1. Edge Determination
- is the image of the bar code as it is perceived by a
moving aperture, such as a laser beam or a bar code wand. The
scan reflectance profile is a measurement of spots and voids
(called "defects") as well as contrast and other
parameters.
2. Minimum
Reflectance - checks that the darkness of the bars is
sufficient. The amount of light reflected by the bars (bar
reflectance) must be less than half the light reflected by the
spaces (space reflectance).
3. Symbol Contrast
- measures the contrast between the brightest space and the
darkest bar. The result is assigned a letter grade of A,B,C,D or
F, with A being the highest contrast.
4. Minimum Edge
Contrast - checks that the contrast between adjacent bars
and spaces is high enough.
5. Modulation - checks the worst case
dip in contrast any place in the bar code. If all bars and
spaces are the same brightness, modulation would be equivalent
to symbol contrast, or 100 percent. If some spaces are less
bright than the brightest one, modulation will be some fraction
of the overall contrast. The percentage is assigned a letter
grade. Excessive ink spread can result in low modulation because
very narrow spaces appear to be filled in by the encroaching
bars in the scan reflectance profile. This very serious issue
for scanner was not directly addressed by Traditional
verification techniques.
6. Defects - the worst case change in
darkness within a single bar or space. The largest difference in
reflectivity found in a single bar or space is measured as a
percentage of the Symbol Contrast and assigned a letter
grade.
7. Decode - the widths of each bar and
space is measured and used to interpret the number content of
the bar code according to a specific mathematical formula
appropriate for the bar code type. This formula must be
specified, such as by the UCC Quality Specification for the UPC
Printed Symbol, to apply to ANSI method to new types of bar
codes. If the bar code cannot be decoded according to the
formula, the accuracy of the bar and space widths
are inadequate.
8. Decodability - the formula used for
Decode is further analyzed to see how accurate the bar and space
widths are. A perfectly accurate bar code will have 100 percent
decodability, but decodability as low as 25 percent is often
acceptable. This measure helps track degradation in printing
plates and gives early warning while there is still plenty of
room for more degradation.
9. Quiet Zone - this checks for
adequate space on the left and right of the bar code. Often a
design oversight violates the requirements for adequate space,
but generally this is not something that would fluctuate during
a print run.
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