MB87P2020 Datasheet, PDF (113/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

AAF Antialiasing Filter
Formulas for sequential averaging of foreground and background data are shown in table 1-1. Pixel data
from PP is fg, background from memory is bg and fg’ is the new resulting pixel, which is written to video
memory. The low precision of the 2x2 super sampling can be compensated by adaptive coefficient selec-
tion, controlled by color difference thresholds. The value of the thresholds depends on human eye sensitiv-
Table 1-1: Formulas for sequential averaging
Formula
fg’ = (2 fg + 2 bg) / 4
fg’ = (1.5 fg + 3 bg) / 4
fg’ = (1.5 fg + 15 bg) / 16
Condition
2x2 super sampling size. If difference between fg and bg color is below
threshold. Threshold1 applies if fg<bg, otherwise threshold2.
2x2 super sampling size. If difference between fg and bg color is
greater or equal threshold. Threshold1 applies if fg<bg, otherwise
threshold2.
4x4 super sampling size. No threshold based coefficient adaption
required.
ity on chrominance contrast and differs for various types of graphics. Right setup values could be evaluated
empirically.
Addresses of pixel coordinates are divided by 2 in 2x2 super sampling mode for each X/Y dimension. In
4x4 super sampling mode pixel address of resulting pixel is divided by 4. Thus 4 or 16 sub-pixels of the
generated high-resolution object are mapped to the same pixel address in video memory. The sequential av-
eraging is the result of the multiple applied formula on the same memory address.
1.2 Configuration Registers
The following table shows the configuration registers of AAF and their initial values.
Table 1-2: AAF related Registers
Address
Name
4124h PPCMD_EN
4500h
AATR_TH2
AATR_TH1
4504h
AATG_TH2
AATG_TH1
4508h
AATB_TH2
AATB_TH1
450Ch
AAOE_WBO
AAOE_BX4
Width
Comment
1 bit[16] - AAF_EN: enable anti aliasing filter
(high active)
16 bit[15:8] - threshold2
bit[7:0] -threshold1
for colour channel red
16 bit[15:8] - threshold2
bit[7:0] - threshold1
for colour channel green
16 bit[15:8] - threshold2
bit[7:0] - threshold1
for colour channel blue
1 bit[0] - OPTI_EN: write back optimization
bit[1] - Operator size (0=2x2, 1=4x4)
Init. Value
0h
0h
FFh
0h
FFh
0h
FFh
0h
Note!
The number of the used bits of threshold registers depends on colour depth. That meens:
• RGB888: for all colour channels all bits of threshold registers are used by AAF algorithm
• RGB565: for the red and blue colour channel only the bit[7:3] are used for calculation and for the
green channel the bit[7:2]
Functional Description
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