background image
ISO/IEC 10918-1 : 1993(E)
Pq:
Quantization table element precision Specifies the precision of the Q
k
values. Value 0 indicates 8-bit Q
k
values; value 1 indicates 16-bit Q
k
values. Pq shall be zero for 8 bit sample precision P (see B.2.2).
Tq:
Quantization table destination identifier Specifies one of four possible destinations at the decoder into
which the quantization table shall be installed.
Q
k
:
Quantization table element Specifies the kth element out of 64 elements, where k is the index in the zig-
zag ordering of the DCT coefficients. The quantization elements shall be specified in zig-zag scan order.
Table B.4 Quantization table-specification parameter sizes and values
Values
Parameter
Size (bits)
Sequential DCT
Progressive DCT
Lossless
Baseline
Extended
Lq
16
16
2
65
64
1
+
+
=
t
n
Pq t
( )
>
C
Undefined
Pq
1
4
16
0
0, 1
0, 1
Undefined
Tq
1
4
16
0-3
Undefined
Q
k
1
8, 16
1-255, 1-65 535
Undefined
The value n in Table B.4 is the number of quantization tables specified in the DQT marker segment.
Once a quantization table has been defined for a particular destination, it replaces the previous tables stored in that
destination and shall be used, when referenced, in the remaining scans of the current image and in subsequent images
represented in the abbreviated format for compressed image data. If a table has never been defined for a particular
destination, then when this destination is specified in a frame header, the results are unpredictable.
An 8-bit DCT-based process shall not use a 16-bit precision quantization table.
B.2.4.2
Huffman table-specification syntax
Figure B.7 specifies the marker segment which defines one or more Huffman table specifications.
TISO0890-93/d025
DHT
Lh
Tc Th
L
1
L
2
L
16
Define Huffman table segment
Symbol-length
assignment
Multiple (t = 1, ..., n)
Symbol-length assignment parameters
Figure B.7 Huffman table syntax
V
1,1
V
1,2
V
1,L
1
V
2,1
V
2,2
V
2,L
2
V
16,1
V
16,2
V
16,L
16
Figure B.7 [D25], = 5.5 cm = 215.%
40
CCITT Rec. T.81 (1992 E)
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