background image
ISO/IEC 10918-1 : 1993(E)
B.1.4
Conventions for symbols, code lengths, and values
Following each syntax figure in B.2 and B.3, the symbol, name, and definition for each marker and parameter shown in
the figure are specified. For each parameter, the length and allowed values are also specified in tabular form.
The following conventions apply to symbols for markers and parameters:
all marker symbols have three upper-case letters, and some also have a subscript. Examples: SOI, SOF
n
;
all parameter symbols have one upper-case letter; some also have one lower-case letter and some have
subscripts. Examples: Y, Nf, H
i
, Tq
i
.
B.2
General sequential and progressive syntax
This clause specifies the interchange format syntax which applies to all coding processes for sequential DCT-based,
progressive DCT-based, and lossless modes of operation.
B.2.1
High-level syntax
Figure B.2 specifies the order of the high-level constituent parts of the interchange format for all non-hierarchical
encoding processes specified in this Specification.
TISO0840-93/d020
Compressed image data
SOI
Frame
EOI
Tables/
misc.
[
[
Frame header
DNL
segment
Scan
2
[
[
[
[
Scan
1
[
[Scan
last
Tables/
misc.
[
[
Scan header
[ECS
0
Scan
Frame
ECS
last-1
ECS
last
RST
last-1
]
Entropy-coded segment
0
Entropy-coded segment
last
<MCU >, <MCU >, <MCU >
1
2
Ri
<MCU >, <MCU >, <MCU >
n
n + 1
last
Figure B.2 Syntax for sequential DCT-based, progressive DCT-based,
and lossless modes of operation
RST
0
Figure B.2 [D20], = 10 cm = 391.%
The three markers shown in Figure B.2 are defined as follows:
SOI:
Start of image marker Marks the start of a compressed image represented in the interchange format or
abbreviated format.
EOI:
End of image marker Marks the end of a compressed image represented in the interchange format or
abbreviated format.
RST
m
:
Restart marker A conditional marker which is placed between entropy-coded segments only if restart
is enabled. There are 8 unique restart markers (m = 0 - 7) which repeat in sequence from 0 to 7, starting with
zero for each scan, to provide a modulo 8 restart interval count.
The top level of Figure B.2 specifies that the non-hierarchical interchange format shall begin with an SOI marker, shall
contain one frame, and shall end with an EOI marker.
34
CCITT Rec. T.81 (1992 E)
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