© 2016 Thorlabs Scientific Imaging44
DCx Camera Functional Description and SDK Manual
2.5 Digitizing Images
Characteristics and LUT
Bit depth and digital contrast adjustment
2.5.1 Characteristics and LUT
When perceiving or imaging a scene, the form of the imaging characteristic is crucial for displaying
the differences in brightness. With image processing (e.g. applications such as edge detection
and character recognition), linear characteristics are generally required. The human eye, on the
other hand, perceives differences in brightness based on a logarithmic characteristic, which often
approximates a gamma characteristic in practice. All three forms will be shown in the following.
Linear characteristic
If a system (e.g. a camera with a conventional CCD sensor) yields double the output value for
double the brightness, the system features a linear characteristic:
Imaging with linear characteristic
Gamma characteristic
Gamma characteristics (or gamma curves) are named after the Greek formula symbol γ. Gamma
curves are power functions of the form
and are often used in photography or image display on computer screens. A gamma value of 1
generates a linear characteristic again. A curve with the value γ = 2.2 used for computer screens is
shown in the figure below.
Imaging with gamma characteristic
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