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4 Functionality
4.3.4 Gray Level Transformation (LUT)
Gray level transformation is remapping of the gray level values of an input image to new
values. The look-up table (LUT) is used to convert the grayscale value of each pixel in an image
into another gray 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 gray levels can be
mapped to 256 output gray levels. The use of the three available modes is explained in the
next sections.
The output gray level resolution of the look-up table (independent of gain,
gamma or user-definded mode) is always 8 bit.
There are 2 predefined function, which generate a LUT 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. 4.17). It is configurable in the
range from 1.0 to 4.0. (e.g. 1.234)
300
250
200
150
100
50
0
0
Figure 4.17: Applying a linear gain to an image
28
Gray level transformation − Gain: y = (255/1023) ⋅ a ⋅ x
200
400
x: gray level input value (10 bit) [DN]
600
800
a = 1.0
a = 2.0
a = 3.0
a = 4.0
1000
1200
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