JEITA CP-3451
- 14 -
Tag
Each tag is assigned a unique 2-byte number to identify the field. The tag numbers in the Exif 0th IFD and 1st IFD
are all the same as the TIFF tag numbers.
Type
The following types are used in Exif:
1 = BYTE
An 8-bit unsigned integer.,
2 = ASCII
An 8-bit byte containing one 7-bit ASCII code. The final byte is terminated with NULL.,
3 = SHORT
A 16-bit (2-byte) unsigned integer,
4 = LONG
A 32-bit (4-byte) unsigned integer,
5 = RATIONAL
Two LONGs. The first LONG is the numerator and the second LONG expresses the
denominator.,
7 = UNDEFINED
An 8-bit byte that can take any value depending on the field definition,
9 = SLONG
A 32-bit (4-byte) signed integer (2's complement notation),
10 = SRATIONAL
Two SLONGs. The first SLONG is the numerator and the second SLONG is the
denominator.
Count
The number of values. It should be noted carefully that the count is not the sum of the bytes. In the case of one
value of SHORT (16 bits), for example, the count is '1' even though it is 2 bytes.
Value Offset
This tag records the offset from the start of the TIFF header to the position where the value itself is recorded. In
cases where the value fits in 4 bytes, the value itself is recorded. If the value is smaller than 4 bytes, the value is
stored in the 4-byte area starting from the left, i.e., from the lower end of the byte offset area. For example, in big
endian format, if the type is SHORT and the value is 1, it is recorded as 00010000.H.
Note that field Interoperability shall be recorded in sequence starting from the smallest tag number. There is no
stipulation regarding the order or position of tag value (Value) recording.