8-11
8 Advanced Settings
MicroHAWK V320-F / V330-F / V420-F / V430-F Barcode Reader User Manual
8-6 I/O
8
8-6-2 Symbol Grading
To illustrate how variation that appears subtle to the eye can have a large impact on grading
performance consider the following image from a standard reader using internal illumination. The scan
reflectance profile for two line scans in the image are shown to the right of the imaged symbols. The
larger symbol which spans the entire field of view shows dramatic differences. The spaces in the center
of the symbol are providing 50% more signal response then the quiet zones at either edge of the field of
view. Similarly, the smaller symbol lower in the field of view provides a much lower overall response
throughout its region. Scenarios like this will create low modulation scores and differences in defect
scores depending on the physical location of the defect. Worse yet if the symbol is moved within the
field of view it will receive different scores. It is recommended that external illumination is used and
evaluated closely for response characteristics when using ISO 15416 grading.
Uneven Illumination
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.
Scan Line Aperture
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