The data associated with an annotation tag in a TIFF file consists of zero or more blocks of default data, followed by the data necessary to describe each annotation mark. Default data consists of default named blocks, designated Type 2 data. Annotation mark data consists of an attribute structure, designated Type 5 data, followed by one or more named blocks, designated Type 6 data.
The annotation data itself consists of a 4-byte header, which is not currently used (reserved for future use). The header should be skipped on read and written as zeros. Note, however, that it is included in the TIFF tag's Data Count field. The header is followed by four bytes in Intel order that specify size of INTs and UINTs and byte ordering:
| 4 bytes | 0 = Intel 16 bit | (least significant byte to most significant byte and two byte INTs and UINTs) |
| 1 = Intel 32 bit | (least significant byte to most significant byte and four byte INTs and UINTs) |
Default data and mark data follow:
4 bytes = type of data (integer 2, 5, or 6, as explained below)
4 bytes = size of data (not including named block data)
Variable data follows, depending on the data type.