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128
Software Module
Number of
Scanlines
Maximum number of scanlines used during the scanning of a (candidate) bar code. If
’Number of Scanlines’ is not set (the parameter has a value of 0) the maximum number
of scanlines is determined internally and it will be 10 for all single-row bar codes, 20
for RSS-14 Stacked Omnidirectional, respectively, and 55 for RSS Expanded Stacked.
With this parameter, you can improve performance in two cases. In the first case, the
image contains many false candidates. While the bar code itself is usually decoded
after one or two scans (except for stacked bar codes, see below), a false candidate is
scanned with the default value of 10 scanlines, which increases the runtime unneces-
sarily. Reducing the number of scanlines can therefore improve performance in imag-
es with many false candidates. As a rule of thumb, images with higher quality need less
scanlines than images of lower quality. For an average image, a value between 2 and 5
should be sufficient. If a bar code can, however, not be detected after reducing the
number of scanlines, the number has to be increased again. The second case con-
cerns stacked bar codes (currently RSS-14 Stacked, RSS-14 Stacked Omnidirectional,
and RSS Expanded Stacked). Here, all scanlines are evaluated, in contrast to single-
row bar codes (e.g., Code 128, EAN 13, or RSS Limited) where the scanning stops
after the code is decoded successfully. Since the scanning of the scanlines is actually
one of the most time consuming parts of the bar code algorithm, adjusting ’Number of
Scanlines’ might result in essential performance improvements.
This is especially valid for RSS Expanded Stacked. A RSS Expanded Stacked symbol
might have up to 11 rows and therefore 55 scanlines are required to robustly detect
all of them. If only symbols with smaller number of rows are expected, one can reduce
’Number of Scanlines’ leaving 1.5 to 5 scanlines per row.
Typical values: [0, 5, 10, 20 . . . ] Default: 0
Min Identical
Scanlines
Minimum number of successfully decoded scanlines, which return identical data, for
a decoding of a bar code symbol to be accepted. If this parameter is not set (has a
value of 0) a bar code is considered decoded with the first scanline, which was suc-
cessfully decoded (in the case of stacked codes, it must be a successful scanline per
symbol row). Increasing this parameter to 2 or more is particularly useful, when it has
to be prevented that a bar code is detected accidentally. This can typically happen if
a scanline extracted erronous or false edges out of a low quality image or in a very
noisy image fragment. This parameter reduces the false detection also in cases where
a specific bar code type is searched for in an image containing symbols from other bar
code symbologies. Typical values: [0, 2, 3, . . . ] Default: 0
Orientation
Expected bar code orientation. A potential (candidate) bar code contains bars with
similar orientation. The ’Orientation’ and ’Orientation Tolerance’ parameters are used
to specify the range [’Orientation’- ’Orientation Tolerance’, ’Orientation’+’Orientation
Tolerance’]. The bar code algorithm processes a candidate bar code only when the
average orientation of its bars lies in this range. If the bar codes are expected to appear
only in certain orientations in the processed images, one can reduce the orientation
range adequately. This enables an early identification of false candidates and hence
shorter execution times. This adjustment can be used for images with a lot of texture,
which includes fragments tending to result in false bar code candidates. The reading
direction of the bar codes is ignored, which results in relevant orientation values only
in the range [-90.0 . . . 90.0]. Typical values: [-90.0 . . . 90.0]
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