Chapter 9
Data Correction
71
9.4
Defect/Blemish Correction
All NIRvana HS cameras have a defect map pre-loaded into camera NVRAM. LightField
creates a Blemish Definition file to correct for any inherent defects/blemishes that have
been identified on the sensor by Teledyne Princeton Instruments. If additional
corrections are required, customers can manually edit this Blemish Definition File.
Defects in general are outlying pixels whose sensitivity to light is too low (dark defects)
or too high (white defects). These pixels may have static behavior or vary over time (e.g.
flicker) and may depend on speed or gain.
REFERENCES:
Refer to the LightField Online Help for complete
information about how to modify and store the Blemish
Defect File.
The following types of defects/blemishes are corrected:
•
Row;
•
Column;
•
Point; and
•
Cluster.
Beginning with NIRvana HS, a new geometry of sensor defect, called a Star defect, is
now able to be identified and corrected.
A Star defect is a square 3 x 3 pixel region described as a white cross with a black center
pixel. The four corners of the 3 x 3 matrix may be fuzzy/gray. This defect is caused by
charge that cannot be absorbed by a dead pixel and ultimately spills into surrounding
pixels in a star pattern. See
for a simplified representation of a Star defect.
Figure 9-3: Typical Star Defect (Not to Scale)
Using a complex series of correction algorithms, LightField is able to create an accurate
approximation of acquired image data for this region.
Although theoretically possible, unlike with the simpler geometric defects (e.g., row,
column, etc.,) Teledyne Princeton Instruments discourages the manual modification of
the NIRvana HS Defect Map for any Star Defects that have not previously been
identified by the factory. Contact Teledyne Princeton Instruments Customer Support
for guidance if additional Star Defects must be corrected. Refer to
on page 100 for complete information.
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