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Genie Monochrome Series-GigE Vision Camera Operational Reference

37
Gain and Black Level Controls
The Genie series of monochrome cameras provide gain and black level adjustments for the analog signal from each
CCD pixel, before the analog to digital conversion. The software gain and black level controls can make small
compensations to the acquisition in situations where lighting varies and the lens iris can not be easily adjusted. The
user can evaluate Gain and Black Level by using CamExpert.
Features and limitations are described below.

Gain is expressed in decibels (dB). Range from -6dB to +12dB in 0.1dB increments. Gain is a multiplication
factor to the analog signal (i.e. exposure) before digitization.
Note that a gain of 6dB is a multiplier of 2 (doubles the level).

Increasing gain increases the amplitude of the analog video signal but also increases the sensor analog noise
proportionately, before analog to digital conversion.

Note: Doubling gain does not necessarily double the digital data due to the Black Level Offset value as
described below.

Black level offset is applied to the sensor analog signal to shift the DC level of the video signal. Black level is
an additive offset to the analog video signal before digitization.

Black level offset increases the brightness of the video signal equally. Therefore any area of the video that is
black will brighten to some gray level as offset is increased.

Black level offset is expressed as a number ranging from -128 to 127. The offset is achieved as a change in the
analog signal from the sensor where (in 8-bit mode) a control number change of 1 is 1/16
th
of a DN (digital
number) pixel change. In other words, a control change of 16 is required for each change in pixel value,
therefore a maximum control value of 127 will cause a black pixel (00) to have a gray value of about 8. In 10-
bit mode, black level offset is 1/4 DN.

The resultant output Gain/Offset formula is
 
Offset Gain Exposure OutputData
 
*
Gain and Offset Control via Sapera LT or GigE Vision Compliant
Applications
Sapera
Genie Sapera parameters for Gain and Black level:
Gain = Amplification in dB from -6.0 to 12.0 dB
BlackLevel = DC offset in 1/16 of DN in 8-bit mode or 1/4 DN in 10-bit mode;
range from -128 to 127
In CamExpert, these parameters are available under the “Sensor” tab.
See
" Accessing Features with + LT " on page 74 .
XML features for Gain and Black level:
GainRaw = Analog gain in tenth of dB (0.1 dB)
BlackLevelRaw = Black level (offset) in 1/16 of DN in 8-bit mode or 1/4 DN in 10-bit mode