1png(n) Image manipulation png(n)
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6
8 png - PNG querying and manipulation of meta data
9
11 package require Tcl 8.2
12 package require crc32
14 package require png ?0.1.1?
16 ::png::validate file
18 ::png::isPNG file
20 ::png::imageInfo file
22 ::png::getTimestamp file
24 ::png::setTimestamp file time
26 ::png::getComments file
28 ::png::removeComments file
30 ::png::addComment file keyword text
32 ::png::addComment file keyword lang keyword2 text
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36
38 This package provides commands to query and modify PNG images. PNG
39 stands for Portable Network Graphics and is specified at
40 http://www.libpng.org/pub/png/spec/1.2.
41
43 ::png::validate file
44 Returns a value indicating if file is a valid PNG file. The file
45 is checked for PNG signature, each chunks checksum is verified,
46 existence of a data chunk is verified, first chunk is checked
47 for header, last chunk is checked for ending. Things not checked
48 for are: validity of values within a chunk, multiple header
49 chunks, noncontiguous data chunks, end chunk before actual eof.
50 This procedure can take lots of time.
51 Possible return values:
53 OK File is a valid PNG file.
55 SIG no/broken PNG signature.
57 BADLEN corrupt chunk length.
59 EOF premature end of file.
61 NOHDR missing header chunk.
63 CKSUM crc mismatch.
65 NODATA missing data chunk(s).
67 NOEND missing end marker.
69 ::png::isPNG file
71 Returns a boolean value indicating if the file file starts with
72 a PNG signature. This is a much faster and less intensive check
73 than ::png::validate as it does not check if the PNG data is
74 valid.
75 ::png::imageInfo file
77 Returns a dictionary with keys width, height, depth, color, com‐
78 pression, filter, and interlace. The values are the associated
79 properties of the PNG image in file. Throws an error if file is
80 not a PNG image, or if the checksum of the header is invalid.
81 For information on interpreting the values for the returned
82 properties see http://www.libpng.org/pub/png/spec/1.2/PNG-
83 Chunks.html.
84 ::png::getTimestamp file
86 Returns the epoch time if a timestamp chunk is found in the PNG
87 image contained in the file, otherwise returns the empty string.
88 Does not attempt to verify the checksum of the timestamp chunk.
89 Throws an error if the file is not a valid PNG image.
90 ::png::setTimestamp file time
92 Writes a new timestamp to the file, either replacing the old
93 timestamp, or adding one just before the data chunks if there
94 was no previous timestamp. time is the new time in the gmt epoch
95 format. Throws an error if file is not a valid PNG image.
96 ::png::getComments file
98 Currently supports only uncompressed comments. Does not attempt
99 to verify the checksums of the comment chunks. Returns a list
100 where each element is a comment. Each comment is itself a list.
101 The list for a plain text comment consists of 2 elements: the
102 human readable keyword, and the text data. A unicode (interna‐
103 tional) comment consists of 4 elements: the human readable key‐
104 word, the language identifier, the translated keyword, and the
105 unicode text data. Throws an error if file is not a valid PNG
106 image.
107 ::png::removeComments file
109 Removes all comments from the PNG image in file. Beware - This
110 uses memory equal to the file size minus comments, to hold the
111 intermediate result. Throws an error if file is not a valid PNG
112 image.
113 ::png::addComment file keyword text
115 Adds a plain text comment to the PNG image in file, just before
116 the first data chunk. Will throw an error if no data chunk is
117 found. keyword has to be less than 80 characters long to conform
118 to the PNG specification.
119 ::png::addComment file keyword lang keyword2 text
121 Adds a unicode (international) comment to the PNG image in file,
122 just before the first data chunk. Will throw an error if no data
123 chunk is found. keyword has to be less than 80 characters long
124 to conform to the PNG specification. keyword2 is the translated
125 keyword, in the language specified by the language identifier
126 lang.
127
129 comment, image, png, timestamp
130
132 Copyright (c) 2004, Code: Aaron Faupell <afaupell@users.sourceforge.net>
133 Copyright (c) 2004, Doc: Andreas Kupries <andreas_kupries@users.sourceforge.net>
134png 0.1.1 png(n)