Imperx Cheetah 3G-SDI User Manual page 95

Cheetah Pregius Camera User Manual | 3G-SDI Interface
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:
1
���� ( ���� ) =
1 + ����
−���� ( ����−���� )
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).
original signal
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.
April 14, 2021
sigmoid corrected signal
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Rev 1.4