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4.3.2 Grey Level Transformation (LUT)
Grey level transformation is remapping of the grey level values of an input image to new
values. The look-up table (LUT) is used to convert the greyscale value of each pixel in an image
into another grey value. It is typically used to implement a transfer curve for contrast
expansion. The camera performs a 10-to-8-bit mapping, so that 1024 input grey levels can be
mapped to 256 output grey levels. The use of the three available modes is explained in the
next sections.
The output grey level resolution of the look-up table (independent of gain,
gamma or user-definded mode) is always 8 bit.
There are 2 predefined functions, which generate a look-up table and transfer it
to the camera. For other transfer functions the user can define his own LUT file.
Gain
The ’Gain’ mode performs a digital, linear amplification (see Fig. 4.7). It is configurable in the
range from 1.0 to 4.0 (e.g. 1.234).
0 200 400 600 800 1000 1200
0
50
100
150
200
250
300
Grey level transformation − Gain: y = (255/1023)
⋅
a
⋅
x
x: grey level input value (10 bit) [DN]
y: grey level output value (8 bit) [DN]
a = 1.0
a = 2.0
a = 3.0
a = 4.0
Figure 4.7: Applying a linear gain to an image
4.3 Pixel Response 25