BOBCAT Hardware User’s Manual
Imperx, Inc.
Rev. 1.0
6421 Congress Ave.
5/4/2010
Boca Raton, FL 33487
+1 (561) 989-0006
98 of 212
2.13 DYNAMIC BLACK LEVEL CORRECTION AND TAP BALANCING
Black Level Correction
As was described in the Gain and Offset section, the reference black level on each CCD
output fluctuates around 0V. The AFE offset correction works on the entire image and if
there are noise fluctuations on a line level, the AFE is not capable of correcting them. The
camera has a built in dynamic signal-to-noise correction feature to compensate for this
effect. In the beginning of each line the CCD has several back (masked) columns. The dark
level for each tap is sampled over several of these masked pixels and the average per tap
black level floor is calculated for each frame. The average floor level for each tap is then
subtracted from each incoming pixel (from the corresponding tap) from the next frame.
Tap Balancing
Since the camera has two separate video outputs coming out of the CCD, there is always
some offset misbalance between the video outputs. Thus, changing the AFE gain leads to a
change in the offset level and to a further misbalance between the two video signals. To
correct the balance between two signals at any particular gain, BOBCAT series of cameras
have static and dynamic balancing algorithms implemented in the firmware. The
algorithms compares the black and bright levels of the adjacent pixels around the tap line,
and adjusts the gain and offset for each tap accordingly, until the balance has been reached.
The selection to use static or dynamic balancing depends on the application. Please note,
that if AGC is enabled, it is strongly recommended to use static balancing, because the
dynamic balancing can interfere with the AGC algorithm.
2.14 TRANSFER FUNCTION CORRECTION – USER LUT
The user defined LUT (Lookup Table) feature allows the user to modify and transform the
original video data into any arbitrary value – Figure 2.30. Any 12-bit value can be
transformed into any other 12-bit value. The camera supports two separate lookup tables,
each consisting of 4096 entries, with each entry being 12 bits wide. The LUT is applied to
the entire image unless AOI8 is enabled as “LUT ROI”. In this case the LUT function will
apply only to the selected ROI. The first LUT is factory programmed with a standard
Gamma 0.45. The second LUT is not pre-programmed in the factory. Both LUT’s are
available for modifications, and the user can generate and upload his own custom LUT
using the BOBCAT Configuration software – refer to Appendix B.
LUT
12 bit input
data
12 bit output
data
Figure 2.30 – Look up table
