG palette). In this case, you don't need -palette. Pass the
206 Netpbm input image and your palette PPM through pnmremap.
207 Though you might think it would, using -palette in this case
208 wouldn't even save pnmtopng any work.
209 -gamma=value
212 Causes pnmtopng to create a gAMA chunk. This information helps
213 describe how the color values in the PNG must be interpreted.
214 Without the gAMA chunk, whatever interprets the PNG must get
215 this information separately (or just assume something standard).
216 If your input is a true PPM or PGM image, you should specify
217 -gamma=.52. But sometimes people generate images which are os‐
218 tensibly PPM except the image uses a different gamma transfer
219 function than the one specified for PPM. A common case of this
220 is when the image is created by simple hardware that doesn't
221 have digital computational ability. Also, some simple programs
222 that generate images from scratch do it with a gamma transfer in
223 which the gamma value is 1.0.
224 -hist Use this parameter to create a chunk that specifies the fre‐
229 quency (or histogram) of the colors in the image.
230 -text=filename
235 This option lets you include arbitrary text strings in the PNG
236 output, as tEXt chunks.
237 filename is the name of a file that contains your text strings.
239 The output contains a distinct tEXt chunk for each entry in the
241 file.
242 Here is an example of a text string file:
244 Title PNG file
246 Author John Doe
247 Description how to include a text chunk
248 PNG file
249 "Creation Date" 2015-may-11
250 Software pamtopng
251 The file is divided into entries, each entry comprising consecu‐
254 tive lines of text. The first line of an entry starts in the
255 first column (i.e. the first column is not white space) and ev‐
256 ery other line has white space in the first column. The first
257 entry starts in the first line, so it is not valid for the first
258 line of the file to have white space in its first column.
259 The first word in an entry is the key of the text string (e.g.
261 'Title'). It begins in column one of the line and continues up
262 to, but not including, the first delimiter character or the end
263 of the line, whichever is first. You can enclose the key in
264 double quotes in which case the key can consists of multiple
265 words. The quotes are not part of the key. The text string per
266 se begins after the key and any delimiter characters after it,
267 plus the text in subsequent continuation lines.
268 There is no limit on the length of a file line or entry or key
270 or text string. There is no limit on the number of entries.
271 -ztxt=filename
274 The same as -text, except the text string is compressed in the
275 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks,
276 unless the key for the text string starts with 'A' or 'T'. This
277 odd exception exists for backward compatibility; we don't know
278 why the program was originally designed this way, except that
279 the distinction was meant to roughly identify the keys 'Author'
280 and 'Title'.
281 -rgb=chroma_list
286 This option specifies how red, green, and blue component values
287 of a pixel specify a particular color, by telling the chromatic‐
288 ities of those 3 primary illuminants and of white (i.e. full
289 strength of all three).
290 The chroma_list value is a blank-separated list of 8 floating
292 point decimal numbers. The CIE-1931 X and Y chromaticities (in
293 that order) of each of white, red, green, and blue, in that or‐
294 der.
295 This information goes into the PNG's cHRM chunk.
297 In a shell command, make sure you use quotation marks so that
299 the blanks in chroma_list don't make the shell see multiple com‐
300 mand arguments.
301 This option was new in Netpbm 10.30 (October 2005). Before
303 that, the option -chroma does the same thing, but with slightly
304 different syntax.
305 -size="x y unit"
308 This option determines the aspect ratio of the individual pixels
309 of your image as well as the physical resolution of it.
310 unit is either 0 or 1. When it is 1, the option specifies the
312 physical resolution of the image in pixels per meter. For exam‐
313 ple, -size="10000 15000 1" means that when someone displays the
314 image, he should make it so that 10,000 pixels horizontally oc‐
315 cupy 1 meter and 15,000 pixels vertically occupy one meter. And
316 even if he doesn't take this advice on the overall size of the
317 displayed image, he should at least make it so that each pixel
318 displays as 1.5 times as high as wide.
319 When unit is 0, that means there is no advice on the absolute
321 physical resolution; just on the ratio of horizontal to vertical
322 physical resolution.
323 This information goes into the PNG's pHYS chunk.
325 When you don't specify -size, pnmtopng creates the image with no
327 pHYS chunk, which means square pixels of no absolute resolution.
328 This option was new in Netpbm 10.30 (October 2005). Before
330 that, the option -phys does the same thing, but with slightly
331 different syntax.
332 -srgbintent=intent
335 This asserts that the input is a pseudo-Netpbm image that uses
336 an sRGB color space (unlike true Netpbm) and indicates how you
337 intend for the colors to be rendered. It causes pnmtopng to in‐
338 clude an sRGB chunk in the PNG image that specifies that intent,
339 so see the PNG documentation for more information on what this
340 really means.
341 intent is one of:
343 • perceptual
347 • relativecolorimetric
349 • saturation
351 • absolutecolorimetric
353 This option was new in Netpbm 10.71 (June 2015). Before that,
356 pnmtopng never generates an sRGB chunk.
357 -modtime="[yy]yy-mm-dd hh:mm:ss"
360 This option allows you to specify the modification time value to
361 be placed in the PNG output. You can specify the year parameter
362 either as a two digit or four digit value.
363 This option was new in Netpbm 10.30 (October 2005). Before
365 that, the option -time does the same thing, but with slightly
366 different syntax.
367 -filter=n
370 This option is obsolete. Before Netpbm 10.22 (April 2004), this
371 was the only way to specify a row filter. It specifies a single
372 type of row filter, by number, that pnmtopng must use on each
373 row.
374 Use -nofilter, -sub, -up, -avg, and -paeth in current Netpbm.
376 -nofilter
379 -sub
381 -up
383 -avg
385 -paeth Each of these options permits pnmtopng to use one type of row
387 filter. pnmtopng chooses whichever of the permitted filters it
388 finds to be optimal. If you specify none of these options, it
389 is the same as specifying all of them -- pnmtopng uses any row
390 filter type it finds optimal.
391 These options were new with Netpbm 10.22 (April 2004). Before
393 that, you could use the -filter option to specify one permitted
394 row filter type. The default, when you specify no filter op‐
395 tions, was the same.
396 -compression=n
399 This option sets set the compression level of the zlib compres‐
400 sion. Select a level from 0 for no compression (maximum speed)
401 to 9 for maximum compression (minimum speed).
402 The default is the default of the zlib library.
404 -comp_mem_level=n
407 This option sets the memory usage level of the zlib compression.
408 Select a level from 1 for minimum memory usage (and minimum
409 speed) to 9 for maximum memory usage (and speed).
410 The default is the default of the zlib library.
412 This option was new in Netpbm 10.30 (October 2005).
414 -comp_strategy={huffman_only|filtered}
417 This options sets the compression strategy of the zlib compres‐
418 sion. See Zlib documentation for information on what these
419 strategies are.
420 The default is the default of the zlib library.
422 This option was new in Netpbm 10.30 (October 2005).
424 -comp_method=deflated
427 This option does nothing. It is here for mathematical complete‐
428 ness and for possible forward compatibility. It theoretically
429 selects the compression method of the zlib compression, but the
430 Z library knows only one method today, so there's nothing to
431 choose.
432 The default is the default of the zlib library.
434 This option was new in Netpbm 10.30 (October 2005).
436 -comp_window_bits=N
439 This option tells how big a window the zlib compression algo‐
440 rithm uses. The value is the base 2 logarithm of the window
441 size in bytes, so 8 means 256 bytes. The value must be from 8
442 to 15 (i.e. 256 bytes to 32K).
443 See Zlib documentation for details on what this window size is.
445 The default is the default of the zlib library.
447 This option was new in Netpbm 10.30 (October 2005).
449 -comp_buffer_size=N
452 This option determines in what size pieces pnmtopng does the
453 zlib compression. One compressed piece goes in each IDAT chunk
454 in the PNG. So the bigger this value, the fewer IDAT chunks
455 your PNG will have. Theoretically, this makes the PNG smaller
456 because 1) you have less per-IDAT-chunk overhead, and 2) the
457 compression algorithm has more data to work with. But in real‐
458 ity, the difference will probably not be noticeable above about
459 8K, which is the default.
460 The value n is the size of the compressed piece (i.e. the com‐
462 pression buffer) in bytes.
463 This option was new in Netpbm 10.30 (October 2005).
465 -force When you specify this, pnmtopng limits its optimizations. The
469 resulting PNG output is as similar to the Netpbm input as possi‐
470 ble. For example, the PNG output will not be paletted and the
471 transparency channel will be represented as a full transparency
472 channel even if the information could be represented more suc‐
473 cinctly with a transparency chunk.
474 -libversion
479 This option causes pnmtopng to display version information about
480 itself and the libraries it uses, in addition to all its normal
481 function. Do not confuse this with the Netpbm common option
482 -version, which causes the program to display version informa‐
483 tion about the Netpbm library and do nothing else.
484 You can't really use this option in a program that invokes pnm‐
486 topng and needs to know which version it is. Its function has
487 changed too much over the history of pnmtopng. The option is
488 good only for human eyes.
489
494 pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)
495 For information on the PNG format, see http://schaik.com/png
497 ⟨http://schaik.com/png⟩ .
498
501 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
502
504 This manual page was generated by the Netpbm tool 'makeman' from HTML
505 source. The master documentation is at
506 http://netpbm.sourceforge.net/doc/pnmtopng.html
508netpbm documentation 13 March 2019 Pnmtopng User Manual(0)