Re: [Libexif-devel] [patch] accessors for maker notes

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

On Tue, May 26, 2009 at 10:16:24AM -0700, Jeff Breidenbach wrote:
> I'm submitting this patch on behalf of Lance Huang.  It adds two
> functions to access the entries in maker notes. Patch is against the
> current CVS tree; please consider integrating. Thanks!

Giving access to makernote tags is problematic to do consistently for all
current and potential future makernote formats. The biggest problem is
that they can take on absolutely any format--by definition, it's up
to the manufacturer. So, assuming the same format as the regular EXIF
tags isn't sufficient. Even those manufacturers that do use notes
that look just like EXIF tags could create a camera in the future that
expands the range of standardized fields like ExifFormat, for example. 
And how to give access to tags from cameras that don't use a TLV scheme?
How about cameras (like Olympus) that can have sub-IFDs within their
MakerNotes? libexif right now takes advantage of this inconsistency by
doing extra parsing on some tags (e.g. for Canon) to make them easier
to handle by the user, although that destroys the ability to access the
unadulterated tags.

Also, the gaping hole in the API whereby libexif doesn't say which kind of
makernote format is being returned needs to be addressed.

These issues all should be addressed before giving access to raw
makernote tags. The approach in the patch is also inconsistent with
the way libexif gives access to normaltags right now. Better would be
to use an approach like that around the ExifEntry structure.  

Adding this kind of access to makernotes is useful so I hope someone
manages to resolve all these issues.

>>> Dan
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