Analog Gain And Black Level; Analog Gain - Smartek UCC User Manual

User Manual - twentynine

5.2.2 Analog Gain and Black Level

After the charge was read out from the active pixel array it needs to be amplified according to the input levels
of the analog-to-digital converter, or even higher to lighten up dark scenes without raising the exposure time
or adding light.

5.2.2.1 Analog Gain

Figure 33 illustrates a typical image acquisition signal chain in SMARTEK Vision digital cameras.
The analog voltage generated by the sensor will be passed through the Variable Gain Control where it is
amplified by a factor, configurable by the camera's Gain value.
BlackLevel
OBC
Gain
U
obc
U U
in amp
+
Sensor VGC ADC
FPGA
Figure 33: Typical signal chain in a CCD/CMOS image sensor
In SMARTEK Vision digital cameras gain values are expressed in decibels (dB), the analog gain defines the
ratio between the output and input voltage value in a base 10 logarithmic scale:
U
amp
Gain = 20 × log
dB 10
U
in
For calculating the linear amplification factor from the gain value in dB, the reverse function can be applied:
Gain dB
U
amp
= 10
20
U
in
Gain modification is also useful for enhancing the image brightness, especially in low light condition.
Increasing a gain value means increasing the intensity of each pixel, resulting in a brighter image. However,
the image noise will also increase when gains are increasing. Figure 34 shows two images with different
gain settings. The image on the right is captured with a gain value of 19 dB, while the image on the left is
captured with a gain value of 14 dB. Like expected the right image appears brighter than the left one.
47
SMARTEK Vision | User Manual - twentynine | Doc. v1.0.2