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Chapter 8 Readout 57
8.1.2.2 Exposure Time is Shorter than Readout Time
Figure 8-5 illustrates the timing diagram for Expose During Readout when Exposure
Time is shorter than Readout Time.
Figure 8-5: Timing Diagram: Frame Transfer Readout, t
exp
< t
ro
However, there are a number of caveats associated with this timing situation, primarily
a risk of overexposure. This is due to the fact that the sensor is collecting signal while
readout is occurring, which is illustrated by the Wait Time periods in
Figure 8-5 .
Overexposure can be avoided by turning the light source off (or blocking it) during the
wait time. One way to do this is to control the light source via TTL with the Exposing
Output Signal.
NOTE:
The first frame in Figure 8-5 is never overexposed.
For this application, regardless of when a frame’s exposure starts or ends, the reading
out of data cannot begin until the prior frame’s data have been completely read out.
Therefore, the effective Exposure Time is actually equal to the Readout Time.
Consequently, the Frame Rate for these scenarios is defined by the Readout Time.
44
11
-0
16
9
_
0
0
54
F
RAME
1
2
3
F
RAME
F
RAME
E
XP
OSE
R
EADOUT
E
XP
OSE
R
EADOUT
E
XP
OSE
R
EADOUT
W
AIT
T
IME
W
AIT
T
IME