Makernote is a standard EXIF tag of UNDEFINED (byte) type. This tag usually is used as a "hidden" IFD. Makernote can not be read in and written out as a BLOB, because IFD offsets become invalid. Therefore, to preserve this tag while writing an image it's necessary to decode it during reading and re-encode it during writing, despite the fact that formally makernote is just a binary tag.

There are several types of makernotes, all of them have corresponding constants in Metadata.h file:

To present Makernote info in a convenient way ImageGear introduces a special structure as an addition to the standard EXIF Metadata: "Makernote*s* Wrapper IFD". Instead of a single binary Makernote*s* tag (37500), we are adding a virtual IFD, containing all the information about Makernote*s*.

'MakerNote Wrapper IFD' has the following format depending on the 'type' tag:

• Type IG_MAKERNOTE_TYPE_UNKNOWN:

  	Copy Code
  'MakerNote wrapper IFD' -------->'type' = IG_MAKERNOTE_TYPE_UNKNOWN -------->'binary MakerNote'

• Type IG_MAKERNOTE_TYPE_IFD:

  	Copy Code
  'MakerNote wrapper IFD' -------->'type' = IG_MAKERNOTE_TYPE_IFD -------->'MakerNote IFD' ----------------> 'individual MakerNote tag 1' ----------------> 'individual MakerNote tag 2' ... ----------------> 'individual MakerNote tag N' -------->'binary MakerNote'

• Type IG_MAKERNOTE_TYPE_IFD_PREFIXED:

  	Copy Code
  'MakerNote wrapper IFD' -------->'type' = IG_MAKERNOTE_TYPE_IFD_PREFIXED -------->'MakerNote IFD prefix' -------->'MakerNote IFD' ----------------> 'individual MakerNote tag 1' ----------------> 'individual MakerNote tag 2' ... ----------------> 'individual MakerNote tag N' -------->'binary MakerNote'

• Type IG_MAKERNOTE_TYPE_TIF_HEADER_PREFIXED:

  	Copy Code
  'MakerNote wrapper IFD' -------->'type' = IG_MAKERNOTE_TYPE_TIF_HEADER_PREFIXED <The rest of the structure is identical to IG_MAKERNOTE_TYPE_IFD_PREFIXED>

• Type IG_MAKERNOTE_TYPE_IFD_PREFIXED_OFFSET_II:

  	Copy Code
  'MakerNote wrapper IFD' -------->'type' = IG_MAKERNOTE_TYPE_IFD_PREFIXED_OFFSET_II <The rest of the structure is identical to IG_MAKERNOTE_TYPE_IFD_PREFIXED>

If 'Makernote' EXIF tag is present in the file then ImageGear will always provide it in its original binary form via metadata callback ('binary Makernote' tag) on the read side, and will also optionally provide it as a decoded sub-IFD (w/ or w/o prefix depending on how it is stored in the original file) if it can be decoded.

ImageGear will ignore 'binary Makernote' tag on the write side for the 'Makernote wrapper IFDs' that have 'type' other than IG_MAKERNOTE_TYPE_UNKNOWN - and construct 'Makernote' EXIF tag based on the 'Makernote IFD'.

ImageGear will store 'binary Makernote' to file 'as is' for the 'Makernote wrapper IFDs' that have 'type' set to IG_MAKERNOTE_TYPE_UNKNOWN.

If 'Makernote wrapper IFD' is not provided to ImageGear during saving operation then 'Makernote' EXIF tag will not be saved into the output file.

Makernote IFD tags are listed below:

Custom Makernote Tags and IFDs

The following custom tags and IFDs are introduced for Makernote support:

Makernote Wrapper IFD: tag = 37500 (same as standard Makernote tag). This IFD is located in the "Exif IFD" (34665).

New tags, which belong to the Makernote Wrapper IFD:

enum enumIGEXIFMakerNoteTagIDs
{
IGMDTAG_ID_EXIF_MAKERNOTE_TYPE = 1,
IGMDTAG_ID_EXIF_MAKERNOTE_PREFIX = 2,
IGMDTAG_ID_EXIF_MAKERNOTE_BINARY = 1000,
IGMDTAG_ID_EXIF_MAKERNOTE_DATA_IFD = 1001
};

Vendors and Models Currently Supported

©2016. Accusoft Corporation. All Rights Reserved.