1Pamtopng User Manual(0) Pamtopng User Manual(0)
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6 pamtopng - convert a Netpbm image to PNG
7
10 pamtopng [-verbose] [-transparent=color] [-background=color]
11 [-gamma=value] [-chroma='wx wy
12 rx ry gx gy bx by'] [-srgbintent=intent] [-time=[yy]yy-mm-dd
13 hh:mm:ss] [-text=file] [-ztxt=file] [-itxt=file] [-interlace] [pnm‐
14 file]
15
18 Minimum unique abbreviation of option is acceptable. You may use dou‐
19 ble hyphens instead of a single hyphen to denote options. You may use
20 white space in place of the equals sign to separate an option name from
21 its value.
22
25 This program is part of Netpbm(1).
26 pamtopng reads a Netpbm image as input and produces a PNG image as out‐
28 put.
29 Color component values in PNG files are either 8 or 16 bits wide, so
31 where necessary pamtopng scales colors to have a maxval of 255 or
32 65535. In that case, it will add an sBIT chunk to indicated the origi‐
33 nal bit-depth.
34 pamtopng works only on images with maxval 1, 3, 15, 255, or 65535. You
36 can use pamdepth to convert an image with some other maxval to one of
37 these.
38 pamtopng produces a color PNG from a color PAM, even if the only colors
40 in the image are shades of gray. To create a graycale PNG, from such
41 an image (which might be slightly smaller), you can use other Netpbm
42 programs to convert the input to grayscale.
43 Alternative: pnmtopng
46 Netpbm contains another program for generating PNG images: pnmtopng.
47 pnmtopng is a much older program - it is in fact the first program in
48 the world that could generate a PNG. pnmtopng is a complex, feature-
49 laden program. It lets you control various arcane aspects of the con‐
50 version and create PNGs with various arcane features. It does various
51 transformations on the image to create the greatest compression possi‐
52 ble, to a degree that probably doesn't make any difference in the mod‐
53 ern world.
54 The main advantage pamtopng has over pnmtopng is that the former can
56 use the transparency channel of a PAM image to generate the trans‐
57 parency information in the PNG. In contrast, handling of the alpha
58 channel is very cumbersome with pnmotpng.
59 One difference that does not exist, that some people might incorrectly
61 infer from the names is the possible input formats. Both programs can
62 take PBM, PGM, PPM, and PAM input.
63 Because pnmtopng has been around virtually forever, programs and proce‐
65 dures that use it are more portable than those that use pamtopng. Its
66 age and popularity also probably make it have fewer bugs.
67 pamtopng does not have any way to do what the following do in pnmtopng:
69 · -palette
73 · -history
75 · -filter
77 · -size
79 · -paeth
81 · -hist
83 · -nofilter
85 · -sub
87 · -up
89 · -avg
91 · -force
93 · -libversion
95 · -compression
97 · -comp_xxx
99 These are some of the other functions of pnmtopng that pamtopng lacks:
102 · When you specify a transparent or background color that is not
106 in the image, pnmtopng can optionally choose the closest one
107 that is in the image. pamtopng always uses the exact color you
108 specify.
109 Features that exist in both programs are controlled by largely the same
112 command syntax. But there are these differences:
113 · pnmtopng's -rgb option is -chroma in pamtopng. -chroma is a
117 better name, and in fact was the name that pnmtopng used origi‐
118 nally, but we had to change it when we had to change the syntax
119 of the option value to conform to the rest of Netpbm.
120 · pnmtopng's -modtime option is -time in pamtopng. The origin of
123 -modtime is analogous to that of -rgb.
124
130 -transparent=color
131 pamtopng marks the specified color as transparent in the PNG
132 image.
133 Specify the color (color) as described for the argument of the
135 pnm_parsecolor() library routine
136 ⟨libnetpbm_image.html#colorname⟩ . E.g. red or rgb:ff/00/0d.
137 -background=color
140 This causes pamtopng to create a background color chunk in the
141 PNG output which can be used for subsequent transparency channel
142 or transparent color conversions. Specify color the same as for
143 -transparent.
144 -gamma=value
147 This causes pnmtopng to create a gAMA chunk. This information
148 helps describe how the color values in the PNG must be inter‐
149 preted. Without the gAMA chunk, whatever interprets the PNG
150 must get this information separately (or just assume something
151 standard). If your input is a true PPM or PGM image, you should
152 specify -gamma=.45. But sometimes people generate images which
153 are ostensibly PPM except the image uses a different gamma
154 transfer function than the one specified for PPM. A common case
155 of this is when the image is created by simple hardware that
156 doesn't have digital computational ability. Also, some simple
157 programs that generate images from scratch do it with a gamma
158 transfer in which the gamma value is 1.0.
159 -chroma=chroma_list
162 This option specifies how red, green, and blue component values
163 of a pixel specify a particular color, by telling the chromatic‐
164 ities of those 3 primary illuminants and of white (i.e. full
165 strength of all three).
166 The chroma_list value is a blank-separated list of 8 floating
168 point decimal numbers. The CIE-1931 X and Y chromaticities (in
169 that order) of each of white, red, green, and blue, in that
170 order.
171 This information goes into the PNG's cHRM chunk.
173 In a shell command, make sure you use quotation marks so that
175 the blanks in chroma_list don't make the shell see multiple com‐
176 mand arguments.
177 -srgbintent=intent
180 This asserts that the input is a pseudo-Netpbm image that uses
181 an sRGB color space (unlike true Netpbm) and indicates how you
182 intend for the colors to be rendered. It causes pamtopng to
183 include an sRGB chunk in the PNG image that specifies that
184 intent, so see the PNG documentation for more information on
185 what this really means.
186 intent is one of:
188 · perceptual
192 · relativecolorimetric
194 · saturation
196 · absolutecolorimetric
198 -text=filename
202 This option lets you include arbitrary text strings in the PNG
203 output, as tEXt chunks.
204 filename is the name of a file that contains your text strings.
206 The output contains a distinct tEXt chunk for each entry in the
208 file.
209 Here is an example of a text string file:
211 Title PNG file
213 Author John Doe
214 Description how to include a text chunk
215 PNG file
216 "Creation Date" 2015-may-11
217 Software pamtopng
218 The file is divided into entries, each entry comprising consecu‐
220 tive lines of text. The first line of an entry starts in the
221 first column (i.e. the first column is not white space) and
222 every other line has white space in the first column. The first
223 entry starts in the first line, so it is not valid for the first
224 line of the file to have white space in its first column.
225 The first word in an entry is the key of the text string (e.g.
227 'Title'). It begins in column one of the line and continues up
228 to, but not including, the first delimiter character or the end
229 of the line, whichever is first. You can enclose the key in
230 double quotes in which case the key can consists of multiple
231 words. The quotes are not part of the key. The text string per
232 se begins after the key and any delimiter characters after it,
233 plus the text in subsequent continuation lines.
234 There is no limit on the length of a file line or entry or key
236 or text string. There is no limit on the number of entries.
237 -ztxt=filename
240 The same as -text, except the text string is compressed in the
241 PNG output. pnmtopng uses zTXt chunks instead of a tEXt chunks.
242 -itxt=filename
245 Similar to -text, but the text strings can be in a language
246 other than English. The PNG image indicates what language that
247 is and includes the text string key both in English and that
248 language. pnmtopng uses iTXt chunks instead of tEXt chunks.
249 For each record, you must specify the language and give the key
251 both in English and in the text string language.
252 Example:
254 Language nl-NL Taal nl-NL
256 Title nl-NL Titel PNG file
257 Author nl-NL Auteur Pietje Puk
258 Description nl-NL Omschrijving Tekst in het Nederlands.
259 The language specification is based on the ISO 639-1 standard,
261 see http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes for the
262 valid codes. The format is either a two character "nl" or an
263 extended code like "en-US".
264 -time='[yy]yy-mm-dd hh:mm:ss'
267 This option allows you to specify the modification time value to
268 be placed in the PNG output. You can specify the year parameter
269 either as a two or four digit value.
270 -interlace
273 This causes the PNG file to be interlaced, in Adam7 format. The
274 interlaced format is one in which the raster data starts with a
275 low-resolution representation of the entire image, then contin‐
276 ues with additional information for the entire image, then even
277 more information, etc. In Adam7 in particular, there are seven
278 such passes of the whole image. This is useful when you are
279 receiving the image over a slow communication line as someone is
280 waiting to see it. The simplest thing to do in that case is
281 wait for the entire image to arrive and then display it
282 instantly, but then the user is wasting time staring at a blank
283 space until the whole image arrives. With the standard non-
284 interlaced format, the data arrives row-by-row starting at the
285 top, so the displayer could display each row of the image as it
286 arrives and gradually paint down to the bottom. But with an
287 interlaced image, the displayer can start by showing a low-reso‐
288 lution version of the image, then gradually improve the display
289 as more data arrives.
290 When you specify this option, pamtopng must hold the entire
292 image in memory at once, whereas without it, the program holds
293 only one raster row at a time. If you don't have enough memory
294 for that, you might suffer extreme slowdowns or failure - not
295 just in the process running pamtopng, but potentially throughout
296 the system that shares memory with it. pnmtopng does not have
297 this limitation (it holds only one row at a time in memory even
298 when generating an interlaced PNG).
299 This option was new in Netpbm 10.86 (March 2019).
301 -verbose
304 This causes the program to display various facts about the con‐
305 version.
306
312 pngtopam(1), pnmtopng(1), pam(1), pnm(1)
313 For information on the PNG format, see http://www.w3.org/TR/PNG/
315 ⟨http://www.w3.org/TR/PNG/⟩ , http://libpng.org/pub/png/
316 ⟨http://libpng.org/pub/png/⟩ ,
317 http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
318 ⟨http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes⟩ and
319 http://schaik.com/png/ ⟨http://schaik.com/png/⟩ .
320
323 pamtopng was new in Netpbm 10.70 (June 2015).
324 Before pamtopng, the two ways to create PNG images with Netpbm were
326 pnmtopng and pamrgbatopng. The history of the former is discussed
327 above. The latter was added to Netpbm in 2005 as a cheap way to fill a
328 significant need that pnmtopng did not: the ability to turn the alpha
329 channel in a PAM image into the alpha channel in a PNG image.
330 Handling of the alpha channel with pnmtopng is very cumbersome (as was
332 dealing with alpha channels in general before the introduction of the
333 PAM format). pamrgbatopng could do what people wanted with the alpha
334 channel, but nothing else. It was a very small program with literally
335 no command line options.
336 The goal in those days was eventually to expand pnmtopng to do the PAM
338 alpha channel thing, rename it to pamtopng, and retire pamrgbatopng.
339 But pnmtopng is such a complex program, because of its dizzying array
340 of features and its need for backward compatibility, that adding that
341 one capability to it was a daunting task and for ten years nobody
342 attempted it.
343 In 2015, one of the authors of the original pnmtopng (from before it
345 was even part of Netpbm -- a program that shared essentially no lines
346 of code with pnmtopng of 2015) decided to go in a different direction.
347 While many features of pnmtopng were pretty important and easy to
348 implement, many others were probably of no use in the modern world or
349 at least not important enough to justify the complexity they lent to
350 the code. (The features thought to be outdated were ones that were
351 intended to make the PNG output slightly smaller - something consider‐
352 ably less important with the declining cost of computer resources).
353 And there was an opportunity to drop those features: We could use the
355 new name 'pamtopng' for a new program, keep the existing program under
356 the name 'pnmtopng', and avoid most backward compatibility trouble.
357 Therefore, Willem van Schaik wrote an intermediate level program that
359 had all the most important features of pnmtopng, plus the alpha channel
360 handling of pamrgbatopng, with nice, simple code. That was pamtopng.
361 Because pamrgbatopng had no options, pamtopng was backward compatible
363 with it without even trying. Therefore, as soon as we added pamtopng
364 to Netpbm, we removed pamrgbatopng and recommended that pamrgbatopng be
365 installed as an alias for pamtopng.
366
370 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
371 Copyright (C) 2015 by Willem van Schaik.
372
374 This manual page was generated by the Netpbm tool 'makeman' from HTML
375 source. The master documentation is at
376 http://netpbm.sourceforge.net/doc/pamtopng.html
378netpbm documentation 13 March 2019 Pamtopng User Manual(0)