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 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 This causes pnmtopng to display information about the format of
95 the output file.
96 -downscale
99 This enables pnmtopng to scale maxvalues of more then 65535 to
100 16 bits. Since this means loss of image data, pnmtopng does not
101 do it by default.
102 -interlace
105 This causes the PNG file to be interlaced, in Adam7 format. The
106 interlaced format is one in which the raster data starts with a
107 low-resolution representation of the entire image, then contin‐
108 ues with additional information for the entire image, then even
109 more information, etc. In Adam7 in particular, there are seven
110 such passes of the whole image. This is useful when you are
111 receiving the image over a slow communication line as someone is
112 waiting to see it. The simplest thing to do in that case is
113 wait for the entire image to arrive and then display it
114 instantly, but then the user is wasting time staring at a blank
115 space until the whole image arrives. With the standard non-
116 interlaced format, the data arrives row-by-row starting at the
117 top, so the displayer could display each row of the image as it
118 arrives and gradually paint down to the bottom. But with an
119 interlaced image, the displayer can start by showing a low-reso‐
120 lution version of the image, then gradually improve the display
121 as more data arrives.
122 -alpha=filename
125 This specifies the transparency (alpha) channel of the image.
126 You supply the transparency channel as a standard PGM trans‐
127 parency mask (see the PGM(1) specification. pnmtopng does not
128 necessarily represents the transparency information as a trans‐
129 parency channel in the PNG format. If it can represent the
130 transparency information through a palette, it will do so in
131 order to make a smaller PNG file. pnmtopng even sorts the pal‐
132 ette so it can omit the opaque colors from the transparency part
133 of the palette and save space for the palette.
134 -transparent=color
137 pnmtopng marks the specified color as transparent in the PNG
138 image.
139 Specify the color (color) as described for the argument of the
141 pnm_parsecolor() library routine
142 ⟨libnetpbm_image.html#colorname⟩ . E.g. red or rgb:ff/00/0d.
143 If the color you specify is not present in the image, pnmtopng
144 selects instead the color in the image that is closest to the
145 one you specify. Closeness is measured as a Cartesian distance
146 between colors in RGB space. If multiple colors are equidis‐
147 tant, pnmtopng chooses one of them arbitrarily.
148 However, if you prefix your color specification with "=", e.g.
150 -transparent =red
152 only the exact color you specify will be transparent. If that
154 color does not appear in the image, there will be no trans‐
155 parency. pnmtopng issues an information message when this is
156 the case.
157 -background=color
160 Causes pnmtopng to create a background color chunk in the PNG
161 output which can be used for subsequent transparency channel or
162 transparent color conversions. Specify color the same as for
163 -transparent.
164 -palette=palettefile
167 This option specifies a palette to use in the PNG. It forces
168 pnmtopng to create the paletted (colormapped) variety of PNG --
169 if that isn't possible, pnmtopng fails. If the palette you
170 specify doesn't contain exactly the colors in the image, pnm‐
171 topng fails. Since pnmtopng will automatically generate a
172 paletted PNG, with a correct palette, when appropriate, the only
173 reason you would specify the -palette option is if you care in
174 what order the colors appear in the palette. The PNG palette
175 has colors in the same order as the palette you specify.
176 You specify the palette by naming a PPM file that has one pixel
178 for each color in the palette.
179 Alternatively, consider the case that have a palette and you
181 want to make sure your PNG contains only colors from the pal‐
182 ette, approximating if necessary. You don't care what indexes
183 the PNG uses internally for the colors (i.e. the order of the
184 PNG palette). In this case, you don't need -palette. Pass the
185 Netpbm input image and your palette PPM through pnmremap.
186 Though you might think it would, using -palette in this case
187 wouldn't even save pnmtopng any work.
188 -gamma=value
191 Causes pnmtopng to create a gAMA chunk. This information helps
192 describe how the color values in the PNG must be interpreted.
193 Without the gAMA chunk, whatever interprets the PNG must get
194 this information separately (or just assume something standard).
195 If your input is a true PPM or PGM image, you should specify
196 -gamma=.52. But sometimes people generate images which are
197 ostensibly PPM except the image uses a different gamma transfer
198 function than the one specified for PPM. A common case of this
199 is when the image is created by simple hardware that doesn't
200 have digital computational ability. Also, some simple programs
201 that generate images from scratch do it with a gamma transfer in
202 which the gamma value is 1.0.
203 -hist Use this parameter to create a chunk that specifies the fre‐
206 quency (or histogram) of the colors in the image.
207 -text=filename
210 This option lets you include arbitrary text strings in the PNG
211 output, as tEXt chunks.
212 filename is the name of a file that contains your text strings.
214 The output contains a distinct tEXt chunk for each entry in the
216 file.
217 Here is an example of a text string file:
219 Title PNG file
221 Author John Doe
222 Description how to include a text chunk
223 PNG file
224 "Creation Date" 2015-may-11
225 Software pamtopng
226 The file is divided into entries, each entry comprising consecu‐
228 tive lines of text. The first line of an entry starts in the
229 first column (i.e. the first column is not white space) and
230 every other line has white space in the first column. The first
231 entry starts in the first line, so it is not valid for the first
232 line of the file to have white space in its first column.
233 The first word in an entry is the key of the text string (e.g.
235 'Title'). It begins in column one of the line and continues up
236 to, but not including, the first delimiter character or the end
237 of the line, whichever is first. You can enclose the key in
238 double quotes in which case the key can consists of multiple
239 words. The quotes are not part of the key. The text string per
240 se begins after the key and any delimiter characters after it,
241 plus the text in subsequent continuation lines.
242 There is no limit on the length of a file line or entry or key
244 or text string. There is no limit on the number of entries.
245 -ztxt=filename
248 The same as -text, except the text string is compressed in the
249 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks,
250 unless the key for the text string starts with 'A' or 'T'. This
251 odd exception exists for backward compatibility; we don't know
252 why the program was originally designed this way, except that
253 the distinction was meant to roughly identify the keys 'Author'
254 and 'Title'.
255 -rgb=chroma_list
259 This option specifies how red, green, and blue component values
260 of a pixel specify a particular color, by telling the chromatic‐
261 ities of those 3 primary illuminants and of white (i.e. full
262 strength of all three).
263 The chroma_list value is a blank-separated list of 8 floating
265 point decimal numbers. The CIE-1931 X and Y chromaticities (in
266 that order) of each of white, red, green, and blue, in that
267 order.
268 This information goes into the PNG's cHRM chunk.
270 In a shell command, make sure you use quotation marks so that
272 the blanks in chroma_list don't make the shell see multiple com‐
273 mand arguments.
274 This option was new in Netpbm 10.30 (October 2005). Before
276 that, the option -chroma does the same thing, but with slightly
277 different syntax.
278 -size="x y unit"
281 This option determines the aspect ratio of the individual pixels
282 of your image as well as the physical resolution of it.
283 unit is either 0 or 1. When it is 1, the option specifies the
285 physical resolution of the image in pixels per meter. For exam‐
286 ple, -size="10000 15000 1" means that when someone displays the
287 image, he should make it so that 10,000 pixels horizontally
288 occupy 1 meter and 15,000 pixels vertically occupy one meter.
289 And even if he doesn't take this advice on the overall size of
290 the displayed image, he should at least make it so that each
291 pixel displays as 1.5 times as high as wide.
292 When unit is 0, that means there is no advice on the absolute
294 physical resolution; just on the ratio of horizontal to vertical
295 physical resolution.
296 This information goes into the PNG's pHYS chunk.
298 When you don't specify -size, pnmtopng creates the image with no
300 pHYS chunk, which means square pixels of no absolute resolution.
301 This option was new in Netpbm 10.30 (October 2005). Before
303 that, the option -phys does the same thing, but with slightly
304 different syntax.
305 -srgbintent=intent
308 This asserts that the input is a pseudo-Netpbm image that uses
309 an sRGB color space (unlike true Netpbm) and indicates how you
310 intend for the colors to be rendered. It causes pnmtopng to
311 include an sRGB chunk in the PNG image that specifies that
312 intent, so see the PNG documentation for more information on
313 what this really means.
314 intent is one of:
316 · perceptual
320 · relativecolorimetric
322 · saturation
324 · absolutecolorimetric
326 This option was new in Netpbm 10.71 (June 2015). Before that,
329 pnmtopng never generates an sRGB chunk.
330 -modtime="[yy]yy-mm-dd hh:mm:ss"
333 This option allows you to specify the modification time value to
334 be placed in the PNG output. You can specify the year parameter
335 either as a two digit or four digit value.
336 This option was new in Netpbm 10.30 (October 2005). Before
338 that, the option -time does the same thing, but with slightly
339 different syntax.
340 -filter=n
343 This option is obsolete. Before Netpbm 10.22 (April 2004), this
344 was the only way to specify a row filter. It specifies a single
345 type of row filter, by number, that pnmtopng must use on each
346 row.
347 Use -nofilter, -sub, -up, -avg, and -paeth in current Netpbm.
349 -nofilter
352 -sub
354 -up
356 -avg
358 -paeth Each of these options permits pnmtopng to use one type of row
360 filter. pnmtopng chooses whichever of the permitted filters it
361 finds to be optimal. If you specify none of these options, it
362 is the same as specifying all of them -- pnmtopng uses any row
363 filter type it finds optimal.
364 These options were new with Netpbm 10.22 (April 2004). Before
366 that, you could use the -filter option to specify one permitted
367 row filter type. The default, when you specify no filter
368 options, was the same.
369 -compression=n
372 This option sets set the compression level of the zlib compres‐
373 sion. Select a level from 0 for no compression (maximum speed)
374 to 9 for maximum compression (minimum speed).
375 The default is the default of the zlib library.
377 -comp_mem_level=n
380 This option sets the memory usage level of the zlib compression.
381 Select a level from 1 for minimum memory usage (and minimum
382 speed) to 9 for maximum memory usage (and speed).
383 The default is the default of the zlib library.
385 This option was new in Netpbm 10.30 (October 2005).
387 -comp_strategy={huffman_only|filtered}
390 This options sets the compression strategy of the zlib compres‐
391 sion. See Zlib documentation for information on what these
392 strategies are.
393 The default is the default of the zlib library.
395 This option was new in Netpbm 10.30 (October 2005).
397 -comp_method=deflated
400 This option does nothing. It is here for mathematical complete‐
401 ness and for possible forward compatibility. It theoretically
402 selects the compression method of the zlib compression, but the
403 Z library knows only one method today, so there's nothing to
404 choose.
405 The default is the default of the zlib library.
407 This option was new in Netpbm 10.30 (October 2005).
409 -comp_window_bits=N
412 This option tells how big a window the zlib compression algo‐
413 rithm uses. The value is the base 2 logarithm of the window
414 size in bytes, so 8 means 256 bytes. The value must be from 8
415 to 15 (i.e. 256 bytes to 32K).
416 See Zlib documentation for details on what this window size is.
418 The default is the default of the zlib library.
420 This option was new in Netpbm 10.30 (October 2005).
422 -comp_buffer_size=N
425 This option determines in what size pieces pnmtopng does the
426 zlib compression. One compressed piece goes in each IDAT chunk
427 in the PNG. So the bigger this value, the fewer IDAT chunks
428 your PNG will have. Theoretically, this makes the PNG smaller
429 because 1) you have less per-IDAT-chunk overhead, and 2) the
430 compression algorithm has more data to work with. But in real‐
431 ity, the difference will probably not be noticeable above about
432 8K, which is the default.
433 The value n is the size of the compressed piece (i.e. the com‐
435 pression buffer) in bytes.
436 This option was new in Netpbm 10.30 (October 2005).
438 -force When you specify this, pnmtopng limits its optimizations. The
442 resulting PNG output is as similar to the Netpbm input as possi‐
443 ble. For example, the PNG output will not be paletted and the
444 transparency channel will be represented as a full transparency
445 channel even if the information could be represented more suc‐
446 cinctly with a transparency chunk.
447 -libversion
451 This option causes pnmtopng to display version information about
452 itself and the libraries it uses, in addition to all its normal
453 function. Do not confuse this with the Netpbm common option
454 -version, which causes the program to display version informa‐
455 tion about the Netpbm library and do nothing else.
456 You can't really use this option in a program that invokes pnm‐
458 topng and needs to know which version it is. Its function has
459 changed too much over the history of pnmtopng. The option is
460 good only for human eyes.
461
466 pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)
467 For information on the PNG format, see http://schaik.com/png
469 ⟨http://schaik.com/png⟩ .
470
473 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
474
476 This manual page was generated by the Netpbm tool 'makeman' from HTML
477 source. The master documentation is at
478 http://netpbm.sourceforge.net/doc/pnmtopng.html
480netpbm documentation 13 March 2019 Pnmtopng User Manual(0)