Panasonic A230, Руководство пользователя, Страница: 212 / 377

Gray Scale Edge Checkers OCR Type A230
11 − 6
11.1 Gray Scale Edge Checkers
24. Area
Create or move the checker area.
The area cannot be set to a size of less than 7 pixels in the scanning direction.
The “Illegal checker area size.” error will appear.
25. Edge Condition
Set the edge conditions for the checker being created.
A gray scale edge checker scans from start point to end point, detecting edges
in the image under inspection where light changes to dark, or where dark
changes to light, or both.
The edges are detected at locations meeting the conditions set for the edge
threshold value.
The default setting is Both . When set to Both , the filter, width and average
area functions work on both light to dark edges and dark to light edges,
enabling edges with positive and negative differentials to be detected.
Edge condition
Point
Scan direction
Detection direction = horizontal
Detection direction = vertical
Finishing point
Dark
→
light
Light
→
dark
Starting point
Scan direction
Detected Detected Detected
Detected
Detected
Detected
Dark
→
light
Light
→
dark
Starting point
Finishing point
Both
Both
26. Edge Threshold Value
Set the edge threshold values for the checker being created.
A gray scale edge checker performs differential processing on a gray scale
image to detect edges. Changes in brightness of the gray scale image are
processed as differential data. After processing, the data can be represented
as a graph with peaks like those shown in the diagram. When the graph slants
upwards, the gray scale level is changing from dark to light. The dotted line
on the vertical axis of this graph is the threshold value (expressed in
256 − gradation gray scale). Only peaks which reach the threshold value are
detected as edges. Set the threshold value with reference to the differential
values of the edges so that only the required edges are detected.