[Libexif-devel] Incorrect calculation of APEX values

[Jef D. <jef...@ho...>]

Several exif tags related to exposure (shutter speed, aperture value and
brightness) are stored as apex values. Inside libexif, these values are
calculated incorrectly. The formulas should be inverted to produce the
correct results.

I have attached a patch to fix this bug. With my patch, both the APEX
value (in EV units) and the converted value is shown. But it's trivial
to change that, if required.

I introduced some new functions to make the conversions. I used the same 
functions already in my patch for the canon makernotes some time ago. So 
it could be useful to move them to a central place (e.g. exif-apex.[ch] 
files) instead of duplicating them.