JEITA CP-3451
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4.7.2 Interoperability Structure of APP1 in Compressed Data
APP1 consists of an APP1 marker indicating that it is an application area, a length code indicating its size, and
primary image attribute information patterned after the TIFF structure. The APP1 segment cannot record more than
64 Kbytes, a limitation that shall be kept in mind when recording thumbnail images.
APP1 also records attribute information for JPEG compressed images. The features of this marker segment are
described below.
A. Order of APP1 recording
APP1 is recorded immediately after the SOI marker indicating the start of the file (see Figure 6).
B. APP1 Interoperability structure
APP1 consists of an APP1 marker, Exif ID code and the attribute information itself (see Figure 25).
Address Offset
Code
Meaning
(Hex)
(Hex)
+00
FF
Marker Prefix
+01
E1
APP1
+02
Length of field
+04
45
'E'
+05
78
'x'
+06
69
'i'
+07
66
'f'
+08
00
NULL
+09
00
Padding
+0A
Attribute information
Figure 25 Basic Structure of APP1 Marker Segment
C. Exif ID code
The Exif ID code indicates that the APP1 segment Interoperability is Exif format. After a 4-byte code, 00.H is
recorded in 2 bytes. The reason for recording this code is to avoid duplication with other applications making use of
JPEG application marker segments (APPn).
D. Attribute information
Attribute information is recorded in 2 IFDs (0th IFD, 1st IFD) following the TIFF structure, including the File Header.
The 0th IFD records compressed image attributes (the image itself). The 1st IFD may be used for thumbnail
images.
E. TIFF header
The TIFF header in APP1 constitutes 8 bytes of data, including the byte order and the Offset of IFD indicating the
first IFD. The Offset is referenced to the address of the first byte of the Byte Order. For example, the Offset of IFD
address in the TIFF Header is 4 (see Table 1).
F. Relation to JPEG marker segments
Attribute information is recorded in essentially the same format as that used to record uncompressed data attribute
information. In order to avoid duplication, however, attribute information recorded in a JPEG marker segment is not
recorded in APP1.