[Libexif-devel] Using MakerNote tags

[Dan F. <da...@co...>]

I think I've spotted a hole in the libexif API when it comes to MakerNote
tags. There doesn't seem to be any way for the application to know the
type (manufacturer) of the MakerNote it's dealing with using the
exif_mnote_* functions.  That means that it's difficult to reliably
extract information for a known type of MakerNote.

For example, if an app wants the contents of the Canon "Owner name" MakerNote
tag (9), there's no way of knowing if a "9" returned from
exif_mnote_data_get_id() is the Canon "Owner name" or some other MakerNote
tag, such as the Nikon "Flash Mode".

I think what needs to be done is to make the enum ExifDataTypeMakerNote
public and add a exif_mnote_data_type() function that just internally calls
exif_data_get_type_maker_note(). That will provide the MakerNote tag
namespace information to the caller and provide context for the exif_mnote_*
functions.

One could argue that an app should be looking at the EXIF "Manufacturer" tag
to determine this. That's a reasonable request, but many manufacturers use
the same MakerNote style (e.g. Olympus, Sanyo, Nikon) and it would be neat
if apps would automatically obtain support for a new manufacturer's
MakerNotes. Hard-coding "Olympus", "Sanyo", "Nikon" in the app means that
when some future "Xyzzy" manufacturer starts using that style of tag, the app
must be modified.  But maybe this is low-level and nonstandardized enough
to force apps to do just that.

>>> Dan
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