STV0974E datasheet(17/69 Pages) STMICROELECTRONICS

17 / 69 page

Functional description

STV0974

17/61

4.4.4

Quantization block

This block applies a uniform quantizer on all DCT coefficients, in ZigZag sequence. It is compliant

with ISO DIS 10918-1 Annex A - Section A.3.4.

The quantizer step size for each DCT coefficient Suv is the value of the corresponding element Q’uv

from the quantization table Q’.

Where

uv is the index of the zigzag coefficient.

Table Q’ is a scaled quantization table calculated for table Q as follows:

where

Squeeze is a parameter value.

Table Q is represented in

Figure 9, as described in ISO DIS 10918-1 Annex K.

Table 6 shows an example of VGA image when different squeeze values are applied by the user.

Figure 9: Luminance and chrominance quantization tables

Quantization table for Y blocks

Quantization table for U and V blocks

Table 6: VGA image size - YUV 4: 2: 2 - Example of image size after JPEG compression

Squeeze

a. No compression

102030

Squeeze

quantization table

factor (Squeeze/8)

0.12

0.25

0.5

0.62

1.25

1.87

3.12

4.19

File size (Kbyte)

614

~80

~51

~32

~27

~21

~12

Bit per pixel

2.13

1.39

0.85

0.72

0.56

0.32

0.24

Squv

round

Suv

Q'uv

------------

⎝⎠

⎛⎞

Squeeze

-------------------------

16 11 10 16 24

12 12 14 19 26

14 13 16 24 40

14 17 22 29 51

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

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

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