Balluff MATRIX VISION mvBlueFOX Series, Technical Manual

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1.18 Use Cases 109
1.18.2.1.5 List-based defect Pixel correction on the camera As described before, it is possible to upload lists
of defect pixel onto the camera. Different algorithms can be used to determine whether a pixel is defective or not,
which is dependent of how much it is allowed a pixel to deviate, temperature, gain, and exposure time. As described
before, the list-based correction is deterministic, meaning it is exactly known which pixels will be corrected.
Anyhow, the list-based correction has some disadvantages:
• A default list is stored in the camera during production, but this might to fit to the target application because
of much different temperature / exposure time setting
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It is necessary to create the list using a detection algorithm (or mvIMPACT Acquire support)
• During time and sensor aging, new defects could/will appear
• It doesn’t work in binning/decimation modes
• The memory for storing defective pixels is limited
1.18.2.1.6 Adaptive / algorithm-based correction on the camera In this case, the camera performs detection
and correction on-the-fly without using any defect-list.
The adaptive correction addresses the above-mentioned disadvantages of the list-based method. While the correc-
tion itself (this is which pixels are used to correct an identified defect) is the same, no static information from a list is
used, instead they are detected "on the fly".
To use reasonable thresholds, knowledge of the noise statistics of the sensor is used to detect the outliers. These
will be corrected also on the fly. Because this is a dynamic approach, it also works in binning/decimation modes
and would also detect new appearing defects.
Nevertheless, there are some disadvantages:
• It is non-deterministic
• Wrong positives can be detected, meaning non-defect pixels could be treated as defect
• If pixels are at the edge of the used thresholds, it could be corrected in one frame, but not in the next
On mvBlueFOX3 cameras, the adaptive correction is always used if:
• There is no list stored on the camera
• Binning or decimation is used
1.18.2.1.7 Flat-Field Correction
Each pixel of a sensor chip is a single detector with its own properties. Particularly, this pertains to the sensitivity
as the case may be the spectral sensitivity. To solve this problem (including lens and illumination variations), a plain
and equally "colored" calibration plate (e.g. white or gray) as a flat-field is snapped, which will be used to correct
the original image. Between flat-field correction and the future application you must not change the optic. To reduce
errors while doing the flat-field correction, a saturation between 50 % and 75 % of the flat-field in the histogram is
convenient.
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