JEITA CP-3451
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4.7 JPEG Marker Segments Used in Exif
In addition to the compressed data (Interoperability coded data), a compressed file contains one each of the marker
segments APP1, DQT, DHT, SOF and SOS. The compressed data begins with an SOI and ends with an EOI
marker. A restart marker (DRI, RSTm) may be inserted optionally. Another option is to have two or more APP2
marker segments. APPn other than APP1 and APP2 or COM segments are not used by Exif. However Exif readers
should be designed skip over unknown APPn and COM.
APP1 shall be recorded immediately after SOI, and if there is an APP2 it follows after APP1. DQT, DHT, DRI and
SOF come after APP2 and before SOS, in any order.
The marker segments used in Exif are listed in Table 18.
Table 18 Marker Segments
Marker Name
Marker Code
Description
SOI
Start of Image
FFD8.H
Start of compressed data
APP1
Application Segment 1
FFE1.H
Exif attribute information
APP2
Application Segment 2
FFE2.H
Exif extended data
DQT
Define Quantization Table
FFDB.H
Quantization table definition
DHT
Define Huffman Table
FFC4.H
Huffman table definition
DRI
Define Restart Interoperability
FFDD.H
Restart Interoperability definition
SOF
Start of Frame
FFC0.H
Parameter data relating to frame
SOS
Start of Scan
FFDA.H
Parameters relating to components
EOI
End of Image
FFD9.H
End of compressed data
The data structures of markers defined in JPEG Baseline DCT and used in Exif compressed files, as well as the
APP1 and APP2 data structures defined specifically for this standard, are explained below.
4.7.1 JPEG Marker Segments
The data structure of JPEG marker segments other than APP1 and APP2 is noted below.
A. Start of compressed data (SOI: Start of Image)
SOI is a marker code indicating the start of compressed data (see Figure 18).
Address Offset
Code
Meaning
(Hex)
(Hex)
+00
FF
Marker Prefix
+01
D8
SOI
Figure 18 SOI Structure