BOBCAT Hardware User’s Manual
Imperx, Inc.
Rev. 1.0
6421 Congress Ave.
5/4/2010
Boca Raton, FL 33487
+1 (561) 989-0006
99 of 212
2.14.1 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)
Figure 2.31 – Gamma corrected video signal
2.14.2 User Defined LUT
The user can define any 12-bit to 12-bit transformation as a user LUT and can
upload it to the camera using the configuration utility software. The user can
specify a transfer function of their choice to match the camera’s dynamic range to
the scene’s dynamic range. There are no limitations to the profile of the function.
The LUT must include all possible input values (0 to 4095) – Figures 2.32.
