Re: [Libexif-devel] MakerNote support

[Lutz <lu...@us...>]

On Fri, 2002-11-08 at 07:25, Rod Whitby wrote:
> It seems that the MakerNote fields for the currently supported cameras
> (Canon, Olympus, and now Pentax) follow a pseudo-IFD structure, and I'm
> wondering if it would be useful to just add another entry into the IFD en=
um
> (EXIF_IFD_MAKER_NOTE), and then just re-use the existing exif_data_load_.=
..
> routines to load in the data (after any maker-specific prefix has been
> skipped over).

The problem is that most maker notes follow a _pseudo_-IFD structure.
That is, some screw up with the byte order, others with the offset,
others somewhere else... The code in exif-data will get unreadable.

Please keep libexif as close as possible to the standard. You can always
set up new objects like exif-mn-[entry,content,tag] (mn =3D MakerNote)
inheriting from the exif-equivalents.

For example, introduce=20

typedef struct _ExifMNContent ExifMNContent;
struct _ExifMNContent {
	ExifContent parent;

	/* Insert here whatever you like */
};

etc. and=20


and use this object like an ExifContent:

ExifMNContent *mn_content;
ExifMNEntry   *mn_entry;

ExifMNContent *
exif_mn_content_new (void) {
	ExifMNContent *mn_content;

	mn_content =3D malloc (sizeof (ExifMNContent));

	exif_content_init ((ExifContent *) mn_content);
}

void
exif_mn_content_some_function (ExifMNContent *mn_content) {

	ExifMNEntry *mn_entry;

        (...)
	exif_content_add_entry ((ExifContent *) mn_content,
                                (ExifEntry *) mn_entry));
}

> The only thing which needs to be handled specially is that
> the tags in the makernote are in a different namespace from the normal IF=
D

This is the case _now_. I wouldn't rely on manufacturers sticking to
that convention, as it isn't fixed in the spec.

> tags.  It would also mean that the existing interface for editing tags in
> the exif program can be re-used (you just specify a different IFD for
> makernote tags).

See above. I think keeping the MakerNote stuff separate leads to code
that is easier to maintain.

What do you think?

Lutz
--=20
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| Lutz M=FCller                 +49 (7156) 34837 |
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