1Pngtopnm User Manual(0) Pngtopnm User Manual(0)
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6 pngtopnm - convert a PNG image into a PNM image
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10 pngtopnm [-verbose] [-alpha | -mix] [-background=color] [-gamma=value]
11 [-text=filename] [-time] [pngfile]
12 Minimum unique abbreviation of option is acceptable. You may use dou‐
14 ble hyphens instead of single hyphen to denote options. You may use
15 white space in place of the equals sign to separate an option name from
16 its value.
17
20 This program is part of Netpbm(1).
21 pngtopnm reads a PNG image (Portable Network Graphics) as input and
23 produces a PPM image as output. The type of the output file depends on
24 the input file - if it's black & white, pngtopnm creates a PBM file.
25 If it's grayscale, pngtopnm creates a PGM file. Otherwise, it creates
26 a PPM file.
27
30 -verbose
31 Display various information about the input PNG image and the
32 conversion process.
33 If you want even more information about the PNG image, use
35 pngcheck (not part of Netpbm).
36 -alpha Output the alpha channel or transparency mask of the image. The
39 result is either a PBM file or a PGM file, depending on whether
40 different levels of transparency appear.
41 -mix Compose the image with the transparency or alpha mask against a
44 background. The background color is determined by the bKGD
45 chunk in the PNG, except that you can override it with -back‐
46 ground. If the PNG has no bKGD chunk and you don't specify
47 -background, the background color is white.
48 -background=color
51 This option specifies the background color with which to mix the
52 image when you specify -mix.
53 color is as described for the argument of the ppm_parsecolor()
55 library routine ⟨libppm.html#colorname⟩ .
56 Examples:
58 · -background=rgb:01/ff/80
62 · -background=rgbi:1/255/128
64 If you don't specify -background, the background color is what
67 is specified in the PNG image, and if the PNG doesn't specify
68 anything, white.
69 You cannot specify -background unless you also specify -mix.
71 Before Netpbm 10.27 (March 2005), you could specify -background
72 with -mix and it was just ignored. (This caused a usability
73 problem).
74 -gamma= value
78 Converts the image to a new display-gamma value. If a gAMA
79 chunk is present in the png-file, pngtopnm uses the specified
80 image-gamma value. If not, pngtopnm considers the image-gamma
81 to be 1.0. Based on the image-gamma and the display-gamma given
82 with this option, pngtopnm adjusts the colors written to the
83 pnm-file.
84 Because the gammas of uncompensated monitors are around 2.6,
86 which results in an image-gamma of 0.45, some typical situations
87 are: when the image-gamma is 0.45 (use -verbose to check) and
88 the picture is too light, your system is gamma-corrected, so
89 convert with '-gamma 1.0'. When no gAMA chunk is present or the
90 image-gamma is 1.0, use 2.2 to make the picture lighter and 0.45
91 to make the picture darker.
92 -text=file
95 Writes the tEXt and zTXt chunks to a file, in a format as
96 described in the pnmtopng user manual. These chunks contain
97 text comments or annotations.
98 -time Prints the tIME chunk to stderr.
101
106 pnmtopng(1), ptot, pnmgamma(1), pnm(1)
107 For information on the PNG format, see http://schaik.com/png
109 ⟨http://schaik.com/png⟩ .
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113 A PNG image contains a lot of information that can't be represented in
114 Netpbm formats. Therefore, you lose information when you convert to
115 another format with "pngtopnm | pnmtoxxx". If there is a specialized
116 converter that converts directly to the other format, e.g. ptot to con‐
117 vert from PNG to TIFF, you'll get better results using that.
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121 There could be an option to read the comment text from pnm comments
122 instead of a separate file.
123 The program could be much faster, with a bit of code optimizing. As
125 with any Netpbm program, speed always takes a back seat to quick
126 present and future development.
127
130 Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
131netpbm documentation 24 March 2005 Pngtopnm User Manual(0)