LYNX Manual RA02
2.9
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 2.46. Any 12-
bit value can be transformed into any other 12-bit value. The camera supports two
separate lookup tables, each consisting of 2048 entries, with each entry being 12
bits wide. The first LUT is factory programmed with a standard Gamma 0.45
correction – see section 2.9.1. 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 LynxTerminal software – refer to
Appendix B.
LUT
12 bit input
data
12 bit output
data
Figure 2.46 - Look Up Table
2.9.1
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 9.1. In the digital domain this is
a nonlinear conversion from 12-bit to 12-bit – Figure 2.47. If the camera
resolution is set to 8-bit or 10-bit, the camera will truncate the corresponding
LSBs (see section 2.8).
Output signal [V] = (input signal [V])
0.45
(9.1)
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