參數(shù)資料
型號(hào)： μSAP70300-B03
廠商： NEC Corp.
元件分類： 8位微控制器
英文描述： 8 Bit Single Chip Microcontrollers
中文描述： 8位單片機(jī)微控制器
文件頁數(shù)： 38/102頁
文件大?。?/td> 282K
代理商： ΜSAP70300-B03
28
μ
SAP703000-B03 USER'S MANUAL
(4) Reverse quantization
Reverse quantization involves multiplying the 8 x 8 pixel matrix obtained as a result of Huffman decoding,
by a quantized matrix defined by the quantization segment.
Because this processing only involves calculating the product of the two values read from memory,
followed by writing the result to another memory address, processing that restores the original sequence
of a zigzag scan is also performed at the same time, so that the number of times memory is accessed
can be reduced and the overall processing speed improved.
Almost all the elements of the matrix obtained as a result of Huffman decoding have a value of ‘0’ (zero).
The normal CPU requires several clocks to execute the multiplication or memory access (read or write).
The AP703000-B03 inserts one expression to identify whether the value of an element is ‘0.’ If the value
is ‘0,’ that element is rejected.
(5) Actuality of DCT/reverse DCT
DCT is equivalent to repeating the following one-dimensional calculation twice (vertically and horizontally).
F(u,v ) = 2C(u )C(v )/N*
ΣΣ
f (i j )*cos {(2i + 1)u
π
/2N} *cos {(2j + 1)v
π
/2N}
= 2C(u )C(v )/N*
Σ
cos {(2i + 1)u
π
/2N} *
Σ
f (i j )*cos {(2j + 1)v
π
/2N}
The number of constants required for two dimensions and eight orders (N = 8; i.e., 8 x 8 matrix) is 32.
Actually, however, this can be decreased by applying the formulae of a trigonometric function to the
subsequent seven.
cos(n
π
/16) (n = 0, 1, 2, ... 31)
↓
cos (n
π
/16) (n = 1, 2, 3, 4, 5, 6, 7)
If the following value has been calculated in advance, the number of times multiplication is executed can
be reduced.
f (0, j )
±
f (7, j ), f (1, j )
±
f (6, j ), ...
Further, the vertical and horizontal routines can be used commonly if the DCT expression is changed as
follows:
g (i v ) =
Σ
f (i, j )*cos {(2j + 1)v
π
/16}
f (u, v ) =
Σ
g (i, v )*cos {(2i + 1)u
π
/16}
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