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 ?0.1.2?
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
34 ::png::image file
36 ::png::write file data
38______________________________________________________________________________
40
42 This package provides commands to query and modify PNG images. PNG
43 stands for Portable Network Graphics and is specified at
44 http://www.libpng.org/pub/png/spec/1.2.
45
47 ::png::validate file
48 Returns a value indicating if file is a valid PNG file. The file
49 is checked for PNG signature, each chunks checksum is verified,
50 existence of a data chunk is verified, first chunk is checked
51 for header, last chunk is checked for ending. Things not checked
52 for are: validity of values within a chunk, multiple header
53 chunks, noncontiguous data chunks, end chunk before actual eof.
54 This procedure can take lots of time.
55 Possible return values:
57 OK File is a valid PNG file.
59 SIG no/broken PNG signature.
61 BADLEN corrupt chunk length.
63 EOF premature end of file.
65 NOHDR missing header chunk.
67 CKSUM crc mismatch.
69 NODATA missing data chunk(s).
71 NOEND missing end marker.
73 ::png::isPNG file
75 Returns a boolean value indicating if the file file starts with
76 a PNG signature. This is a much faster and less intensive check
77 than ::png::validate as it does not check if the PNG data is
78 valid.
79 ::png::imageInfo file
81 Returns a dictionary with keys width, height, depth, color, com‐
82 pression, filter, and interlace. The values are the associated
83 properties of the PNG image in file. Throws an error if file is
84 not a PNG image, or if the checksum of the header is invalid.
85 For information on interpreting the values for the returned
86 properties see http://www.libpng.org/pub/png/spec/1.2/PNG-
87 Chunks.html.
88 ::png::getTimestamp file
90 Returns the epoch time if a timestamp chunk is found in the PNG
91 image contained in the file, otherwise returns the empty string.
92 Does not attempt to verify the checksum of the timestamp chunk.
93 Throws an error if the file is not a valid PNG image.
94 ::png::setTimestamp file time
96 Writes a new timestamp to the file, either replacing the old
97 timestamp, or adding one just before the data chunks if there
98 was no previous timestamp. time is the new time in the gmt epoch
99 format. Throws an error if file is not a valid PNG image.
100 ::png::getComments file
102 Currently supports only uncompressed comments. Does not attempt
103 to verify the checksums of the comment chunks. Returns a list
104 where each element is a comment. Each comment is itself a list.
105 The list for a plain text comment consists of 2 elements: the
106 human readable keyword, and the text data. A unicode (interna‐
107 tional) comment consists of 4 elements: the human readable key‐
108 word, the language identifier, the translated keyword, and the
109 unicode text data. Throws an error if file is not a valid PNG
110 image.
111 ::png::removeComments file
113 Removes all comments from the PNG image in file. Beware - This
114 uses memory equal to the file size minus comments, to hold the
115 intermediate result. Throws an error if file is not a valid PNG
116 image.
117 ::png::addComment file keyword text
119 Adds a plain text comment to the PNG image in file, just before
120 the first data chunk. Will throw an error if no data chunk is
121 found. keyword has to be less than 80 characters long to conform
122 to the PNG specification.
123 ::png::addComment file keyword lang keyword2 text
125 Adds a unicode (international) comment to the PNG image in file,
126 just before the first data chunk. Will throw an error if no data
127 chunk is found. keyword has to be less than 80 characters long
128 to conform to the PNG specification. keyword2 is the translated
129 keyword, in the language specified by the language identifier
130 lang.
131 ::png::image file
133 Given a PNG file returns the image in the list of scanlines for‐
134 mat used by Tk_GetColor.
135 ::png::write file data
137 Takes a list of scanlines in the Tk_GetColor format and writes
138 the represented image to file.
139
141 This document, and the package it describes, will undoubtedly contain
142 bugs and other problems. Please report such in the category png of the
143 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
144 report any ideas for enhancements you may have for either package
145 and/or documentation.
146 When proposing code changes, please provide unified diffs, i.e the out‐
148 put of diff -u.
149 Note further that attachments are strongly preferred over inlined
151 patches. Attachments can be made by going to the Edit form of the
152 ticket immediately after its creation, and then using the left-most
153 button in the secondary navigation bar.
154
156 comment, image, png, timestamp
157
159 File formats
160
162 Copyright (c) 2004, Code: Aaron Faupell <afaupell@users.sourceforge.net>
163 Copyright (c) 2004, Doc: Andreas Kupries <andreas_kupries@users.sourceforge.net>
164tcllib 0.1.2 png(n)