.TH JHEAD 1 "04 Oct 2008" "jhead 2.84"
.SH NAME
jhead \- Digicam JPEG Exif header manipulation tool
.SH SYNOPSIS
.B jhead
[
.I options
]
[
.I file\.\.\.
]

.LP
.SH DESCRIPTION
.LP
.B jhead
is used to display and manipulate data contained in the Exif header of JPEG
images from digital cameras.  By default, jhead displays the more useful
camera settings from the file in a user-friendly format.
.PP
.B jhead
can also be used to manipulate some aspects of the image relating to JPEG and
Exif headers, such as changing the internal timestamps, removing the thumbnail,
or transferring Exif headers back into edited images after graphical editors
deleted the Exif header.
.B jhead 
can also be used to launch other programs, similar in style to the UNIX
.B find 
command, but much simpler.


.SH GENERAL METADATA OPTIONS
.TP
.BI \-\^te \ file
Transplant Exif header from a JPEG (with Exif header) in 
.I file
into the image that is manipulated.  This option is
useful if you like to edit the photos but still want the Exif header on your photos.
As most photo editing programs will wipe out the Exif header, this option can be used
to re-copy them back from original copies after editing the photos.


This feature has an interesting 'relative path' option for specifying the 
thumbnail name.  Whenever the <name> contains the characters '&i', jhead 
will substitute the original  filename for this name. This allows creating a 
'relative name' when doing a whole batch  of files. For example, the 
incantation:

.B jhead -te "originals\&i" *.jpg

would transfer the exif header for each .jpg file in the originals directory by 
the same name, Both Win32 and most Unix shells treat the '&' character in a 
special way, so you have to put quotes around that command line option for the 
'&' to even be passed to the program.

.TP
.B \-dc
Delete comment field from the JPEG header.  Note that the comment
is not part of the Exif header.
.TP
.B \-de
Delete the Exif header entirely.  Leaves other metadata sections intact.
.TP
.B \-di
Delete the IPTC section, if preent.  Leaves other metadata sections intact.
.TP
.B \-dx
Delete the XMP section, if preent.  Leaves other metadata sections intact.
.TP
.B \-du
Delete sections of jpeg that are not Exif, not comment, and otherwise not 
contributing to the image either - such as data that photoshop might leave in the image.
.TP
.B \-purejpg
Delete all JPEG sections that aren't necessary for rendering the image.  Strips any
metadata that various applications may have left in the image.  A combintion of 
the -de -dc and -du options.
.TP
.B \-mkexif
Creates minimal exif header. Exif header contains date/time, and empty thumbnail 
fields only. Date/time set to file time by default. use with -rgt option if you 
want the exif header to contain a thumbnail. Note that exif header creation is 
very limited at this time, and no other fields can be added to the exif header 
this way.
.TP
.B \-ce
Edit the JPEG header comment field (note, this comment field is outside the Exif structure
and can be part of Exif and non Exif style JPEG images).

A temporary file containing the comment is created and a text editor is launched to edit
the file.  The editor is specified in the EDITOR environment variable.  if none is specified
notpead or vi are used under Windows and Unix respectively.  After the editor exits,
the data is transferred back into the image, and the temporary file deleted.
.TP
.BI \-\^cs \ file
Save comment section to a 
.I file
.TP
.BI \-\^ci \ file
Replace comment with text from
.I file
.TP
.BI \-\^cl \ string
Replace comment with specified string from command line
.IR file



.SH DATE / TIME MANIPULATION OPTIONS

.TP
.B \-ft
Sets the file's system time stamp to what is stored in the Exif header.
.TP
.B \-dsft
Sets the Exif timestamp to the file's timestamp. Requires an Exif header to 
pre-exist. Use -mkexif option to create one if needed.
.TP
.BI \-\^n [format_string]
This option causes files to be renamed using the date information from the Exif header 
"DateTimeOriginal" field.
If the file is not an Exif file, or the DateTimeOriginal does not contain a valid value,
the file date is used.
Renaming is by default restricted to files whose names consist largely of digits.
This effectively restricts renaming to files that have not already been manually renamed, as
the default sequential names from digital cameras consist largely of digits.
Use the 
.B -nf 
option to force renaming of all files.

If the 
.I format_string
is omitted, the file will be renamed to MMDD-HHMMSS.  Note that 
this scheme doesn't include the year (I never have photos from different years together anyway).

If a 
.I format_string
is provided, it will be passed to the strftime function as the format string.  
In addition, if the format string contains '%f', this will
substitute the original name of the file (minus extension).  '%i' will substitute a sequence
number.  Leading zeros can be specified like with printf - i.e. '%04i' pads the number to 4 
digits using leading zeros.

If the target name already exists, the name will be appended with "a", "b", "c", etc,
unless the name ends with a letter, in which case it will be appended with "0", "1", "2", etc.

This feature is especially useful if more than one digital camera was used to take pictures
of an event.  By renaming them to a scheme according to date, they will automatically
appear in order of taking in most directory listings and image browsers.  Alternatively,
if your image browser supports listing by file time, you can use the -ft option to set
the file time to the time the photo was taken.

Some of the more useful arguments for strftime are:

.BR %H \ Hour\ in\ 24-hour\ format\ (00\ -\ 23)
.br
.BR %j \ Day\ of\ year\ as\ decimal\ number\ (001\ -\ 366)
.br
.BR %m \ Month\ as\ decimal\ number\ (01\ -\ 12)
.br
.BR %M \ Minute\ as\ decimal\ number\ (00\ -\ 59)
.br
.BR %S \ Second\ as\ decimal\ number\ (00\ -\ 59)
.br
.BR %w \ Weekday\ as\ decimal\ number\ (0\ -\ 6;\ Sunday\ is\ 0)
.br
.BR %y \ Year\ without\ century,\ as\ decimal\ number\ (00\ -\ 99)
.br
.BR %Y \ Year\ with\ century,\ as\ decimal\ number

Example:

.B jhead -n%Y%m%d-%H%M%S *.jpg
This will rename files matched by *.jpg in the format YYYYMMDD-HHMMSS

For a full listing of strftime arguments, look up the strftime in them man pages.  
Note that some arguments
to the strftime function (not listed here) produce strings with characters such as '/' and ':' that
may not be valid as part of a filename on various systems.

.TP
.B \-nf
Same as '-n' but renames files regardless of original file name.


.TP
.B \-ta<+|-><timediff>
Adjust time stored in the Exif header by h:mm backwards or forwards.  Useful when having
taken pictures with the wrong time set on the camera, such as after travelling across
time zones, or when daylight savings time has changed.

This option changes all Date/time fileds in the exif header, including "DateTimeOriginal" (tag 0x9003) 
and "DateTimeDigitized" (tag 0x9004).
.TP
.B \-da<newdate>-<olddate>

Works like -ta, but for specifying large date offsets, to be used when fixing dates from 
cameras where the date was set incorrectly, such as having date and time reset by battery
removal on some cameras

Because different months and years have different numbers of days in them, a simple offset
for months, days, years would lead to unexpected results at times.  The time offset is
thus specified as a difference between two dates, so that jhead can figure out exactly
how many days the timestamp needs to be adjusted by, including leap years and daylight
savings time changes.
The dates are specified as yyyy:mm:dd.  For sub-day adjustments, a time of day can also
be included, by specifying yyyy:nn:dd/hh:mm or yyyy:mm:dd/hh:mm:ss

Examples:

Year on camera was set to 2005 instead of 2004 for pictures taken in April
.br
jhead -da2005:03:01-2004:03:01

Default camera date is 2002:01:01, and date was reset on 2005:05:29 at 11:21 am
.br
jhead -da2005:05:29+11:21-2002:01:01
.TP
.B \-ts
Sets the time stored in the Exif header to what is specified on the command line.
Time must be specified as:
.I yyyy:mm:dd-hh:mm:ss
.TP
.B \-ds
Sets the date stored in the Exif header to what is specified on the command line.
Can be used to set date, just year and month, or just year.
Date is specified as: 
.I yyyy:mm:dd,  yyyy:mm, or yyyy


.SH THUMBNAIL MANIPULATION OPTIONS

.TP
.B \-dt
Delete thumbnails from the Exif header, but leave the
interesting parts intact.  This option truncates the thumbnail from the Exif header, provided
that the thumbnail is the last part of the Exif header (which so far as I know is always the case).
Exif headers have a built-in thumbnail, which typically
occupies around 10k of space.  This thumbnail is used by digital cameras.  Windows XP may also
use this thumbnail if present (but it doesn't need it).  The
thumbnails are too small to use even full screen on the digicam's LCD.
I have not encountered any adverse side effects of deleting the thumbnails, even from the
software provided with my old Olympus digicam.  Use with caution.

.TP
.BI \-\^st \ file
Save the integral thumbnail to 
.I file
The thumbnail lives
inside the Exif header, and is a very low-res JPEG image.  Note that making
any changes to a photo, except for with some programs, generally wipes out the Exif header
and with it the thumbnail.

The thumbnail is too low res to really use for very much.

This feature has an interesting 'relative path' option for specifying the thumbnail name.
Whenever the name for 
.I file 
contains the characters  '&i',
.B jhead 
will substitute the original
filename for this name.  This allows creating a 'relative name' when doing a whole
batch of files.  For example, the incantation:

.B jhead -st "thumbnails/&i" *.jpg

would create a thumbnail for each .jpg file in the thumbnails directory by the same name,
(provided that the thumbnails directory exists, of course).
Both Win32 and UNIX shells treat the '&'character in a special way, so you have to
put quotes around that command line option for the '&' to even be passed to the program.

If a '-' is specified for the output file, the thumbnail is sent to stdout. (UNIX build only)

.TP
.B \-rt
Replace thumbnails from the Exif header.
This only works if the exif header already contains a thumbnail, and the thumbnail is at the
end of the header (both always the case if the photo came from a digital camera)
.TP
.BI \-\^rgt \ size
Regnerate exif thumbnail.
'size' specifies maximum height or width of thumbnail.
Relies on 'mogrify' program (from ImageMagick) to regenerate the thumbnail.
This only works if the image already contains a thumbail.  

.SH ROTATION OPTIONS
.TP
.B \-autorot
Using the 'Orientation' tag of the Exif header, rotate the image so that it is upright. 
The program 
.B jpegtran 
is used to perform the rotation. This program is present in most 
Linux distributions.  For windows, you need to get a copy of it.  After rotation, the 
orientation tag of the Exif header is set to '1' (normal orientation).  The thumbnail 
is also rotated. Other fields of the Exif header, including 
dimensions are untouched, but the JPEG height/width are adjusted.
This feature is especially useful with newer Canon cameras, that set the orientation 
tag automatically using a gravity sensor.
.TP
.B \-norot
Clears the rotation field in the Exif header without altering the image.  Useful if
the images were previously rotated without clearing the Exif rotation tag, as some
image browsers will auto rotate images when the rotation tag is set.
Sometimes, thunbails and rotation  tags can get very out of sync from manipulation
with various tools.  To reset it all use -norot with -rgt to clear this out.

.SH OUTPUT VERBOSITY CONTROL
.TP
.B \-h
Displays summary of command line options.
.TP
.B \-v
Makes the program even more verbose than it already is.  Like DOS programs, and unlike
UNIX programs, Jhead gives feedback as to what it is doing, even when nothing goes wrong.
Windows user that I am, when something doesn't give me feedback for 20 seconds, I assume
its crashed.
.TP
.B \-q
No output on success, more like Unix programs.
.TP
.B \-V
Print version info and compilation date.
.B \-exifmap
Show a map of the bytes in the exif header. Useful when analyzing strange exif headers, 
not of much use to non software developers.
.TP
.B \-se
Suppress error messages relating to corrupt Exif header structure.
.TP
.B \-c
Concise output.  This causes picture info to be summarized on one line instead of several.
Useful for grep-ing through images, as well as importing into spread sheets (data is space
delimited with quotes as text qualifier).

.SH FILE MATCHING OPTIONS
.TP
.B \-model
Restricts processing of files to those whose camera model, as indicated by the Exif image
information, contains the substring specified in the argument after '-model'.
For example, the following command will list only images that are from an S100 camera:

.B jhead -model S100 *.jpg

.B jhead -model S100 *.jpg

I use this option to restrict my JPEG recompensing to those images that came from my 
Cannon S100 digicam, (see the -cmd option).
.TP
.B \-exonly
Skip all files that don't have an Exif header.  Photos straight from a digital camera
have an Exif header, whereas many photo manipulation tools discard the Exif header.
.TP
.B \-cmd
Executes the specified command on each Jepg file to be processed.

The Exif section of each file is read before running the command, and reinserted
after the command finishes.

The specified command invoked separately for each JPEG that is processed, even if
multiple files are specified (explicitly or by wild card).
I use this option to process whole directory trees of JPEGs from my digital camera
with jpegtran (Independent JPEG group) and ImageMagick's 'MOGRIFY' command without 
loosing the camera settings and other info stored in the Exif headers.

jpegtran is useful for lossless rotation, as well as for converting JPEGs to
progressive JPEGs (also a lossless process, but results in typically 5% smaller files)
I use mogrify for re-compressing the images I get from my Canon PowerShot S100 to
80% quality.  The Canon JPEGs are either way too 'high quality' for the resolution, or
are suboptimally encoded.  Using mogrify to 80% produces no detectable loss in quality,
with files about half the size.

Example use:

Having a whole directory tree of photos from my S100, I run the following commands:

.B jhead -cmd "mogrify -quality 80 &i" -model S100 -r *.jpg
.br
.B jhead -cmd "jpegtran -progressive &i > &o" -r *.jpg

The first command mogrifies all JPEGs in the tree that indicate that they are from a 
Cannon S100 in their Exif header to 80% quality at the same resolution.  This is a 'lossy'
process, so I only run it on files that are from the Canon, and only run it once.
The next command then takes a JPEGs and converts them to progressive JPEGs.  The result
is the same images, with no discernible differences, stored in half the space.  This only
produces substantial savings on some cameras, such as the Canon S100.  The newer S110 and S300
cameras are smarter about how they compress JPEG images, so re-mogrifying them may not give
you any savings unless you crank the quality way down.  However, turning them into progressive
JPEG images is a lossless process that typically makes image files 5% smaller.

Keeping the Exif header information is important to me, as I like to check things like the
shutter speed for some of my photos, and my HTML index generating program uses the Exif tags
to display the JPEG images in order of taking.

.SH SEE ALSO
.BR jpegtran (1),
.BR mogrify (1),
.BR rdjpgcom (1),
.BR wrjpgcom (1)
.SH AUTHOR
Matthias Wandel
.SH BUGS
After jhead runs a program to rotate or resize an image, the image dimensions and thumbnail 
in the Exif header are not adjusted.
.PP
Modifying of Exif header data is very limited, as Jhead internally only has a read only
implementation of the file system contained in the Exif header.  For example, there is no way
to replace the thumbnail or edit the Exif comment in the Exif header.  There is also no way
to create minimal exif headers.
.PP
Some Canon digital SLR cameras fail to adjust the effective sensor resolution when shooting at less
than full resolution, causing jhead to incorrectly miscalculate the sensor width and 35mm equivalent 
focal length.  The same can result from resizing photos with Photoshop, which will manipulate
parts of the exif header.
This is often reported as a bug in Jhead, but Jhead can't do much about incorrect data.
.PP
Send bug reports to mwandel at sentex dot net.

.SH COPYING PERMISSIONS
Jhead is 'public domain'.  You may freely copy jhead, and reuse part or all of its code 
in free or proprietary programs.   I do however request that you do not post my e-mail
address in ways that spam robots can harvest it.