HandHeld Entertainment Quick Check PC600 - Manual (Page 37)

Numeric ranges exist within the alphabetic grades. Use of the numeric
equivalents may provide greater assistance in determining symbol problems.
The following illustration shows a Scan Reflectance Profile from a Quick Check ®
PC scan of a symbol.
To differentiate bars and spaces, a Global Threshold is established on the scan
reflectance profile by drawing a horizontal line half way between the highest
reflectance value and the lowest reflectance value seen in the profile. The
illustration above shows the Global Threshold for the Scan Reflectance Profile.
The Global Threshold is calculated as the lowest reflectance value (typically a
bar) plus one-half the overall symbol contrast. Global Threshold is a Pass/Fail
parameter.
GT = Rmin + SC/2
Once the Global Threshold is determined, Edge Determination is performed on
the Scan Profile. An edge is performed by determining the number of lines in the
profile that cross the Global Threshold. If the number of crossings matches a
valid bar code pattern, the symbol will pass Edge Determination. However, if
there are serious defects and a low overall symbol contrast, the defects (spots or
voids) will appear to be bars or spaces. This will render a Failing grade. Edge
Determination is a Pass/Fail parameter.
Minimum Reflectance (Rmin) is a basic measure in the ISO/IEC method and
reported in the Reflectance Parameters section of the Quick Check
® PC screen.
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