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png(n)                                       Image manipulation                                       png(n)



____________________________________________________________________________________________________________

NAME
       png - PNG querying and manipulation of meta data

SYNOPSIS
       package require Tcl  8.2

       package require crc32

       package require png  ?0.1.2?

       ::png::validate file

       ::png::isPNG file

       ::png::imageInfo file

       ::png::getTimestamp file

       ::png::setTimestamp file time

       ::png::getComments file

       ::png::removeComments file

       ::png::addComment file keyword text

       ::png::addComment file keyword lang keyword2 text

____________________________________________________________________________________________________________

DESCRIPTION
       This package provides commands to query and modify PNG images. PNG stands for Portable Network Graph-ics Graphics
       ics and is specified at http://www.libpng.org/pub/png/spec/1.2.

COMMANDS
       ::png::validate file
              Returns a value indicating if file 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 not 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.

              Possible return values:

              OK     File is a valid PNG file.

              SIG    no/broken PNG signature.

              BADLEN corrupt chunk length.

              EOF    premature end of file.

              NOHDR  missing header chunk.

              CKSUM  crc mismatch.

              NODATA missing data chunk(s).

              NOEND  missing end marker.

       ::png::isPNG file
              Returns a boolean value indicating if the file file starts with a PNG  signature.  This  is  a
              much faster and less intensive check than ::png::validate as it does not check if the PNG data
              is valid.

       ::png::imageInfo file
              Returns a dictionary with keys width, height, depth, color, compression,  filter,  and  inter-lace. interlace.
              lace.  The  values are the associated properties of the PNG image in file.  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
              http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html.

       ::png::getTimestamp file
              Returns the epoch time if a timestamp chunk is found in the PNG image contained in  the  file,
              otherwise  returns  the empty string. Does not attempt to verify the checksum of the timestamp
              chunk.  Throws an error if the file is not a valid PNG image.

       ::png::setTimestamp file time
              Writes a new timestamp to the file, either replacing the old timestamp,  or  adding  one  just
              before  the  data  chunks  if there was no previous timestamp. time is the new time in the gmt
              epoch format.  Throws an error if file is not a valid PNG image.

       ::png::getComments file
              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 key-word, keyword,
              word, the language identifier, the translated keyword, and the unicode text data.   Throws  an
              error if file is not a valid PNG image.

       ::png::removeComments file
              Removes  all  comments from the PNG image in file. Beware - This uses memory equal to the file
              size minus comments, to hold the intermediate result.  Throws an error if file is not a  valid
              PNG image.

       ::png::addComment file keyword text
              Adds  a  plain  text  comment to the PNG image in file, just before the first data chunk. Will
              throw an error if no data chunk is found. keyword has to be less than 80  characters  long  to
              conform to the PNG specification.

       ::png::addComment file keyword lang keyword2 text
              Adds  a  unicode  (international) comment to the PNG image in file, just before the first data
              chunk. Will throw an error if no data chunk is found. keyword has to be less than  80  charac-ters characters
              ters long to conform to the PNG specification. keyword2 is the translated keyword, in the lan-guage language
              guage specified by the language identifier lang.


BUGS, IDEAS, FEEDBACK
       This document, and the package it describes,  will  undoubtedly  contain  bugs  and  other  problems.
       Please   report   such   in   the   category   png   of   the   Tcllib  SF  Trackers  [http://source -
       forge.net/tracker/? group_id=12883].  Please also report any ideas for enhancements you may  have  for
       either package and/or documentation.

KEYWORDS
       comment, image, png, timestamp

CATEGORY
       File formats

COPYRIGHT
       Copyright (c) 2004, Code: Aaron Faupell <afaupell@users.sourceforge.net>
       Copyright (c) 2004, Doc:  Andreas Kupries <andreas_kupries@users.sourceforge.net>




png                                                 0.1.2                                             png(n)