Photon Focus CameraLink MV1-D1312 series User Manual page 34

4 Functionality
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Figure 4.19: Schematic presentation of the offset correction algorithm
How to Obtain a Black Reference Image
In order to improve the image quality, the black reference image must meet certain demands.
• The black reference image must be obtained at no illumination, e.g. with lens aperture
closed or closed lens opening.
• It may be necessary to adjust the black level offset of the camera. In the histogram of the
black reference image, ideally there are no grey levels at value 0 DN after adjustment of
the black level offset. All pixels that are saturated black (0 DN) will not be properly
corrected (see Fig. 4.20). The peak in the histogram should be well below the hot pixel
threshold of 252 DN @ 10 bit.
• Camera settings may influence the grey level. Therefore, for best results the camera
settings of the black reference image must be identical with the camera settings of the
image to be corrected.
Figure 4.20: Histogram of a proper black reference image for offset correction
Hot pixel correction
Every pixel that exceeds a certain threshold in the black reference image is marked as a hot
pixel. If the hot pixel correction is switched on, the camera replaces the value of a hot pixel by
an average of its neighbour pixels (see Fig. 4.21).
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