Cheetah KAC Camera User Manual | Camera Link (CLF) Interface
October 1, 2019
Page
117
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135
Rev 7.2
5.17 Transfer Function Correction – User LUT
The user defined LUT (Lookup Table) feature allows you to modify and transform the
original video data into any arbitrary value (Figure 73). You can transform any 12-bit value
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 first LUT is factory
programmed with a standard Gamma 0.45. The factory does not pre-program the second
LUT. You can modify both LUTs (Appendix B - Creating Look-up Tables) and upload your
custom LUT using the Cheetah configuration software.
Figure 73: Lookup Table.
5.17.1 Standard Gamma Correction
The image generated by the camera normally appears for viewing on a monitor. However,
the monitor image does not have a linear transfer function, that is, the display brightness
is not linearly proportional to the scene brightness captured by the camera. As the object
brightness dims, 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 called
gamma correction. If enabled, the video signal transforms by the following non-linear
function close to the square root function (0.45 power). In the digital domain, this is a
nonlinear conversion from 12-bit to 12-bit (Figure 74).
Output signal [V] = (input signal [V])
0.45
(2.4)
Figure 74: Gamma Corrected Video Signal.
