'\"
'\" Generated from file 'png\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2004, Code: Aaron Faupell <afaupell@users\&.sourceforge\&.net>
'\" Copyright (c) 2004, Doc: Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
'\"
.TH "png" n 0\&.1\&.2 tcllib "Image manipulation"
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See the \\*(So manual entry for details on the standard options.
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.BS
.SH NAME
png \- PNG querying and manipulation of meta data
.SH SYNOPSIS
package require \fBTcl  8\&.2\fR
.sp
package require \fBcrc32 \fR
.sp
package require \fBpng  ?0\&.1\&.2?\fR
.sp
\fB::png::validate\fR \fIfile\fR
.sp
\fB::png::isPNG\fR \fIfile\fR
.sp
\fB::png::imageInfo\fR \fIfile\fR
.sp
\fB::png::getTimestamp\fR \fIfile\fR
.sp
\fB::png::setTimestamp\fR \fIfile\fR \fItime\fR
.sp
\fB::png::getComments\fR \fIfile\fR
.sp
\fB::png::removeComments\fR \fIfile\fR
.sp
\fB::png::addComment\fR \fIfile\fR \fIkeyword\fR \fItext\fR
.sp
\fB::png::addComment\fR \fIfile\fR \fIkeyword\fR \fIlang\fR \fIkeyword2\fR \fItext\fR
.sp
\fB::png::image\fR \fIfile\fR
.sp
\fB::png::write\fR \fIfile\fR \fIdata\fR
.sp
.BE
.SH DESCRIPTION
.PP
This package provides commands to query and modify PNG images\&. PNG
stands for \fIPortable Network Graphics\fR and is specified at
\fIhttp://www\&.libpng\&.org/pub/png/spec/1\&.2\fR\&.
.SH COMMANDS
.TP
\fB::png::validate\fR \fIfile\fR
Returns a value indicating if \fIfile\fR is a valid PNG file\&. The file
is checked for PNG signature, each chunks checksum is verified,
existence of a data chunk is verified, first chunk is checked for
header, last chunk is checked for ending\&. Things \fInot\fR checked
for are: validity of values within a chunk, multiple header chunks,
noncontiguous data chunks, end chunk before actual eof\&. This procedure
can take lots of time\&.
.sp
Possible return values:
.RS
.TP
OK
File is a valid PNG file\&.
.TP
SIG
no/broken PNG signature\&.
.TP
BADLEN
corrupt chunk length\&.
.TP
EOF
premature end of file\&.
.TP
NOHDR
missing header chunk\&.
.TP
CKSUM
crc mismatch\&.
.TP
NODATA
missing data chunk(s)\&.
.TP
NOEND
missing end marker\&.
.RE
.TP
\fB::png::isPNG\fR \fIfile\fR
Returns a boolean value indicating if the file \fIfile\fR starts with
a PNG signature\&. This is a much faster and less intensive check than
\fB::png::validate\fR as it does not check if the PNG data is valid\&.
.TP
\fB::png::imageInfo\fR \fIfile\fR
Returns a dictionary with keys \fBwidth\fR, \fBheight\fR,
\fBdepth\fR, \fBcolor\fR, \fBcompression\fR, \fBfilter\fR, and
\fBinterlace\fR\&. The values are the associated properties of the PNG
image in \fIfile\fR\&.
Throws an error if file is not a PNG image, or if the checksum of the
header is invalid\&. For information on interpreting the values for the
returned properties see
\fIhttp://www\&.libpng\&.org/pub/png/spec/1\&.2/PNG-Chunks\&.html\fR\&.
.TP
\fB::png::getTimestamp\fR \fIfile\fR
Returns the epoch time if a timestamp chunk is found in the PNG image
contained in the \fIfile\fR, otherwise returns the empty string\&. Does
not attempt to verify the checksum of the timestamp chunk\&.
Throws an error if the \fIfile\fR is not a valid PNG image\&.
.TP
\fB::png::setTimestamp\fR \fIfile\fR \fItime\fR
Writes a new timestamp to the \fIfile\fR, either replacing the old
timestamp, or adding one just before the data chunks if there was no
previous timestamp\&. \fItime\fR is the new time in the gmt epoch
format\&.
Throws an error if \fIfile\fR is not a valid PNG image\&.
.TP
\fB::png::getComments\fR \fIfile\fR
Currently supports only uncompressed comments\&. Does not attempt to
verify the checksums of the comment chunks\&. Returns a list where each
element is a comment\&. Each comment is itself a list\&. The list for a
plain text comment consists of 2 elements: the human readable keyword,
and the text data\&. A unicode (international) comment consists of 4
elements: the human readable keyword, the language identifier, the
translated keyword, and the unicode text data\&.
Throws an error if \fIfile\fR is not a valid PNG image\&.
.TP
\fB::png::removeComments\fR \fIfile\fR
Removes all comments from the PNG image in \fIfile\fR\&. Beware - This
uses memory equal to the file size minus comments, to hold the
intermediate result\&.
Throws an error if \fIfile\fR is not a valid PNG image\&.
.TP
\fB::png::addComment\fR \fIfile\fR \fIkeyword\fR \fItext\fR
Adds a plain \fItext\fR comment to the PNG image in \fIfile\fR, just
before the first data chunk\&. Will throw an error if no data chunk is
found\&. \fIkeyword\fR has to be less than 80 characters long to conform
to the PNG specification\&.
.TP
\fB::png::addComment\fR \fIfile\fR \fIkeyword\fR \fIlang\fR \fIkeyword2\fR \fItext\fR
Adds a unicode (international) comment to the PNG image in \fIfile\fR,
just before the first data chunk\&. Will throw an error if no data chunk
is found\&. \fIkeyword\fR has to be less than 80 characters long to
conform to the PNG specification\&. \fIkeyword2\fR is the translated
\fIkeyword\fR, in the language specified by the language identifier
\fIlang\fR\&.
.TP
\fB::png::image\fR \fIfile\fR
Given a PNG file returns the image in the list of scanlines format used by Tk_GetColor\&.
.TP
\fB::png::write\fR \fIfile\fR \fIdata\fR
Takes a list of scanlines in the Tk_GetColor format and writes the represented image
to \fIfile\fR\&.
.PP
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fIpng\fR of the
\fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.SH KEYWORDS
comment, image, png, timestamp
.SH CATEGORY
File formats
.SH COPYRIGHT
.nf
Copyright (c) 2004, Code: Aaron Faupell <afaupell@users\&.sourceforge\&.net>
Copyright (c) 2004, Doc:  Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>

.fi