FLIR X6520sc Series, User Manual

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Radiometric measurement 8
8.1 Non-uniformity correction (NUC)
8.1.1 General
NUC refers to the process by which the camera electronics correct for the differences in
the pixel-to-pixel response of each individual pixel in the detector array. The camera can
create (or allow for the user to load) a NUC table that consists of a unique gain and offset
coefficients and a bad pixel indicator for each pixel. The table is then applied in the digital
processing pipeline as shown in Figure 8.1. The result is corrected data, where each pix-
el responds consistently across the detector input range, creating a uniform image.
Figure 8.1 Digital process showing the application of NUC tables.
To create the NUC table, the camera images either one or two uniform temperature sour-
ces. The source is an external source provided by the user. The source should be uni-
form and large enough to overfill the camera’s field of view. By analyzing the pixel data
from these constant sources, the non-uniformity of the pixels can be determined and cor-
rected. There are two types of processes that are used to create the NUC table: one
point and two point.
8.1.2 CNUC
8.1.2.1 General
CNUC is a proprietary calibration process. A camera calibrated with CNUC allows for
flexible integration time adjustments without the need to perform NUCs. Additionally, the
CNUC calibration produces accurate measurement stability regardless of the camera’s
exposure to ambient temperature variations.
A CNUC correction is valid for a specific optical configuration comprising a lens and
spectral filters combination. CNUC corrections are generated by FLIR service offices
where advanced calibration benches are available. Contact your FLIR representative for
CNUC correction on new spectral filters or infrared lenses.
The CNUC process generates a gain and offset map based on the camera’s internal pa-
rameters and environmental probes.
8.1.3 Two-point correction process
8.1.3.1 General
The two-point correction process builds a NUC table that contains individually computed
gain and offset coefficients for each pixel, as shown in Figure 8.2. Two uniform sources
are required for this correction: one source at the low end of the usable detector input
range, and a second source at the upper end.
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