AN2621 Freescale Semiconductor / Motorola, AN2621 Datasheet - Page 6

• Manufacturer Part Number: AN2621
• Description: MPC8220i PF300 Image Coprocessor Operation
• Manufacturer: Freescale Semiconductor / Motorola

Color Conversion Unit (CCU)
Table 1 shows the contents of typical index and remainder tables for one of the three input dimensions. In
this example, the table has 12 indices, or table entries (N
is programmable within the range of 2 to 256. The first table entry spans three input addresses, so the
remainder table for addresses in this span are programmed with 255–0×(255/3), 255–1×(255/3), and
255–2×(255/3). The second table entry spans nine input addresses, so the remainders table is programmed
with 255–0×(255/9), 255–1×(255/9), 255–2×(255/9), 255–3×(255/9), … 255–7×(255/9), and
255–8×(255/9). The index and remainder table entries for the rest of the addresses are programmed in a
similar manner. Each of the three input channels has its own set of index and remainder tables, so there is
no requirement for the color table to be indexed the same way in each dimension.
The three-dimensional color lookup table itself is programmed with the desired output values for the input
addresses that constitute the first of each span (that is, those with zero remainders, 255 as programmed
values). They are aligned with the indices.
In use, a triplet of 8-bit color values for each pixel is input to the block. Each individual 8-bit color value is
used to address its separate index and remainder tables. This results in the coordinates of a
three-dimensional color lookup table grid point (the three indices) and a three-dimension vector
representing the fractional distance to the next table grid point in each dimension (the reminders). Since the
three indices cannot be interpreted directly as an address to the color lookup table memory, they must first
be combined to form the addresses of the eight color lookup table grids that surround the point being
interpolated. This is accomplished by using the indices to address the CCU offset lookup table memory and
summing the result to form a physical address of the location in system memory containing the output color
data for the required grid point. The CCU offset lookup table must be programmed with the proper decoding
algorithm according to the following equations:
In each of these equations, the BaseAdr is the starting address of the sparse color lookup table in system
memory. I is the index number for the table. N
6
Address
245
246
247
248
249
250
251
252
253
254
255
Table 1. Example of CCU Index and Remainder Tables for Linear Interpolation (continued)
Input color channel 1: Offset Value = BaseAdr + (I–1) × 4
Input color channel 2: Offset Value = N
Input color channel 3: Offset Value = N
Index Table
Contents
10
10
10
10
10
10
12
11
11
11
11
Remainder
116
139
162
185
209
232
128
191
MPC8220i PF300 Image Coprocessor Operation
Freescale Semiconductor, Inc.
64
0
0
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Remainder
Contents
Table
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139
116
255
191
128
255
93
70
46
23
64
1
1
1
and N
End of range of addresses of tenth table entry
Start of range of addresses of eleventh table entry
End of range of addresses of eleventh table entry
Last table entry
× (I–1) × 4
× N
2
2
* (I–1) × 4
are the number of table indices in each of the first
i
= 12, for this dimension). The number of indices
Comments
MOTOROLA