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Grey values of picture elements (pixels) obtained by step scans perpendicular to the edge are summed, and adjacent sum values are subtracted to detect edge irregularities.
English (United States)
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Edge Analysis in Digitized Grey Level Patterns. November 1982
Grey values of picture elements (pixels) obtained by step scans
perpendicular to the edge are summed, and adjacent sum values are subtracted
to detect edge irregularities.
In Fig. 1, the edge 21 to be traced separates a (dot-marked) dark pattern
area from a bright area. The pattern is digitized into square pixels (e.g., 2Oa),
each having one of 128 grey levels represented by a pixel byte in a digital image
The meander-shaped scanning path 22 is followed by generating appropriate
image storage addresses and reading the corresponding pixel grey values. The
start and end points TH of each scanning section perpendicular to the edge are
such that they are outside the edge transition area and well within the bright and
dark intensity levels, respectively. The grey values of the remaining pixels (e.g.,
2Ob, 2Oc, 2Od) are added to form sum E(1). Adjacent sum values along the
edge direction are then subtracted (e.g., E(1) - E(2) equals D(1)). If edge 21
extends along its nominal horizontal direction and has no defects, the difference
D is zero; small defects, e.g., indentation 23 or deviations from the nominal edge
direction (e.g., angle o(Lambda), lead to D values unequal zero.
The use of grey levels in the summation process reveals local edge defects
which are smaller than the pixel area (e.g., indentation 23), so that edge analysis
with high resolution is available without decreasing the pixel size...