[KPhotoAlbum] EXIF (and equivalent META data for non-jpeg) creation date

[Andreas Neustifter]

Hi all,

since this can be a quite confusing topic I will write up my knowledge on
this matter (also for further reference...).

On 23.06.2010, at 13:00, Murray Strome wrote:

The one single piece of information that I would like to preserve in any
image is the "Date Taken", whether it is called Creation Date, or whatever.


There are two important dates that are treated separately: first there is
the creation date recorded by the camera in the EXIF data. Then there is the
modification date in the file system, this is initially set to the same date
as the creation date in the EXIF data.

The only exception would be if I choose to explicitly change it (e.g. with
EXIFTool or something similar). Provided nothing else were to change the
date, the only times I would want it changed would be:
1. The time/date was incorrectly set on the digital camera photo taken
2. The time/date was incorrectly changed by some operation
3. The photo was created by scanning a photo, and I know when it was taken

One of my greatest causes of frustration in organizing photos with
KPhotoAlbum (or any other tool) is that I find this date/time seems to get
changed so easily by almost anything I do with the photo. Even simply
copying it from one folder to another will often "mess up" the creation
date.


When copying a file usually the date of the copied file is set to the
current date. Sometimes graphical file managers (nautilus, k<something>) are
preserving the modification date; when copying a file in the command line
this can be achieved with the "-p" option (e.g. "cp -p <from> <to>"). A
simple copy does not modify the EXIF header (the file is an exact copy of
the original) so the EXIF creation date is unchanged.

For the case when the file date is wrong but the EXIF date is intact the
file modification time can be reset to match the EXIF date by several tools.
For jpg maybe the easiest is jhead with the "-ft" option (e.g. "jhead -ft
<file>.jpg"). For arbitrary files with embedded exif data exiftool can be
used (but I do not recall the option needed...).

When I use the GIMP to edit photos, this date is often changed to the date I
save the new version. Picasa sometimes REALLY messes up the date.


Most of the image editing software strips the EXIF data and when the file is
stored the modification date is set to the current date (which is the right
thing to do...). This is one of the reasons why it is _NEVER_ a good idea to
edit the original file. When the file is saved over the original file and
the software is asked to replace the current file then (usually) the EXIF
data is striped (and not available anymore) and the modification date is set
to current. Assuming this was the only copy the file creation date is lost
forever.

This can be prevented by _NEVER_ editing  the original image but first
copying the file and then editing the copy. The copy has then the wrong
modification date, but the original is still intact and the EXIF information
can be copied from the original to the copy and then also the modification
date of the copy can be set to the original creation date.
(E.g "jhead -te <orig>.jpg <edited-copy>.jpg" copies the EXIF data from the
original to the copy and "jhead -ft <edited-copy>.jpg" set the modification
date to the original creation date.)

If I can find a relatively easy way to fix the dates on the thousands of
photos that have already been changed (if only I could remember when they
were taken!), it will take me a LONG time to do so. In the meantime, is
there any advice on how to prevent the creation time/date from being
modified for new pictures? The only thing I can think of would be to learn
how to use EXIFTool to save all of the EXIF data from photos as I take them,
keep the information in whatever folder to which I copy them, then rewrite
the data from the file back to the photos.


As I said, it is a _VERY_ good idea to never modify the original (for
several reasons beside the EXIF data...); then it is always possible to use
the EXIF data from the original file.

This would entail a lot of work and already it takes to long to just rename
the photos to something more intelligible and to do some simple editing to
crop them and perhaps fix the colour balance.


Keeping the original is e.g. a good idea if you later visit a croped file
and decide that you do not like it you can revert to the original, make a
new copy and make a completely new edit. Since storage is (relatively) cheap
these days there is no excuse to not keep the original file anymore.

I notice that even those photos that I have taken in the past month have had
their dates changed. Some of the changes I can understand, such as from the
date the photo was taken to the date I edited it or copied it from one
computer to another. Others are a complete mystery. For example, some photos
I took on June 3 and 4 now show a creation date of May 30.


The only possibility for this is that you either
*) have the date not set properly on your machine,
*) have used a EXIF or file modification tool not properly
*) the file system is corrupt.

I can not imagine any reasonable workflow that reverts dates back beyond the
original creation date. You mentioned picasa, maybe this is faulty?

As others said earlier KPA does not change or modify files (besides invoking
a KIPI plugin), I guess that your problem is related to editing the original
files.

I hope this overview helps, I there are still questions open besides the
ones already answered in this list please ask away! (I hope thats okay for
the rest of the KPA folks...)

Andi
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