Claudio Santambrogio

jhead

Sunday, January 14, 2007 12:19:02 AM

…is a small, simple but powerfull command line application, primarily thought as a tool for viewing, extracting, handling or modifying EXIF data in images - and extremely useful for preparing your picture collections.

After downloading the pics from my camera, I first lowercase all files (never really got why digital cameras all save in uppercase) and then run

jhead -autorot *.jpg

to autorotate all images according to their EXIF tag. After this, the orientation tag is set to "1" (which is normal orientation), in order to avoid rotating it once more in case you'd run the command again.

Jpeg images contain, among their EXIF data, also thumbnails, used by digital cameras to preview the image on their LCD display. It is trivial to extract them:

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

where thumbnails/ is a directory previously created, to contain the thumbnails; and the variable &i tells jhead to use the image's name for the thumbnail.

Et voilà…

jhead has a plethora of options for more advanced usage, and your needs might be different than mine - so I'll leave them to you to discover…

Incidentally, the author of jhead is the very same guy who built his own home pipe organ.

apache configure problemunleash the powers

Comments

Dan Alexandrudantesoft # Sunday, January 14, 2007 1:02:58 AM

Are you sure all digital cameras generate thumbnails in the (Exif flavour of) Jpeg files ?

RamūnasRamunas # Sunday, January 14, 2007 8:18:02 AM

You're my hero, just yesterday I got a camera with position sensor, and I was thinking about writing an app which would rotate the images for me myself. Thanks

Claudio Santambrogiocsant # Sunday, January 14, 2007 8:54:34 AM

dantesoft, thumbnails are part of the EXIF spec (which, admittedly, is a mess), and AFAIK all modern cameras do add the thumbnail. They are small and take about 10K. Of course jhead can also remove them from the image. Some cameras add also a second, larger, thumbnail to the image itself (and not the metadata)! This is due to size restrtictions of the metadata in an image.