Cheetah Pregius Camera with 10 GigE Vision Interface – User Manual
October 8, 2020
Page
166
of
170
Rev 1.0
6.
For a color camera, you can set a transfer function for each channel. Use R, G, and B tabs on
the left to switch between the channels.
7.
To save the LUT file, go to
File > Save as….
Example
A modified sigmoid function can be used to enhance low contrast images. The modified sigmoid
function is given below:
𝐹𝐹
(
𝑥𝑥
) =
1
1 +
𝑒𝑒
−𝑎𝑎
(
𝑥𝑥−𝑏𝑏
)
where
x
is the input pixel value.
a
is a contrast factor. It determines the steepness of the curve (0.5 – low gain; 10 -high gain).
b
is a threshold level. It determines a sigmoid’s midpoint. A midpoint is the brightness of input
pixels that is used as a reference. If the brightness of an input pixel is higher than a midpoint, the
output pixel value is increased. Otherwise, the output pixel value is decreased.
In the LUT Manager window, type in the following formula under the
Formula
control (with a=4
and b=2):
4095*(1/(1+(exp(-4*(x/(4095/4)-2)))))
The function is scaled so that the input and output pixel values are within the range from 0 to
4095 (for a 12-bit image).
To adjust the overall brightness and contrast of the image, use both threshold and contrast
factor parameters. The threshold value controls the amount of brightness, and the contrast
factor controls the difference between pixels.
original signal
sigmoid corrected signal
