Playing with exif

Exif information is most commonly encountered in pictures from digital cameras. I don’t have a lot of requirements surrounding exif, just the following:

First Go

I had been using jpegtran to rotate my jpegs, and then jhead to update the mtime. I wasn’t totally happy with jhead in particular, because it seems too windowsy and not very complete. Anyway, image rotation worked well with jpegtran -rotate 90 etc, and jhead did its job: jhead -ft image.jpg sets the mtime to what exif says, and jhead -de image.jpg deletes the header altogether. But there are better solutions!

exiftran

Exiftran is a part of fbida. I stumbled across it and discovered that, unlike jpegtran, it updates the exif information. So now my image rotation commands are:

Rotate 270 degrees (ie anti-clockwise):

% exiftran -2 -o rotated.jpg original.jpg

Rotate 180 degrees

% exiftran -1 -o rotated.jpg original.jpg

Rotate 90 degrees (ie clockwise)

% exiftran -9 -o rotated.jpg original.jpg

And the one I like the best:

Rotate automatically based on the exif rotation tag

% exiftran -a -o rotated.jpg original.jpg

Exiftran can also fix up the mess jpegtran left behind, by using the -ni switch (to not rotate the jpeg, but still rotate the thumbnail and update the rotation tag). The -i switch tells exiftran to write the rotated image out to the original filename, and -p tells it to keep the original mtime when using -i. Someday I may stop using gqview for rotation altogether, and simply do

% exiftran -aip *.jpg

exiv2

Exiv2 is a program and library for manipulating the exif header. And it doesn’t just work on jpegs, but on any file with exif, such as TIFFs and RAW files. exiv2 is a complicated beast. The options to solve my problems are:

Set the mtime of the file to the exif creation time (like the old jhead -ft did).

% exiv2 mv -T abc.jpg

Copy the exif headers from the Nikon RAW files in /tmp to the correspondingly named jpegs in /data. Not all the exif data makes sense, since the RAW file has been converted to a jpeg, but as far as I’m concerned, it’s close enough. I mostly need the time, and possibly the aperture and shutter speed etc., and that’s all still valid.

% exiv2 in -k -l /tmp -S .nef /data/*.jpg

Remove exif headers from the jpeg file.

% exiv2 rm *.jpg

Hex Editor

Neither jhead nor exiv2 can cope with the timestamp used by one of my cameras when there camera’s date hasn’t been set. I have this problem because somehow the camera forgot the date and time and took a bunch of photos without them. As a result I’ve been getting this message:

Failed to parse or convert timestamp +0000:00:00 00:00:00

Goodness knows why none of these programs can only adjust the date, rather than setting it. Anyway, I’ve been able to solve the problem using a hex editor. Thankfully the timestamps (there are 3 of them) are quite easily found and edited in plain text.