Welch Allyn Scanteam 3700PDF, Техническое руководство

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Printing PDF417 Labels C–3
C.3.3 Tolerance to Label Damage
The more tolerance to label damage, the easier the label is to scan. Increasing the error
correction level helps. Even when the label has no damage, the error correction can help
fill in any missing codewords. In traditional bar codes, row height provided tolerance to
label damage. The encoded information is repeated over the height of the row. Even
with some damage it is possible to find a good scan path.
Error correction levels 0–2 are not recommended since they tolerate very few errors and
scanning is difficult. Error correction levels 7–8 are not recommended since they add a
great deal of area to the label. Welch Allyn suggests using error correction levels 3–6,
depending on the message size. These levels offer excellent protection from label
damage without adding a great deal of area to the label.
C.4 Suggestions for Maximum Readability
C.4.1 Making X Dimension as Small as Possible
Reducing the X dimension will improve readability by increasing the maximum tilt
angle. Welch Allyn CCD readers can easily resolve elements 6.6 mils wide. Many
printers can accurately print at that density since it is a derivative of 300 dots per inch.
C.4.2 Making Y Dimension as Large as Possible
Increasing the Y dimension improves readability by:
1. Increasing the maximum tilt angle
2. Allowing higher scan speeds
3. Providing slight tolerance to label damage since the encoded information is repeated
over the height of the row
Unfortunately an increase in row height means a decrease in information density.
Readability and information density are both important. You will need to determine the
needs of your particular application. In any case, you should make the row height as
large as space allows. If necessary, try increasing the number of columns to match the
width of the scanner. Since fewer rows may then be needed, they may be printed taller.
C.4.3 Choosing Error Correction
Choose the error correction level so that the number of error correction codewords is
about 15–25% the number of message codewords. Increasing error correction level
generally improves readability. Where space is limited, however, it may be more of an
advantage to use a lower error correction level and instead increase the Y dimension.
Increasing error correction level means decreasing information density. Readability will
greatly improve in going from level 0 to level 3. The information density will not
change much.