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AG (Average Grade of Damage across many parts of the Finder Pattern)
is a grade that considers the
accumulated effect of damage to several parts of the finder pattern. Five values are averaged together. One of
these is the lowest of all the grades associated with all the clock track segments, namely TCT, TTR, TQZ and
RCT, RTR, RQZ. The other four are LLS, BLS, LQZ, and BQZ. The average must fall in the range of 0.0 through
4.0 and is given a grade according to the following:
Ave Grade
Grade
Equals 4.0
A (4.0)
≥ 3.5 (but less than 4.0)
B (3.0)
≥ 3.0 (but lessthan 3.5)
C (2.0)
≥ 2.5 (but less than 3)
D (1.0)
< 2.5
F (0)
Note
: The effect of the AG parameter is to lower the overall grade of symbols, which have several individual
parameters at or near the same level. For example, with enough B grades in individual parameters, the overall
grade may come out as a C grade rather than a B.
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DECODE
: Reports whether the 2D Symbol is decoded in accordance with the reference decode algorithm with
the specified aperture.
Note
: It is possible to report decoded results, but for a failure to occur when decoding in accordance with the
reference decode algorithm. In this case, the DECODE grade is F (0).
Contrast Uniformity (CU)
is the value of MOD (modulation) for the worst case module selected from a 2D Matrix
symbol. This is useful for process control, as way of measuring the drift in reflectivity consistency, and for testing
conformance to ISO/IEC 15426-2, which requires the modulation of a specific module within a conformance test
symbol to be reported. This parameter is reported in General Characteristics.
ISO 29158 (AIM-DPM) 2006 Grading Parameters
The ISO 29158 (AIM-DPM) method of grading Data Matrix symbols modifies the process of ISO-15415 and is appropriate
for direct part marking applications. This standard is more representative of the scanning performance of modern readers
that are designed in some cases for these demanding applications. In this method, the image brightness is adjusted to
produce an image of the symbol that fills most or all of the dynamic range of the imager, resulting in an image that is easy
to see. The threshold between dark and light is calculated from the statistics of the image brightness histogram.
Therefore, the measurements calculated by AIM-DPM differ from those of ISO 15415 significantly. Some of the
parameters reported in ISO 15415 are changed so drastically and are renamed to avoid confusion between the two
methods:
AIM-DPM Parameter
Name
ISO 15415 Parameter
Name
Summary of Change(s)
CC (Cell Contrast)
SC (Symbol Contrast)
Made relative to light background.
CM (Cell Modulation) MOD (Modulation)
Threshold calculated from statistics rather than the maximum and
minimum reflectance. Grading scale range set to Mean of distribution,
rather than maximum and minimum reflectance.
DD (Distributed
Damage)
AG (Average Grade)
Modulation overlay uses only A, B, D, and F levels instead of A, B, C, D,
and F.
MR (Minimum
Reflectance)
Not necessary, since
SC is measured on an
absolute scale.
An absolute limit on SC of 5% added to temper the relative nature of CC
and “catch” extremely low contrast symbols.
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Grading Standards and their Parameters