Digital Signal Processing Reference
In-Depth Information
Example baseline tables are provided in the JPEG standard, as
shown in the Table 13.1 below:
Luminance Quantization Table
16
11
10
16
24
40
51
61
12
12
14
19
26
58
60
55
14
13
16
24
40
57
69
56
14
17
22
29
51
87
80
62
18
22
37
56
68
109
103
77
24
35
55
64
81
104
113
92
49
64
78
87
103
121
120
101
72
92
95
98
112
100
103
99
Chrominance Quantization Table
17
18
24
47
99
99
99
99
18
21
26
66
99
99
99
99
24
26
56
99
99
99
99
99
47
66
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
Many other quantization tables claiming greater optimization
for the human visual range have been developed for various JPEG
versions.
The quantized output array B is formed as follows:
B
j,k
¼
{0.7}
where A
j,k
is the DCT output array value, Q
j,k
is the quantiza-
tion table value.
Examples would be:
Luminance DCT output value of (A
0,0
)
rounded (A
j,k
/Q
j,k
) for j
{0.7}, k
¼
¼
426.27
¼
B
0,0
¼
round (A
0,0
/Q
0,0
)
round (426.27 / 16)
27
¼
¼
Chrominance DCT output value of (A
6,2
)
40.10
¼
0
Few values of the output B
j,k
are possible when the quanti-
zation value is high. Using a quantization value of 99, the rounded
output values can only be
B
6,2
¼
round (A
6,2
/Q
6,2
)
round (
40.10 / 99)
¼
¼
1. In many cases, especially
when j or k is three or larger, the B
j,k
will be rounded to zero,
indicating little high-frequency in the image region.
This is lossy compression, so called because data is lost in
quantization, and cannot be recovered. The principle is to
1, 0 or
þ
