On Sat, Mar 16, 2013 at 12:35 PM, Sebastian Kraft
<m...@sebastiankraft.net> wrote:
> > slr-tamron.xml: <model>Tamron 17-50mm f/2.8 XR Di II LD</model>
> >
> > Exif.PentaxDng.LensType Byte 4 Tamron AF
> > 17-50mm F2.8 XR Di-II LD (Model A16)
> >
> > So the problem seems to be the Model A16 suffix :(
> >
> > So looking into the Exiv2 sources:
> >
> > { 0x04e6, "Tamron SP AF 17-50mm F2.8 XR Di II" },
> > { 0x07e6, "Tamron AF 17-50mm F2.8 XR Di-II LD (Model A16)" },
> >
>
> In this particular case: are these different lenses? Or are there just
> two different names for one single lens?
In this particular case, it's likely the same lens.
> > So to be honest I'm not sure how to proceed with this.... I'm tempted
> > to think this should be resolved on lensfun's end with aliases instead
> > of fuzzy matching....
> >
> > The temporary workaround would be to create a local """alias""" by
> > copying the lensfun entry with a different name.
>
> The problem I see is that an exact lens name search will never work.
> AFAIK the lens name is not directly stored in EXIF data but just a lens
> ID. This lens ID is resolved by the EXIF reader to a human readable
> name. So the exact name highly depends on the underlying EXIF library.
Exactly, this may even differ between libraries.
> I don't think it's a good solution to introduce aliases in the lensfun
> database. This would end up in adding aliases for every single exif
> library.
Exactly.
> Ok, currently most open source projects use exiv2 but even in
> this case, as soon as exiv2 changes some lens names we have to adjust
> the database. There will always be lenses that won't exactly match the
> name in the database anyway. So from my point of view it should be up to
> the application and user interface to finally let the user check if the
> preselected lens is correct. An auto selection and correction based on
> lens exif data will never work reliably.
Just aliasing all the Exiv2 names will make autoselection work in most
practical cases though.
> For example Darktable could automatically select the correct profile in
> it's GUI but the user would have to manually enable the lens correction
> tool to apply the changes.
Without aliasing, autoselection will fail often, and enabling lens
correction is already optional, it's not enabled by default.
The problem with fuzzy autoselect remains, that we could accidentally
autoselect the wrong lens, where the user does not notice the wrong
correction is being applied. So I failure to properly correct,
actually becomes adding imaging defects.
And it is very nice, that enabling 'lens correction' is pretty much
all you have to do for it to work. The lens correction ui should be
primarily for special case handling in my view.
Regardless, this is a discussion that primarily needs to be hand with
the lensfun maintainers.
Regards,
Pascal de Bruijn
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