# jpeg(3tcl) 0.5 jpeg "JPEG image manipulation"

## Name

jpeg - JPEG querying and manipulation of meta data

## Synopsis

- package require Tcl 8.2
- package require jpeg ?0.5?

- ::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.

  Attention: It is the resonsibility of the caller to close the channel after its use.

::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 Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## Keywords

comment, exif, image, jfif, jpeg, thumbnail

## Category

File formats

## Copyright

Copyright © 2004-2005, Code: Aaron Faupell <afaupell@users.sourceforge.net>
Copyright © 2007, Code: Andreas Kupries <andreas_kupries@users.sourceforge.net>
Copyright © 2004-2009, Doc: Andreas Kupries <andreas_kupries@users.sourceforge.net>
Copyright © 2011, Code: Pat Thoyts <patthoyts@users.sourceforge.net>