Exif headers are really a write only format, seeing that the binary blob
also contains data of unknown and unspecified format for the manufacturer
data.
As such, the dt option isn't entirely safe. I can't fix that.
Matthias
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Friday, December 03, 2010 11:27 AM
Subject: Bug#605804: mention -dt also wipes up tons of padding, often many
more bytes than the thumbnail itself!
X-debbugs-Cc: [email protected]
Package: jhead
Version: 1:2.90-2
Severity: wishlist
File: /usr/share/man/man1/jhead.1.gz
-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.
Also mention that it also mops up surrounding wasteful padding*. E.g.,
here's a before and after of jhead -v output after a jhead -dt operation:
-Exif header 35397 bytes long
+Exif header 4604 bytes long
- ThumbnailLength = 5351
+ ThumbnailLength = 0
As we see, we saved not only 5351 bytes, but 35397 - 4604 = 30793 !
*Actually I'm not sure what it was. By the way, there should be a option
that extracts the exif header to stdout so one can examine it.
jhead -v should mention padding sections too.
P.S. the author's (already obfuscated) email address appears in many less
places than his
name, and must be dug up. Why not put it also on each place...
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