Provided by: tcllib_1.15-dfsg-2_all 
NAME
jpeg - JPEG querying and manipulation of meta data
SYNOPSIS
package require Tcl 8.2
package require jpeg ?0.4.0?
::jpeg::isJPEG file
::jpeg::imageInfo file
::jpeg::dimensions file
::jpeg::getThumbnail file
::jpeg::getExif file ?section?
::jpeg::getExifFromChannel channel ?section?
::jpeg::formatExif keys
::jpeg::exifKeys
::jpeg::removeExif file
::jpeg::stripJPEG file
::jpeg::getComments file
::jpeg::addComment file text...
::jpeg::removeComments file
::jpeg::replaceComment file text
::jpeg::debug file
::jpeg::markers channel
_________________________________________________________________
DESCRIPTION
This package provides commands to query and modify JPEG images. JPEG stands for Joint Photography Experts
Group and is a standard for the lossy compression of photographical images. It is specified at LINK_HERE.
COMMANDS
::jpeg::isJPEG file
Returns a boolean value indicating if file is a JPEG image.
::jpeg::imageInfo file
Returns a dictionary with keys version, units, xdensity, ydensity, xthumb, and ythumb. The values
are the associated properties of the JPEG image in file. Throws an error if file is not a JPEG
image.
::jpeg::dimensions file
Returns the dimensions of the JPEG file as a list of the horizontal and vertical pixel count.
Throws an error if file is not a JPEG image.
::jpeg::getThumbnail file
This procedure will return the binary thumbnail image data, if a JPEG thumbnail is included in
file, and the empty string otherwise. Note that it is possible to include thumbnails in formats
other than JPEG although that is not common. The command finds thumbnails that are encoded in
either the JFXX or EXIF segments of the JPEG information. If both are present the EXIF thumbnail
will take precedence. Throws an error if file is not a JPEG image.
set fh [open thumbnail.jpg w+]
fconfigure $fh -translation binary -encoding binary
puts -nonewline $fh [::jpeg::getThumbnail photo.jpg]
close $fh
::jpeg::getExif file ?section?
section must be one of main or thumbnail. The default is main. Returns a dictionary containing
the EXIF information for the specified section. For example:
set exif {
Make Canon
Model {Canon DIGITAL IXUS}
DateTime {2001:06:09 15:17:32}
}
Throws an error if file is not a JPEG image.
::jpeg::getExifFromChannel channel ?section?
This command is as per ::jpeg::getExif except that it uses a previously opened channel. channel
should be a seekable channel and section is as described in the documentation of ::jpeg::getExif
Note: the jpeg parser expects that the start of the channel is the start of the image data. If
working with an image embedded in a container file format it may be necessary to read the jpeg
data into a temporary container: either a temporary file or a memory channel.
::jpeg::formatExif keys
Takes a list of key-value pairs as returned by getExif and formats many of the values into a more
human readable form. As few as one key-value may be passed in, the entire exif is not required.
foreach {key val} [::jpeg::formatExif [::jpeg::getExif photo.jpg]] {
puts "$key: $val"
}
array set exif [::jpeg::getExif photo.jpg]
puts "max f-stop: [::jpeg::formatExif [list MaxAperture $exif(MaxAperture)]]
::jpeg::exifKeys
Returns a list of the EXIF keys which are currently understood. There may be keys present in
getExif data that are not understood. Those keys will appear in a 4 digit hexadecimal format.
::jpeg::removeExif file
Removes the Exif data segment from the specified file and replaces it with a standard JFIF
segment. Throws an error if file is not a JPEG image.
::jpeg::stripJPEG file
Removes all metadata from the JPEG file leaving only the image. This includes comments, EXIF
segments, JFXX segments, and application specific segments. Throws an error if file is not a JPEG
image.
::jpeg::getComments file
Returns a list containing all the JPEG comments found in the file. Throws an error if file is not
a valid JPEG image.
::jpeg::addComment file text...
Adds one or more plain text comments to the JPEG image in file. Throws an error if file is not a
valid JPEG image.
::jpeg::removeComments file
Removes all comments from the file specified. Throws an error if file is not a valid JPEG image.
::jpeg::replaceComment file text
Replaces the first comment in the file with the new text. This is merely a shortcut for
::jpeg::removeComments and ::jpeg::addComment Throws an error if file is not a valid JPEG image.
::jpeg::debug file
Prints everything we know about the given file in a nice format.
::jpeg::markers channel
This is an internal helper command, we document it for use by advanced users of the package. The
argument channel is an open file handle positioned at the start of the first marker (usually 2
bytes). The command returns a list with one element for each JFIF marker found in the file. Each
element consists of a list of the marker name, its offset in the file, and its length. The offset
points to the beginning of the sections data, not the marker itself. The length is the length of
the data from the offset listed to the start of the next marker.
LIMITATIONS
can only work with files cant write exif data gps exif data not parsed makernote data not yet implemented
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please
report such in the category jpeg of the Tcllib SF Trackers
[http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may
have for either package and/or documentation.
KEYWORDS
comment, exif, image, jfif, jpeg, thumbnail
CATEGORY
File formats
COPYRIGHT
Copyright (c) 2004-2005, Code: Aaron Faupell <afaupell@users.sourceforge.net> Copyright (c) 2007, Code: Andreas Kupries <andreas_kupries@users.sourceforge.net> Copyright (c) 2004-2009, Doc: Andreas Kupries <andreas_kupries@users.sourceforge.net> Copyright (c) 2011, Code: Pat Thoyts <patthoyts@users.sourceforge.net>