© 2016 Thorlabs Scientific Imaging
2 Camera Basics
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Such a gamma characteristic brightens dark areas of an image, which corresponds more to the
perception of the human eye. In light areas of an image, the differences in brightness are
condensed for this.
Image with linear characteristic
Image with gamma characteristic
Logarithmic characteristic
The effect of the logarithmic characteristic is even stronger. Here, the characteristic follows the
function
The following diagram illustrates how very large jumps in brightness in light areas of a scene only
cause small changes in image brightness. This explains why image sensors with a logarithmic
characteristic, in particular, are ideal for imaging scenes with very high dynamic range.
Imaging with logarithmic characteristic
Lookup table (LUT)
With a lookup table (LUT) it is easy to apply characteristic curves to digital images. A LUT is a
table which assigns an output value to every possible input value. The figure below shows a LUT
which would binarize an image: For an 8 bit image, for example, this LUT would replace all pixels
with gray values 0...127 with value 0 and all pixels with gray values 128...255 with value 255.
Using LUTs has the advantage that calculations can be done very fast. Typical applications of
LUTs are enhancing image contrast, or gamma characteristics.
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