8 Introduction to the Two Point Correction (A, B, E, J, K, N)
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Introduction to the Two Point Correction (
A
,
B
,
E
,
J
,
K
,
N
)
The two point correction is the most elaborate correction module of the IRC-320 camera models. For
this reason initially a general survey of the two point correction functioning shall be given. This
information in connection with the indications of the following section
will probably be sufficient for most users, due to the fact that the determining and
adjustment of nearly all parameters is already executed ex factory and normally, no user intervention
is necessary at all. In case that nevertheless a more extensive understanding of the current parameters
should be required, chapter 10
Advanced Parameters and Commands
By means of the two point correction (also called “Gain Offset Correction”) usually, the distinctive
underground structure of the microbolometer sensor can be equalized. The target is to transmit the
individual characteristic curve of each pixel to a set characteristic curve, being valid for all pixels. In
order to achieve this result, initially the effective characteristic curve of each single pixel is determined
by taking up data samples. A linear characteristic curve is supposed so that two data samples are
sufficient for a definite determination. By means of recording two reference images at the scene
temperatures T
A
und T
B
the data samples can be determined for all pixels. Furthermore the digital set
values J and K each belonging to the temperatures T
A
and T
B
are determined.
Owing to the four parameters mentioned above, the two point correction is now able to modify the
gain and the offset of each pixel characteristic curve in a way that it is congruent with the set
characteristic curve. Therefore, in an optimum case, an image structure, caused by the sensor, does no
longer occur. The below mentioned sketch tries to exemplary explain the facts on the basis of one
single pixel characteristic curve:
Counts
Set Characteristic
Curve
The reference images are stored in several files within the flash and are directly transferred into the
correction memory following the camera start-up. The parameter
A
indicates the file number of the
correction image at low reference temperature T
A
. The parameter
B
serves the same purpose for the
reference image at temperature T
B
.
For improvement of image quality the camera usually is delivered ex-factory with several sets of
correction data, which are determined for diverse operating conditions. I.e. diverse correction images
(
A
,
B
) including the according set values (
J
,
K
) may exist for the two point correction, being loaded
during the camera start-up to the correction memory.
T
A
T
B
J
K
Effective
Characteristic
Curve
Temperature [°C]
B
A
Cold Reference pixel )
Warm Reference pixel )
VDS Vosskühler GmbH
IRC-320
