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
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 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
71 hyphens 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
79 argument 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
107 This enables pnmtopng to scale maxvalues of more then 65535 to
108 16 bits. Since this means loss of image data, pnmtopng does not
109 do it by default.
110 -interlace
113 This causes the PNG file to be interlaced, in Adam7 format. The
114 interlaced format is one in which the raster data starts with a
115 low-resolution representation of the entire image, then contin‐
116 ues with additional information for the entire image, then even
117 more information, etc. In Adam7 in particular, there are seven
118 such passes of the whole image. This is useful when you are
119 receiving the image over a slow communication line as someone is
120 waiting to see it. The simplest thing to do in that case is
121 wait for the entire image to arrive and then display it
122 instantly, but then the user is wasting time staring at a blank
123 space until the whole image arrives. With the standard non-
124 interlaced format, the data arrives row-by-row starting at the
125 top, so the displayer could display each row of the image as it
126 arrives and gradually paint down to the bottom. But with an
127 interlaced image, the displayer can start by showing a low-reso‐
128 lution version of the image, then gradually improve the display
129 as more data arrives.
130 -alpha=filename
134 This specifies the transparency (alpha) channel of the image.
135 You supply the transparency channel as a standard PGM trans‐
136 parency mask (see the PGM(1) specification. pnmtopng does not
137 necessarily represents the transparency information as a trans‐
138 parency channel in the PNG format. If it can represent the
139 transparency information through a palette, it will do so in
140 order to make a smaller PNG file. pnmtopng even sorts the pal‐
141 ette so it can omit the opaque colors from the transparency part
142 of the palette and save space for the palette.
143 -transparent=color
146 pnmtopng marks the specified color as transparent in the PNG
147 image.
148 Specify the color (color) as described for the argument of the
150 pnm_parsecolor() library routine
151 ⟨libnetpbm_image.html#colorname⟩ . E.g. red or rgb:ff/00/0d.
152 If the color you specify is not present in the image, pnmtopng
153 selects instead the color in the image that is closest to the
154 one you specify. Closeness is measured as a Cartesian distance
155 between colors in RGB space. If multiple colors are equidis‐
156 tant, pnmtopng chooses one of them arbitrarily.
157 However, if you prefix your color specification with "=", e.g.
159 -transparent =red
161 only the exact color you specify will be transparent. If that
163 color does not appear in the image, there will be no trans‐
164 parency. pnmtopng issues an information message when this is
165 the case.
166 -background=color
169 Causes pnmtopng to create a background color chunk in the PNG
170 output which can be used for subsequent transparency channel or
171 transparent color conversions. Specify color the same as for
172 -transparent.
173 -palette=palettefile
176 This option specifies a palette to use in the PNG. It forces
177 pnmtopng to create the paletted (colormapped) variety of PNG --
178 if that isn't possible, pnmtopng fails. If the palette you
179 specify doesn't contain exactly the colors in the image, pnm‐
180 topng fails. Since pnmtopng will automatically generate a
181 paletted PNG, with a correct palette, when appropriate, the only
182 reason you would specify the -palette option is if you care in
183 what order the colors appear in the palette. The PNG palette
184 has colors in the same order as the palette you specify.
185 You specify the palette by naming a PPM file that has one pixel
187 for each color in the palette.
188 Alternatively, consider the case that have a palette and you
190 want to make sure your PNG contains only colors from the pal‐
191 ette, approximating if necessary. You don't care what indexes
192 the PNG uses internally for the colors (i.e. the order of the
193 PNG palette). In this case, you don't need -palette. Pass the
194 Netpbm input image and your palette PPM through pnmremap.
195 Though you might think it would, using -palette in this case
196 wouldn't even save pnmtopng any work.
197 -gamma=value
200 Causes pnmtopng to create a gAMA chunk. This information helps
201 describe how the color values in the PNG must be interpreted.
202 Without the gAMA chunk, whatever interprets the PNG must get
203 this information separately (or just assume something standard).
204 If your input is a true PPM or PGM image, you should specify
205 -gamma=.52. But sometimes people generate images which are
206 ostensibly PPM except the image uses a different gamma transfer
207 function than the one specified for PPM. A common case of this
208 is when the image is created by simple hardware that doesn't
209 have digital computational ability. Also, some simple programs
210 that generate images from scratch do it with a gamma transfer in
211 which the gamma value is 1.0.
212 -hist Use this parameter to create a chunk that specifies the fre‐
215 quency (or histogram) of the colors in the image.
216 -text=filename
219 This option lets you include arbitrary text strings in the PNG
220 output, as tEXt chunks.
221 filename is the name of a file that contains your text strings.
223 The output contains a distinct tEXt chunk for each entry in the
225 file.
226 Here is an example of a text string file:
228 Title PNG file
230 Author John Doe
231 Description how to include a text chunk
232 PNG file
233 "Creation Date" 2015-may-11
234 Software pamtopng
235 The file is divided into entries, each entry comprising consecu‐
237 tive lines of text. The first line of an entry starts in the
238 first column (i.e. the first column is not white space) and
239 every other line has white space in the first column. The first
240 entry starts in the first line, so it is not valid for the first
241 line of the file to have white space in its first column.
242 The first word in an entry is the key of the text string (e.g.
244 'Title'). It begins in column one of the line and continues up
245 to, but not including, the first delimiter character or the end
246 of the line, whichever is first. You can enclose the key in
247 double quotes in which case the key can consists of multiple
248 words. The quotes are not part of the key. The text string per
249 se begins after the key and any delimiter characters after it,
250 plus the text in subsequent continuation lines.
251 There is no limit on the length of a file line or entry or key
253 or text string. There is no limit on the number of entries.
254 -ztxt=filename
257 The same as -text, except the text string is compressed in the
258 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks,
259 unless the key for the text string starts with 'A' or 'T'. This
260 odd exception exists for backward compatibility; we don't know
261 why the program was originally designed this way, except that
262 the distinction was meant to roughly identify the keys 'Author'
263 and 'Title'.
264 -rgb=chroma_list
267 This option specifies how red, green, and blue component values
268 of a pixel specify a particular color, by telling the chromatic‐
269 ities of those 3 primary illuminants and of white (i.e. full
270 strength of all three).
271 The chroma_list value is a blank-separated list of 8 floating
273 point decimal numbers. The CIE-1931 X and Y chromaticities (in
274 that order) of each of white, red, green, and blue, in that
275 order.
276 This information goes into the PNG's cHRM chunk.
278 In a shell command, make sure you use quotation marks so that
280 the blanks in chroma_list don't make the shell see multiple com‐
281 mand arguments.
282 This option was new in Netpbm 10.30 (October 2005). Before
284 that, the option -chroma does the same thing, but with slightly
285 different syntax.
286 -size="x y unit"
289 This option determines the aspect ratio of the individual pixels
290 of your image as well as the physical resolution of it.
291 unit is either 0 or 1. When it is 1, the option specifies the
293 physical resolution of the image in pixels per meter. For exam‐
294 ple, -size="10000 15000 1" means that when someone displays the
295 image, he should make it so that 10,000 pixels horizontally
296 occupy 1 meter and 15,000 pixels vertically occupy one meter.
297 And even if he doesn't take this advice on the overall size of
298 the displayed image, he should at least make it so that each
299 pixel displays as 1.5 times as high as wide.
300 When unit is 0, that means there is no advice on the absolute
302 physical resolution; just on the ratio of horizontal to vertical
303 physical resolution.
304 This information goes into the PNG's pHYS chunk.
306 When you don't specify -size, pnmtopng creates the image with no
308 pHYS chunk, which means square pixels of no absolute resolution.
309 This option was new in Netpbm 10.30 (October 2005). Before
311 that, the option -phys does the same thing, but with slightly
312 different syntax.
313 -srgbintent=intent
316 This asserts that the input is a pseudo-Netpbm image that uses
317 an sRGB color space (unlike true Netpbm) and indicates how you
318 intend for the colors to be rendered. It causes pnmtopng to
319 include an sRGB chunk in the PNG image that specifies that
320 intent, so see the PNG documentation for more information on
321 what this really means.
322 intent is one of:
324 · perceptual
328 · relativecolorimetric
330 · saturation
332 · absolutecolorimetric
334 This option was new in Netpbm 10.71 (June 2015). Before that,
337 pnmtopng never generates an sRGB chunk.
338 -modtime="[yy]yy-mm-dd hh:mm:ss"
341 This option allows you to specify the modification time value to
342 be placed in the PNG output. You can specify the year parameter
343 either as a two digit or four digit value.
344 This option was new in Netpbm 10.30 (October 2005). Before
346 that, the option -time does the same thing, but with slightly
347 different syntax.
348 -filter=n
351 This option is obsolete. Before Netpbm 10.22 (April 2004), this
352 was the only way to specify a row filter. It specifies a single
353 type of row filter, by number, that pnmtopng must use on each
354 row.
355 Use -nofilter, -sub, -up, -avg, and -paeth in current Netpbm.
357 -nofilter
360 -sub
362 -up
364 -avg
366 -paeth Each of these options permits pnmtopng to use one type of row
368 filter. pnmtopng chooses whichever of the permitted filters it
369 finds to be optimal. If you specify none of these options, it
370 is the same as specifying all of them -- pnmtopng uses any row
371 filter type it finds optimal.
372 These options were new with Netpbm 10.22 (April 2004). Before
374 that, you could use the -filter option to specify one permitted
375 row filter type. The default, when you specify no filter
376 options, was the same.
377 -compression=n
380 This option sets set the compression level of the zlib compres‐
381 sion. Select a level from 0 for no compression (maximum speed)
382 to 9 for maximum compression (minimum speed).
383 The default is the default of the zlib library.
385 -comp_mem_level=n
388 This option sets the memory usage level of the zlib compression.
389 Select a level from 1 for minimum memory usage (and minimum
390 speed) to 9 for maximum memory usage (and speed).
391 The default is the default of the zlib library.
393 This option was new in Netpbm 10.30 (October 2005).
395 -comp_strategy={huffman_only|filtered}
398 This options sets the compression strategy of the zlib compres‐
399 sion. See Zlib documentation for information on what these
400 strategies are.
401 The default is the default of the zlib library.
403 This option was new in Netpbm 10.30 (October 2005).
405 -comp_method=deflated
408 This option does nothing. It is here for mathematical complete‐
409 ness and for possible forward compatibility. It theoretically
410 selects the compression method of the zlib compression, but the
411 Z library knows only one method today, so there's nothing to
412 choose.
413 The default is the default of the zlib library.
415 This option was new in Netpbm 10.30 (October 2005).
417 -comp_window_bits=N
420 This option tells how big a window the zlib compression algo‐
421 rithm uses. The value is the base 2 logarithm of the window
422 size in bytes, so 8 means 256 bytes. The value must be from 8
423 to 15 (i.e. 256 bytes to 32K).
424 See Zlib documentation for details on what this window size is.
426 The default is the default of the zlib library.
428 This option was new in Netpbm 10.30 (October 2005).
430 -comp_buffer_size=N
433 This option determines in what size pieces pnmtopng does the
434 zlib compression. One compressed piece goes in each IDAT chunk
435 in the PNG. So the bigger this value, the fewer IDAT chunks
436 your PNG will have. Theoretically, this makes the PNG smaller
437 because 1) you have less per-IDAT-chunk overhead, and 2) the
438 compression algorithm has more data to work with. But in real‐
439 ity, the difference will probably not be noticeable above about
440 8K, which is the default.
441 The value n is the size of the compressed piece (i.e. the com‐
443 pression buffer) in bytes.
444 This option was new in Netpbm 10.30 (October 2005).
446 -force When you specify this, pnmtopng limits its optimizations. The
450 resulting PNG output is as similar to the Netpbm input as possi‐
451 ble. For example, the PNG output will not be paletted and the
452 transparency channel will be represented as a full transparency
453 channel even if the information could be represented more suc‐
454 cinctly with a transparency chunk.
455 -libversion
458 This option causes pnmtopng to display version information about
459 itself and the libraries it uses, in addition to all its normal
460 function. Do not confuse this with the Netpbm common option
461 -version, which causes the program to display version informa‐
462 tion about the Netpbm library and do nothing else.
463 You can't really use this option in a program that invokes pnm‐
465 topng and needs to know which version it is. Its function has
466 changed too much over the history of pnmtopng. The option is
467 good only for human eyes.
468
473 pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)
474 For information on the PNG format, see http://schaik.com/png
476 ⟨http://schaik.com/png⟩ .
477
480 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
481
483 This manual page was generated by the Netpbm tool 'makeman' from HTML
484 source. The master documentation is at
485 http://netpbm.sourceforge.net/doc/pnmtopng.html
487netpbm documentation 13 March 2019 Pnmtopng User Manual(0)