Jhead has no Graphical User Interface. Clicking on it with the mouse from Windows won't do anything for you - you have to use it from the Command prompt (or Dos prompt under Win95/98)
| -dt |
Delete thumbnails. Exif headers have a built-in thumbnail, which typically
occupies around 10k of space. As far as I can tell, this thumbnail is only used
by the digital cameras to display several really small thumbnails at a time. 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 the digicams. This command line option simply shortens the exif segment of the jpeg file so that the interesting settings are still in the camera.
-h
|
Displays summary of command line options.
| -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.
| -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).
| -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:
| jhead -model S100 *.jpg
I use this option to restrict my JPEG re-compressing to those images that came from my digicam, see the -cmd option.
-n
|
This option causes files with dates stored in the exif header to be renamed to the
file date. Renaming is restricted to files whose names consist largely of digits.
This effectively restricts renaming to files that have not already been manually renamed.
Use the -nf option to force renaming. | The file will be renamed to MMDD-HHMMSS. The year is not used for the file name (if you have images from that many different years together, you probably don't care enough about organizing your images to use this program. If you don't like it, you can always change the program. If the destination name is already in use (if another photo was taken at the exact same time by another camera), the times for next subsequent seconds are tried. This option is useful for naming jpegs of the same event taken from two cameras in such a way that they will appear in order in file managers and programs like Compupic or ACDSee. -nf
|
Same as '-n' but renames files regardless of original file name.
|
-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 re-inserted 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 Image-Magic'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 cannon 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:
jhead -cmd "jpegtran -progressive &i &o" -r *.jpg
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 generting program uses the exif tags to display the Jpeg images in order of taking.
-r
|
The recursive feature of version 1.0 never worked to my satisfaction, and I replaced it
with my recursive file globbing code in the Windows version. See below.
| |
jhead c:\pix\199*\*\*.jpg
This program goes one step beyond beyond that in that "**" as a path component means any
level of subdirectories. The invocation
jhead c:\**\*.jpg
will find ALL Jpegs files on the c: drive. The **
is only valid if it is the only path
component. For The path 'c:\a**\*.jpg'
will not recurse.
The '**'
recursive expansion is ONLY supportedd on the Windos version. The code is in the module 'myglob.c',
if you want to reuse it (I certainly intend to reuse that code for other applications)
Under Unix, the shell's wildcard expansion is
pretty decent already, and dealing with the convoluted nature of some Unix file layouts,
doing better would have been much more of a challenge.
There's a fancier version, with pre-built Windows binaries and a lossless cropping feature added at: http://sylvana.net/jpegcrop. I have a Compiled Windows Binary of Jpegtran on my website. I got this one by taking the source code for Jpegtran out of the RedHat 6.1 Linux distribution, and compiling it with Microsoft Visual C 5.0.