Figure 7-3. graphics matrix for 50% duty cycle -20 – Cirrus Logic EP93xx User Manual
Page 202
7-20
DS785UM1
Copyright 2007 Cirrus Logic
Raster Engine With Analog/LCD Integrated Timing and Interface
EP93xx User’s Guide
7
7
7
The values in between full on and full off are more difficult to determine and depend on the
display characteristics such as persistence, turn on time, and refresh rate. To achieve
difference in shades of gray, it is typical to have more values below the half luminance
average due to the higher sensitivity to luminance variations by the human eye at lower
levels. Other problems that occur with choosing patterns and the operating matrix parameters
are flickering (temporal distortion), walking patterns (spatial distortion), and spatial
interference patterns.
Take, for example, a 50% duty cycle. We could define the matrix as a 4Hx4Vx4F as shown in
. However, we effectively halved the refresh rate of these pixels and, depending on
the refresh rate of the display, are likely to see flickering for this shade.
Figure 7-3. Graphics Matrix for 50% Duty Cycle
To avoid flickering, it is better to play a spatial trick and turn on every other pixel so that the
eye integrates the on and off pixels between two consecutive frames. However, in the case
given in
, a spatial interference can be caused if an image displayed in this
grayscale consists of every other column activated. For this case, we would be right back to
the flickering problem shown in
. This would be true if we switched to a checker
board pattern and displayed a checker board image or almost any other pattern.
Frame 0
H O R Z
Frame 1
V
1
1
1
1
0
0
0
0
E
1
1
1
1
0
0
0
0
R
1
1
1
1
0
0
0
0
T
1
1
1
1
0
0
0
0
Frame 2
Frame 3
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0