Banner PresencePLUS Pro COLOR—PROII Camera - Manual (Page 143)

When adding an ROI for a Circle Detect too, click near the center of the circle you wish to inspect and drag to the
outside of the circle. Adjust the inner and outer rings of the ROI by dragging the squares on the top, bottom, and sides.
If using the "Circular, Arc" option, adjust the angular range by dragging the lines at the start and end of the arc.
Edges
Threshold measures the rate of change of grayscale values and needs sharply-defined transitions. The Circle Detect
tool finds edge points by scanning along many invisible lines from inside of the ROI to the outside. Arrows on the
ROI point outwards to indicate this direction. Three settings—Threshold, Polarity, and Sample Rate—give you control
over how the edge scan works.
Description Field/Graph
Edges are selected by the edge strength method, which measures the rate of change from
bright to dark or dark to bright. Enter an edge strength threshold in the range from 1 to
Threshold
255. The default value is 20. As this value gets lower, the tool will find weaker, blurrier
or more gradual edges.
Polarity • Bright to Dark: Finds only the edges with their bright side towards the center of the
ROI and their dark side towards the outside of the ROI.
• Dark to Bright: Finds only the edges with their dark side towards the center of the
ROI and their bright side towards the outside of the ROI
• Bright or Dark finds all edges.
The Sample Rate sets the spacing between the invisible scan lines at the midpoint between
the inner and outer rings of the ROI. When the sample rate is raised, fewer edges will
Sample Rate
be found and they will be spaced more widely. When the sample rate is lowered, more
edge will be found. This creates a tradeoff between speed and precision. Higher sample
rates execute faster, and lower sample rates find more precision results and are capable
of detecting smaller flaws.
Search For Field
The Search For offers three ways to fit a circle to the edge points the tool finds:
• "Circle, Best Points" is the most common choice. It automatically figures which edge points make the best circle and
ignores the rest. The points that are being ignored will be shown on the image in orange. This mode is very tolerant
of noise or extra edges in the ROI, but under some circumstances it may ignore edges you wish to include.
• "Circle, All Points" finds a circle that explains all the edges as well as possible without ignoring anything. This setting
is the fastest, but it works poorly if there are any extra edges or noise within the ROI. This mode is useful if the circle
being examined is irregular or elliptical.
• "Circular Arc" finds a piece of a circle. Using this setting to find the start or end angle of an arc or bend or to measure
the angle subtended by a bend.
143 Minneapolis, MN USA Banner Engineering Corp.
PresencePLUS Software Tools 2/2010