LEADTOOLS Raster Imaging Features > Markers and Comments > Notes on Exif Data Types

Notes on Exif Data Types

The Exif standard defines the following data types for comments. Usage is dependent of your development system. To see the usage, refer to the code example for your system.

Data type	Description
UNDEFINED	The data type is determined by the field.
SHORT	Integer.
LONG	Long integer.
ASCII	Character string.
BYTE	Array of bytes.
RATIONAL	An array of two unsigned long integers that express a fraction. The first value is the numerator, and the second is the denominator. (Visual Basic does not recognize unsigned long integers and will interpret large values, as negative values.)
SRATIONAL	An array of two signed long integers that express a fraction. The first value is the numerator, and the second is the denominator.

The length of a comment is based on the data type. For example, an SRATIONAL with a length of 3 is an array of 6 long integers.

When you set a comment that requires an array, the array can be zero-based or 1-based (where the first element has an index of 1). When you get a comment that is an array, it will always be zero-based (where the first element has an index of 0).

When you assign comments, the ActiveX does data type conversions for you. For example, if a comment is a RATIONAL with a length of 3, you can assign an array of six integers. If you assign an invalid value, the value is ignored.