FLIR LWIR, Примечание к применению

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FLIR Camera Adjustments
102-PS242-100-01
Rev110 June 2014 Page 8 of 28
The linear histogram algorithm performs a linear transformation from 14-bit to 8-bit of the form:
8bit
i
= m * 14bit
i
+ b
The slope of the transformation is computed automatically based on the ROI histogram:
m = 255 / (14bit_(100 – Tail Rejection)% - 14bit_(Tail Rejection)%),
where 14bit_(Tail Rejection)% is the 14-bit value corresponding to the user selectable tail rejection
percentage point on the cumulative ROI histogram and 14bit_(100 – Tail Rejection)% is the value
corresponding to the difference between 100% and the user selectable tail rejection percentage point in
Tau 2.7 and Quark 2.0.
The offset is then computed as
b = ITT midpoint - avg(14bit_(100 – Tail Rejection)%, 14bit_(Tail Rejection)%),* m
In other words, the algorithm attempts to map the midway point between the top and bottom tail rejection
points on the cumulative histogram to the specified ITT midpoint, as shown in Figure 4 for the case in
which the tail rejection parameter selected is 5%. The 8-bit values resulting from the above equations are
clipped to a minimum value of 0 and a maximum value of 255.
(a) ITT Midpoint = 128
(b) ITT Midpoint = 96
Figure 4: Illustration of the Linear-Histogram Mapping Function
2.3 Plateau Histogram Equalization
The Plateau Histogram Equalization algorithm seeks to maximize the dynamic range available for the
content of the scene. It does this using a transfer function that is based on the number of pixels that are in
each bin and allocating more 8-bit range for that bin. The Plateau value is the pixels/bin limit when the
transfer function is maximized. When this number is small, the Automatic AGC will approach a linear
algorithm that preserves a linear mapping between the 14-bit and 8-bit data. The goal of the Automatic
algorithm is to try and make each of the 255 bins have the same number of pixels in it, which should give
the best contrast for the given scene. When the plateau value is higher, the algorithm is more able to
14bit_5% 14bit_95%
Avg(14bit_5%, 14bit_95%)
specified
ITT Midpoint
14bit_5%
14bit_95%
Avg(14bit_5%, 14bit_95%)
specified
ITT Midpoint