Color/Grayscale Dithering
11-15
LCD Controller
11.5 Color/Grayscale Dithering
Entries selected from the lookup palette are sent to the color/grayscale space/
timebase dither generator. Each 4-bit value is used to select one of 15 intensity
levels. Two of the 16 dither values are identical (most intense). The gray/color
intensity is controlled by turning individual pixels on and off at varying periodic
rates. More intense grays/colors are produced by making the average time
that the pixel is off longer than the average time that it is on. The dither genera-
tor also uses the intensity of adjacent pixels in its calculations to give the
screen image a smooth appearance. The proprietary dither algorithm is opti-
mized to provide a range of intensity values that match the visual perception
of color/gray gradations. In color mode, three separate dither blocks are used
to process the three color components: red, green, and blue.
The duty cycle and resultant intensity level for all 15 color/grayscale levels is
summarized in Table 11–3.
Table 11–3.
Color/Grayscale Intensities and Modulation Rates
Dither Value
(4-Bit Value From Palette)
Intensity
(0% is White)
Modulation Rate
(Ratio of ON to ON+OFF Pixels)
0000
0.0%
0
0001
11.1%
1/9
0010
20.0%
1/5
0011
26.7%
4/15
0100
33.3%
3/9
0101
40.0%
2/5
0110
44.4%
4/9
0111
50.0%
1/2
1000
55.6%
5/9
1001
60.0%
3/5
1010
66.6%
6/9
1011
73.3%
11/15
1100
80.0%
4/5
1101
88.9%
8/9
1110
100.0%
1
1111
100.0%
1