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The following is an example line profile of a bare image of a white uniform object:
Whether a line profile is good or not is mainly determined by two factors:
1. Flatness
2. Height
1) Flatness: As line profiles represent a flat field in this case, the flatter the better it is. However,
due to the lens-shading effect, the light falls-off towards the edges and results in edges output
lower than the central area output. This leads to the edges' noise level being higher than the
central area within FFC applied images. A smaller aperture opening and longer focal length can
reduce the lens-shading effect. In some demanding applications, optimized low-shading lenses
should be considered.
2) Height: The closer the average output level is to your calibration target the better. It is okay if
the level is higher than the target, but it is not desirable to be much lower than the target.
Compared to the target, an extremely low output will increase the noise level significantly high
after the PRNU is corrected such that the SNR and/or DNR may not meet your application's
requirements. To avoid this, the profile should reach a level as near the calibration target as
possible.
In order to adjust the profile height the exposure time, light intensity, diaphragm opening (which
may conflict with the flatness), and lens throughput index, etc. are all factors that need to be
considered. The purpose of all these is to enhance the illumination, after all.
Linea GigE Series Camera
Line profile of a bare image of a white and uniform object.
Operational Reference • 63
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