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
85 pnmtopng -size "800 800 0" input.pnm > output.png
87 If you're writing a program that needs to work with both new and old ,
89 have it first try with the new syntax, and if it fails with "unrecog‐
90 nized option," fall back to the old syntax.
91 Current Options
94 In addition to the options common to all programs based on libnetpbm
95 (most notably -quiet, see
96 Common Options ⟨index.html#commonoptions⟩ ), pnmtopng recognizes the
97 following command line options:
98 -verbose
102 This causes pnmtopng to display information about the format of
103 the output file.
104 -downscale
109 This enables pnmtopng to scale maxvalues of more then 65535 to
110 16 bits. Since this means loss of image data, pnmtopng does not
111 do it by default.
112 -interlace
117 This causes the PNG file to be interlaced, in Adam7 format. The
118 interlaced format is one in which the raster data starts with a
119 low-resolution representation of the entire image, then contin‐
120 ues with additional information for the entire image, then even
121 more information, etc. In Adam7 in particular, there are seven
122 such passes of the whole image. This is useful when you are re‐
123 ceiving the image over a slow communication line as someone is
124 waiting to see it. The simplest thing to do in that case is
125 wait for the entire image to arrive and then display it in‐
126 stantly, but then the user is wasting time staring at a blank
127 space until the whole image arrives. With the standard non-in‐
128 terlaced format, the data arrives row-by-row starting at the
129 top, so the displayer could display each row of the image as it
130 arrives and gradually paint down to the bottom. But with an in‐
131 terlaced image, the displayer can start by showing a low-resolu‐
132 tion version of the image, then gradually improve the display as
133 more data arrives.
134 -alpha=filename
139 This specifies the transparency (alpha) channel of the image.
140 You supply the transparency channel as a standard PGM transpar‐
141 ency mask (see the PGM(1) specification. pnmtopng does not nec‐
142 essarily represents the transparency information as a transpar‐
143 ency channel in the PNG format. If it can represent the trans‐
144 parency information through a palette, it will do so in order to
145 make a smaller PNG file. pnmtopng even sorts the palette so it
146 can omit the opaque colors from the transparency part of the
147 palette and save space for the palette.
148 -transparent=color
153 pnmtopng marks the specified color as transparent in the PNG im‐
154 age.
155 Specify the color (color) as described for the argument of the
157 pnm_parsecolor() library routine
158 ⟨libnetpbm_image.html#colorname⟩ . E.g. red or rgb:ff/00/0d.
159 If the color you specify is not present in the image, pnmtopng
160 selects instead the color in the image that is closest to the
161 one you specify. Closeness is measured as a Cartesian distance
162 between colors in RGB space. If multiple colors are equidis‐
163 tant, pnmtopng chooses one of them arbitrarily.
164 However, if you prefix your color specification with "=", e.g.
166 -transparent =red
168 only the exact color you specify will be transparent. If that
170 color does not appear in the image, there will be no transpar‐
171 ency. pnmtopng issues an information message when this is the
172 case.
173 -background=color
176 Causes pnmtopng to create a background color chunk in the PNG
177 output which can be used for subsequent transparency channel or
178 transparent color conversions. Specify color the same as for
179 -transparent.
180 -palette=palettefile
185 This option specifies a palette to use in the PNG. It forces
186 pnmtopng to create the paletted (colormapped) variety of PNG --
187 if that isn't possible, pnmtopng fails. If the palette you
188 specify doesn't contain exactly the colors in the image, pnm‐
189 topng fails. Since pnmtopng will automatically generate a
190 paletted PNG, with a correct palette, when appropriate, the only
191 reason you would specify the -palette option is if you care in
192 what order the colors appear in the palette. The PNG palette
193 has colors in the same order as the palette you specify.
194 You specify the palette by naming a PPM file that has one pixel
196 for each color in the palette.
197 Alternatively, consider the case that have a palette and you
199 want to make sure your PNG contains only colors from the pal‐
200 ette, approximating if necessary. You don't care what indexes
201 the PNG uses internally for the colors (i.e. the order of the
202 PNG palette). In this case, you don't need -palette. Pass the
203 Netpbm input image and your palette PPM through pnmremap.
204 Though you might think it would, using -palette in this case
205 wouldn't even save pnmtopng any work.
206 -gamma=value
209 Causes pnmtopng to create a gAMA chunk. This information helps
210 describe how the color values in the PNG must be interpreted.
211 Without the gAMA chunk, whatever interprets the PNG must get
212 this information separately (or just assume something standard).
213 If your input is a true PPM or PGM image, you should specify
214 -gamma=.52. But sometimes people generate images which are os‐
215 tensibly PPM except the image uses a different gamma transfer
216 function than the one specified for PPM. A common case of this
217 is when the image is created by simple hardware that doesn't
218 have digital computational ability. Also, some simple programs
219 that generate images from scratch do it with a gamma transfer in
220 which the gamma value is 1.0.
221 -hist Use this parameter to create a chunk that specifies the fre‐
226 quency (or histogram) of the colors in the image.
227 -text=filename
232 This option lets you include arbitrary text strings in the PNG
233 output, as tEXt chunks.
234 filename is the name of a file that contains your text strings.
236 The output contains a distinct tEXt chunk for each entry in the
238 file.
239 Here is an example of a text string file:
241 Title PNG file
243 Author John Doe
244 Description how to include a text chunk
245 PNG file
246 "Creation Date" 2015-may-11
247 Software pamtopng
248 The file is divided into entries, each entry comprising consecu‐
250 tive lines of text. The first line of an entry starts in the
251 first column (i.e. the first column is not white space) and ev‐
252 ery other line has white space in the first column. The first
253 entry starts in the first line, so it is not valid for the first
254 line of the file to have white space in its first column.
255 The first word in an entry is the key of the text string (e.g.
257 'Title'). It begins in column one of the line and continues up
258 to, but not including, the first delimiter character or the end
259 of the line, whichever is first. You can enclose the key in
260 double quotes in which case the key can consists of multiple
261 words. The quotes are not part of the key. The text string per
262 se begins after the key and any delimiter characters after it,
263 plus the text in subsequent continuation lines.
264 There is no limit on the length of a file line or entry or key
266 or text string. There is no limit on the number of entries.
267 -ztxt=filename
270 The same as -text, except the text string is compressed in the
271 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks,
272 unless the key for the text string starts with 'A' or 'T'. This
273 odd exception exists for backward compatibility; we don't know
274 why the program was originally designed this way, except that
275 the distinction was meant to roughly identify the keys 'Author'
276 and 'Title'.
277 -rgb=chroma_list
282 This option specifies how red, green, and blue component values
283 of a pixel specify a particular color, by telling the chromatic‐
284 ities of those 3 primary illuminants and of white (i.e. full
285 strength of all three).
286 The chroma_list value is a blank-separated list of 8 floating
288 point decimal numbers. The CIE-1931 X and Y chromaticities (in
289 that order) of each of white, red, green, and blue, in that or‐
290 der.
291 This information goes into the PNG's cHRM chunk.
293 In a shell command, make sure you use quotation marks so that
295 the blanks in chroma_list don't make the shell see multiple com‐
296 mand arguments.
297 This option was new in Netpbm 10.30 (October 2005). Before
299 that, the option -chroma does the same thing, but with slightly
300 different syntax.
301 -size="x y unit"
304 This option determines the aspect ratio of the individual pixels
305 of your image as well as the physical resolution of it.
306 unit is either 0 or 1. When it is 1, the option specifies the
308 physical resolution of the image in pixels per meter. For exam‐
309 ple, -size="10000 15000 1" means that when someone displays the
310 image, he should make it so that 10,000 pixels horizontally oc‐
311 cupy 1 meter and 15,000 pixels vertically occupy one meter. And
312 even if he doesn't take this advice on the overall size of the
313 displayed image, he should at least make it so that each pixel
314 displays as 1.5 times as high as wide.
315 When unit is 0, that means there is no advice on the absolute
317 physical resolution; just on the ratio of horizontal to vertical
318 physical resolution.
319 This information goes into the PNG's pHYS chunk.
321 When you don't specify -size, pnmtopng creates the image with no
323 pHYS chunk, which means square pixels of no absolute resolution.
324 This option was new in Netpbm 10.30 (October 2005). Before
326 that, the option -phys does the same thing, but with slightly
327 different syntax.
328 -srgbintent=intent
331 This asserts that the input is a pseudo-Netpbm image that uses
332 an sRGB color space (unlike true Netpbm) and indicates how you
333 intend for the colors to be rendered. It causes pnmtopng to in‐
334 clude an sRGB chunk in the PNG image that specifies that intent,
335 so see the PNG documentation for more information on what this
336 really means.
337 intent is one of:
339 • perceptual
343 • relativecolorimetric
345 • saturation
347 • absolutecolorimetric
349 This option was new in Netpbm 10.71 (June 2015). Before that,
352 pnmtopng never generates an sRGB chunk.
353 -modtime="[yy]yy-mm-dd hh:mm:ss"
356 This option allows you to specify the modification time value to
357 be placed in the PNG output. You can specify the year parameter
358 either as a two digit or four digit value.
359 This option was new in Netpbm 10.30 (October 2005). Before
361 that, the option -time does the same thing, but with slightly
362 different syntax.
363 -filter=n
366 This option is obsolete. Before Netpbm 10.22 (April 2004), this
367 was the only way to specify a row filter. It specifies a single
368 type of row filter, by number, that pnmtopng must use on each
369 row.
370 Use -nofilter, -sub, -up, -avg, and -paeth in current Netpbm.
372 -nofilter
375 -sub
377 -up
379 -avg
381 -paeth Each of these options permits pnmtopng to use one type of row
383 filter. pnmtopng chooses whichever of the permitted filters it
384 finds to be optimal. If you specify none of these options, it
385 is the same as specifying all of them -- pnmtopng uses any row
386 filter type it finds optimal.
387 These options were new with Netpbm 10.22 (April 2004). Before
389 that, you could use the -filter option to specify one permitted
390 row filter type. The default, when you specify no filter op‐
391 tions, was the same.
392 -compression=n
395 This option sets set the compression level of the zlib compres‐
396 sion. Select a level from 0 for no compression (maximum speed)
397 to 9 for maximum compression (minimum speed).
398 The default is the default of the zlib library.
400 -comp_mem_level=n
403 This option sets the memory usage level of the zlib compression.
404 Select a level from 1 for minimum memory usage (and minimum
405 speed) to 9 for maximum memory usage (and speed).
406 The default is the default of the zlib library.
408 This option was new in Netpbm 10.30 (October 2005).
410 -comp_strategy={huffman_only|filtered}
413 This options sets the compression strategy of the zlib compres‐
414 sion. See Zlib documentation for information on what these
415 strategies are.
416 The default is the default of the zlib library.
418 This option was new in Netpbm 10.30 (October 2005).
420 -comp_method=deflated
423 This option does nothing. It is here for mathematical complete‐
424 ness and for possible forward compatibility. It theoretically
425 selects the compression method of the zlib compression, but the
426 Z library knows only one method today, so there's nothing to
427 choose.
428 The default is the default of the zlib library.
430 This option was new in Netpbm 10.30 (October 2005).
432 -comp_window_bits=N
435 This option tells how big a window the zlib compression algo‐
436 rithm uses. The value is the base 2 logarithm of the window
437 size in bytes, so 8 means 256 bytes. The value must be from 8
438 to 15 (i.e. 256 bytes to 32K).
439 See Zlib documentation for details on what this window size is.
441 The default is the default of the zlib library.
443 This option was new in Netpbm 10.30 (October 2005).
445 -comp_buffer_size=N
448 This option determines in what size pieces pnmtopng does the
449 zlib compression. One compressed piece goes in each IDAT chunk
450 in the PNG. So the bigger this value, the fewer IDAT chunks
451 your PNG will have. Theoretically, this makes the PNG smaller
452 because 1) you have less per-IDAT-chunk overhead, and 2) the
453 compression algorithm has more data to work with. But in real‐
454 ity, the difference will probably not be noticeable above about
455 8K, which is the default.
456 The value n is the size of the compressed piece (i.e. the com‐
458 pression buffer) in bytes.
459 This option was new in Netpbm 10.30 (October 2005).
461 -force When you specify this, pnmtopng limits its optimizations. The
465 resulting PNG output is as similar to the Netpbm input as possi‐
466 ble. For example, the PNG output will not be paletted and the
467 transparency channel will be represented as a full transparency
468 channel even if the information could be represented more suc‐
469 cinctly with a transparency chunk.
470 -libversion
475 This option causes pnmtopng to display version information about
476 itself and the libraries it uses, in addition to all its normal
477 function. Do not confuse this with the Netpbm common option
478 -version, which causes the program to display version informa‐
479 tion about the Netpbm library and do nothing else.
480 You can't really use this option in a program that invokes pnm‐
482 topng and needs to know which version it is. Its function has
483 changed too much over the history of pnmtopng. The option is
484 good only for human eyes.
485
490 pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)
491 For information on the PNG format, see http://schaik.com/png
493 ⟨http://schaik.com/png⟩ .
494
497 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
498
500 This manual page was generated by the Netpbm tool 'makeman' from HTML
501 source. The master documentation is at
502 http://netpbm.sourceforge.net/doc/pnmtopng.html
504netpbm documentation 13 March 2019 Pnmtopng User Manual(0)