Implementing TIFF Comments and Tags

Initially, only TIFF files supported TIFF tags. But the TIFF tags are so flexible and well documented that other formats added mechanisms for including TIFF tags:

The TIFF file formats support a number of comments that are saved and loaded using predefined tags. To specify a comment to be saved, you can use the LFileSettings::SetComment and LFileSettings::GetComment functions. To read a comment from an existing file, you can use LFile::ReadComment or LMemoryFile::ReadComment. To read a comment from a file at a specified location, use the LFile::ReadCommentOffset function. To read all the comment fields stored in a file, use LFile::ReadComments. To free the data allocated by calling the LFile::ReadComments function, use LFile::FreeComments.

NOTE: If an error occurred in reading all file comments using the LFile::ReadComments function, then no comments will be returned, and the user is responsible to find the valid metadata in the file.

For a list of possible comments, refer to TIFF File Comments.

If the comments do not meet your needs, you can define your own tag for saving additional non-raster data in a TIFF file. For example, you may want to define a tag to save annotations.

The TIFF 6.0 Specification sets aside a range of private tags that developers can define. To avoid conflicts with files created by other developers, you can register your tag by contacting Adobe Developer Relations. (The E-Mail address posted on The Unofficial TIFF Home Page is gapdevsup@adobe.com.)

To define a tag and to specify the data to save in the tag, you can use the LFileSettings::SetTag and LFileSettings::GetTag functions. To load the tagged data from a file, you can use LFile::ReadTag, LFile::ReadTags, or LMemoryFile::ReadTag. To read all the tags stored in a file, use LFile::ReadTags. To free the data allocated by calling the LFile::ReadTags function, use LFile::FreeTags. To write tags to an existing file, or to change existing tags in a file, use LFile::WriteTag.

NOTE: To write tags to a TIFF file, use LFile::WriteTag instead of using LFileSettings::SetTag followed by LFile::Save or LMemoryFile::Save.

LFile::EnumTags enumerates all tags in a TIFF, Exif or HEIC/HEIF file. For each tag enumerated, the LFile::EnumTagsCallBack function is called. Through this callback function, you can obtain information about, or otherwise process, each tag that is enumerated. You can delete a specified tag from the file using LFile::DeleteTag.

The LEADTOOLS functions let you save one additional tag in a TIFF file. They are designed for future expansion to more than one tag.

NOTE: To save a region inside a TIFF file, you must have an unlocked Document, Vector, or Medical Imaging license

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