Smartek Vision Giganetix GC Series User Manual page 118

Function
bool GetFloatNodeValue(
"Gain", double &nodeValue) const
bool SetFloatNodeValue(
"Gain", double nodeValue)
bool GetFloatNodeMin(
"Gain", double &nodeMinValue) const
bool GetFloatNodeMax(
"Gain", double &nodeMaxValue) const
Black Level
As shown in Figure 92 as well, the analog-to-digital conversion circuit includes beside the ADC an additional
component with the target to remove dark current noise from the signal of each pixel. Dark current is a
charge of each pixel which is generated continuously by thermal energy within the silicon lattice, even when
no light enters the sensor. As its charge in the photosensitive pixels is not connected to the amount of light
entering, it is no useful signal and needs to be removed before digitizing the signal, as it negatively effects
the signal to noise ratio.
To help to remove the dark current noise, image sensors usually provide an array of optically shielded pixels
(lines and columns, covered by a non-transmissive metal coating). Due to the coating they are at no time
exposed to light and are taken as reference value for the dark current. The Optical Black Clamping (OBC)
circuit, shown in Figure 92, ascertains the average digital value of the dark pixels and subtracts it from an
offset, named as clamp level. The overall value (usually negative) is then added to the amplified signal:
The clamp level can be accessed by the BlackLevel property of the camera. It provides percentage access
to the value range of the clamp level register of the analog frontend (CCD) or the sensor (CMOS) and is by
default set to 0. It can be used to reduce the amount of Dark Noise subtracted from the signal or to add a
user defined offset to the signal. The available clamp level ranges are shown in Table 48.
Camera Type
All Models (CCD Sensors)
All Models (CMOS Sensors)
Table 48: Range Overview of Clamp Level for CCD and CMOS Cameras
SMARTEK Vision digital cameras based on CCD technology can only apply Analog
Gain and BlackLevel values to all channels (per tap) at one time.
Note
gain settings (digital) can be achieved by software using the ImageProcAPI in the
GigEVisionSDK.
Table 47: Gain - Access through API
U = U + ClampLevel −
amp
obc
Clamp Level (in DN)
0 to 1023
-255 to 256
112
Description
Get value of IFloat node Gain.
Set value of IFloat node Gain.
Get minimum value of IFloat node Gain.
Get maximum value of IFloat node Gain.
n
(U )
dark i
i=0
n
BlackLevel (in % of Clamp Level)
SMARTEK Vision Giganetix User Manual Version 2.1.4
4 Image Acquisition
0 to 100
0 to 100
Individual