Specifications

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The alpha expansion, shown in Figure 4-18, is performed by referencing the
hardwired-expansion-table. The table contents are listed in Table 4-8. For an
example, When A_INDEX is 3 then result α is 4-bit 0110, i.e., 6 in integer and 0.4
(= 6/15) in fixed-point.
C_INDEX[2:0]
Result α[3:0]
0 0
1 2
2 4
3 6
4 8
5 10
6 12
7 15
Table Table 4-6. Alpha Expansion Table
4.13.1.2. 4444-αRGB Format
For 4444-αRGB format, R, G and B component of each pixel are constructed by bit
expansion logic operation as shown in Figure 4-19 (α is from input pixel data
without bit expansion):
α[3:0] = bit[15:12],
R[5:0] = {bit[11:8], bit[11:10]}
G[5:0] = {bit[7:4], bit[7:6]}
B[5:0] = {bit[3:0], bit[3:2]}
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
b[3:0] b[1:0] b[7:4] b[7:6] b[11:8] b[11:10]
α[3:0]
4- bit to 6 - bit
expansion
4- bit to 6 - bit
expansion
4- bit to 6 - bit
expansion
4444- αRGB color
R[3:0]
G[3:0]
B[3:0]
α[3:0]
R[5:0] G[5:0] B[5:0]
Figure 4-17. The Bit Expansion for 444-αRGB Color