M10510B;17/58
- 17 -
(5-3) Level setting
The level setting is mostly divided into the
following two groups:
●
Gain setting
This is to set the gain (amplification factor)
of the preamplifier between the CCD image
sensor inside the camera and A/D converter.
●
Offset setting
This is to set the offset value of the
preamplifier between the CCD image sensor
inside the camera and A/D converter.
→
Refer to the next section (Section 6) for
the specific setting method.
(Note) As for the offset setting, it is
recommended to use the factory
default value except for a special case.
(Note) Follow the procedure (gain setting
followed by offset setting) if fine tuning
of the offset value is needed.
(5-4) Gain setting of preamplifier
●
Gain variable amplifier and integrated gain
The image signal output from CCD is amplified inside the
camera through the fixed gain amplifier on the anterior
stage and then through the following variable gain amplifier
before being input into the A/D converter.
The left block chart shows this flow.
(Note) The gain value (dB) described here is the one based on
the CCD output (0 dB) as the baseline.
●
Correlation between MGC gain setting value and MGC gain
The MGC setting value of this equipment is controlled
by giving 0 to 255.
The correlation between this setting value and the
MGC gain (integrated gain including the gain of the
variable gain amplifier and that of the fixed gain
amplifier) is shown in the right graph.
(Note) When the CCD element receives excessive light
with a low gain value of the amplifier due to the
restriction of the dynamic range of the CCD light
receiving element, the signals of the nonlinear
area of the CCD element and the preamplifier
are output at the high brightness area.
In this state, unnatural image (Note below) may
appear in the neighborhood of the saturating
signal area of the image due to the
characteristic of the nonlinear area. This
phenomenon, which is associated with the
saturation characteristic of the CCD element, is
not a failure arising from the camera.
To eliminate this phenomenon, reduce the
amount of light by stopping down the lens and
newly set a higher gain value. Then, the output
signal from the CCD element at the saturating
area will be appropriately saturated into a white
level for the output.
Signal level
Time
Time
Time
１０ ２ ３
０
０
１ ０ ２３
０
Increase in OFFSET
Increase in GAIN
Image signal
１ ０２ ３
(Befor setting
adjustment
)
Conceptual diagram of gain and offset levels
Signal level
Signal level
CCD
Preamplifier
A/D
GAIN
Variable gain amplifier
5.1dB
～
32.6dB
Integrated gain
MGC setting
Fixed gain amplifier
6dB Fixed
11.1dB
～
38.6dB
42
36
30
24
18
12
6
0
64
128
192
(255)
MGC GAIN CODE
M
G
C
G
A
IN
(d
B
)