Omron V440-F User Manual page 210

 Synthetic Aperture
The synthetic aperture is a process in ISO 15416 that is applied to the image when extracting the
scan line profile for grading. The aperture is an averaging process using a circular region along the
scan line shown below in Figure 2.
Figure 2: Scan Line Aperture
This averaging provides a generalization of the information in the image that is consistent with typi-
cal reading equipment acquisition techniques. Verification systems implement the aperture based
on the physical dimension of the symbol under test and the application standard guidelines, such as
GS1. In a reader that may have varying optical configurations and no calibration process, there is no
means by which the process can determine the physical size of the symbol under inspection. For
this reason the aperture is a configurable parameter as a percentage of the nominal dimension of
the symbol under evaluation. The default value provides a general case that is close to most appli-
cation standards. It is the user's responsibility to ensure this percentage matches the grading objec-
tives. A representation of the effects of the aperture is provided in Figure 3. A larger aperture
configuration creates more of an averaging effect that is less sensitive to defects but may lower
modulation.
Figure 3: Aperture Effects
 Overall, Scan, and Individual Parameter Grades
The overall grade is calculated in accordance with the process defined in ISO 15416. This is often
misunderstood, so a review is provided here. The overall grade is an average of the individual scan
grades that are applied over the inspection region. The individual scan grades are not provided by
the reader but are calculated internally. These individual scan grades are the lowest grade of any
single parameter grade evaluated in that particular scan line or 0 / F if the scan line evaluation fails
the edge determination or quiet zone requirements. The individual parameter grades that are pro-
vided by the reader are averages of the individual parameters grades from each scan evaluated.
These individual average parameter grades are not themselves part of the overall grade calculation
but can be helpful for diagnosing the cause of declining overall grades. This creates circumstances
in which the overall grade can be lower than the lowest average grade, particularly when there are
degrading features in the symbol from different parameters.
V440-F C-Mount Code Reader User Manual
8 Advanced Settings
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