FLIR X-Series User Manual page 60

x
Detector
Analog
Gain/Offset
The analog FPA data is passed through an analog gain and offset stage that are factory-set to ensure
that the entire range of the FPA output is matched to the A/D input. This is shown in the figure below,
which plots the digital output of a typical camera against background photon flux. The actual scale of
the flux depends on integration time setting. The figure shows an example where the user desires to
operate the camera between two flux points such that these two limits use the entire 14 bit range.
With no global gain and offset adjustment these two points correspond to 3200 counts and 15800
counts for the low and high flux ranges respectively. Having obtained these numbers, we set the gain
to use the full 14-bit range:
Since the offset stage is after the gain stage, we calculate the offset value using the gain:
These values are then entered into the global gain and offset controls and the linearized (red curve)
transfer function shown is the result.
The available gain range is 1.999 to essentially zero; the available offset range is + 32767. The
default values are a gain of 1 and an offset of zero. Because the system sensitivity (NET) is set prior
to the A/D stages, there is no detrimental effect on performance from the use of the global gain and
offset controls.
18000
As linearized
16000
14000
Typical camera
setup, gain = 1 12000
offset = 0
10000
X-series User's Manual
+
14-bit A/D
X-series Signal Processing Chain
gain
=
offset
18000
16000
14000
12000
10000
8000
8000
6000
6000
4000
4000
desired operating range
2000
2000
0
0
Background flux
Use of global gain and offset to linearize the camera
Bad Pixel
x +
Replacement
Algorithm
NUC Table
16383
= =
. 1 30
−
15800 3200
−  = −
3200 gain 4160
5 – X-series Camera Controller
x +
Uncorrected Data
x +
Corrected Data
Digital
Gain/Offset
60