CAMERAS FRAME GRABBERS IMAGING SOLUTIONS
BOBCAT Hardware User’s Manual
IMPERX
Rev. 2.0.9
6421 Congress Ave.
4/8/2014
Boca Raton, FL 33487
www.imperx.com
+1 (561) 989-0006
190 of 329
2.15 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
2.15.1 Standard Gamma Correction
The image generated by the camera is normally viewed on a CRT (or LCD) display,
which does not have a linear transfer function – i.e., the display brightness is not
linearly proportional to the scene brightness (as captured by the camera). As the
object brightness is lowered, the brightness of the display correspondingly lowers.
At a certain brightness level, the scene brightness decrease does not lead to a
corresponding display brightness decrease. The same is valid if the brightness is
increased. This is because the display has a nonlinear transfer function and a
brightness dynamic range much lower than the camera. The camera has a built-in
transfer function to compensate for this non-linearity, which is called gamma
correction. If enabled, the video signal is transformed by a non-linear function close
to the square root function (0.45 power) – formula 2.4. In the digital domain this is a
nonlinear conversion from 12-bit to 12-bit – Figure 2.31.
Output signal [V] = (input signal [V])
0.45
(2.4)