[KPhotoAlbum] More patches

Robert Krawitz rlk at alum.mit.edu
Sat Aug 15 16:01:39 BST 2015

On Sat, 15 Aug 2015 16:46:38 +0200, Johannes Zarl-Zierl wrote:
> ...resending because I was sending from the wrong address before..
> On Sunday 09 August 2015 11:03:34 Robert Krawitz wrote:
>> I don't really like the current lens EXIF logic.  On many Canon
>> cameras, Lens will work better than LensType.  For example, on the
>> 300D:
>> [1(rlk)|{!10}<dsl092-065-009>/altmnt/images/300d/dcim/101canon]
>> $ exiv2 -pa img_0108.jpg |grep Lens
>> Exif.CanonCs.LensType                        Short       1  (65535)
>> Exif.CanonCs.Lens                            Short       3  28.0 - 135.0 mm
> While using Exif.CanonCs.Lens may appear to be a "nicer" format than the value 65535, it actually has less information and might match other lenses that just happen to have the same zoom range. Therefore using Lens instead of LensType rather seems like a quick&dirty workaround to me.

If exiv2 can't translate the value (and 65535, or -1 for 16 bit
integers, looks like a default value that the camera inserts when it
has no other information), it's useless.  I'd rather have a generic
28-135 than a default value that applies to many lenses.

In this case, though, the problem is the camera.  The 300D is a very
old camera that didn't insert more modern EXIF data into the files.
It looks to me like it returns 65535 for all lenses.  Same for the
20D.  It wasn't until some time later (time between the 20D and the
7D) that Canon started inserting more meaningful LensType data.

For a body that doesn't have a meaningful LensType -- and I suspect if
you went back far enough you'd find older Nikons with the same issue
-- I'd rather get the generic lens focal length information than have
nothing meaningful.

> If you would be so kind and follow the instructions here:
> http://www.darktable.org/2015/02/on-lens-detection-and-correction/
> This would not only be a quick workaround, but allow _all_ programs
> using libexiv2 to show the full info on that lens.

See above why that doesn't apply in this case.
Robert Krawitz                                     <rlk at alum.mit.edu>

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