8.5 Edge Tool
8.5.1 Edge Tool: Input Parameters
ROI Width
The ROI width increases in increments of 4 pixels (for example, 1, 5, 9, 13, ...) up to the total FOV size.
Note that:
• Narrow ROIs execute faster but could miss the edge
• Wide ROIs are more consistent but don't execute as fast
• A wide ROI provides an average value/location, which results in improved repeatability
• The ROI must be 13 pixels or wider to calculate the rotation of a part (Locate tool only) Sample Rate
The sample rate sets the number of samples per pixels (one sample per pixel, two samples per pixel, etc.). The sample rate determines the sub-pixel resolution, which increases the resolution of the tool, and increases the inspection time.
Figure 128. 1 px Wide ROI Figure 129. 13 px Wide ROI
Threshold
The Threshold parameter marks the grayscale transition point.
The tool marks the edge where the pixel intensity crosses the threshold level. From the Threshold Type list, select one of the following:
• Absolute
• Relative (default)
• Edge Strength
Threshold Type: Absolute
Finds an edge at a specific grayscale level.
Figure 130. Absolute Threshold Parameters
While Absolute threshold is less likely to find a false edge than Relative threshold, it may miss edges if the light level changes between inspections.
Absolute Threshold: Value
Enter a specific grayscale value from 0 to 255.
Edge Polarity
Edge Polarity defines the type of edges the tool will find.
• Dark to Bright—Finds edges where pixel intensities start below the threshold value and cross above the threshold value
• Bright to Dark—Finds edges where pixel intensities start above the threshold value and cross below the threshold value
• Bright or Dark—Finds any edge
Absolute Threshold: Edge Profile Graph
Figure 131. Absolute Threshold—Edge Profile Graph
For absolute threshold, the x axis is the length of the ROI. The y axis is the actual grayscale value from 0 to 255. The light blue line shows the absolute pixel intensity. The horizontal gray threshold line moves up or down with the threshold value.
Point to a location on the graph—the corresponding location is the yellow line on the tool ROI displayed on the image.
Threshold Type: Relative
Finds an edge at a relative pixel intensity. This is the default threshold setting.
Figure 132. Relative Threshold Parameters
The brightest grayscale level found along the ROI is 100% and the darkest is 0%. While Relative threshold is more tolerant of light fluctuations between inspections than other transition types, it may find false edges.
Relative Threshold: Percent
Choose the percentage value at which the edge should be marked.
Edge Polarity
Edge Polarity defines the type of edges the tool will find.
• Dark to Bright—Finds edges where pixel intensities start below the threshold value and cross above the threshold value
• Bright to Dark—Finds edges where pixel intensities start above the threshold value and cross below the threshold value
• Bright or Dark—Finds any edge
Relative Threshold: Edge Profile Graph
Figure 133. Relative Threshold—Edge Profile Graph
For relative threshold, the x axis is the length of the ROI. The y axis is the pixel intensity along the ROI, with 0% as the darkest pixel in the ROI and 100% as the lightest pixel in the ROI. The light blue line shows the percentage pixel intensity relative to the horizontal gray threshold line. The threshold line moves up or down with the percent value.
NOTE: Because the pixel intensity is relative to what is seen in the ROI, this does not necessarily mean that 0% = pure black or that 100% = pure white.
Point to a location on the graph—the corresponding location is the yellow line on the tool ROI displayed on the image.
Threshold Type: Edge Strength
Measures the rate of change of grayscale values and needs sharply-defined transitions to find edges.
Figure 134. Edge Strength Threshold Parameters
Edge strength ignores gradual changes in light levels across the tool better than other threshold types and it filters out weak or gradual edges.
Edge Strength Threshold: Edge Strength Enter an edge strength value from 1 to 255.
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 255. The default value is 20. As this value is reduced, the tool finds weak, blurry, or more gradual edges.
Edge Polarity
Edge Polarity defines the type of edges the tool will find.
• Dark to Bright—Finds edges where pixel intensities start below the threshold value and cross above the threshold value
• Bright to Dark—Finds edges where pixel intensities start above the threshold value and cross below the threshold value
• Bright or Dark—Finds any edge
Edge Strength Threshold: Edge Profile Graph
Figure 135. Edge Strength Threshold—Edge Profile Graph
For edge strength threshold, the x axis is the length of the ROI. The y axis has two measurements. The first is the light blue axis. It represents Edge Strength, a measure of the rate of change of pixel grayscale values. The second is the dark gray axis. It represents Edge Profile, which gives the absolute grayscale level across the tool ROI. The blue line is the rate of change of the grayscale value along the ROI. The two horizontal gray lines are the edge strength threshold plus and minus.
Point to a location on the graph—the corresponding location is the yellow line on the tool ROI displayed on the image.
Filters
Set filters for tool analysis.
Figure 136. Edge Tool Filters Smoothing
Runs a rolling average along the ROI length. It filters out sharp changes in the edge profile.
NOTE: A high filter number may miss the edge of a narrow line.
Minimum Edge Width
Filters out small spike-of-intensity changes, and narrow dark or bright bands. It determines the distance before and after an edge that must be free from additional transitions or the end of the ROI before the edge is recognized as valid.
NOTE: A high filter number may miss the edge of a narrow line.
Edge Profile
The Edge Profile graph changes depending on which threshold type is selected. Refer to the Threshold section and the specific threshold types for details on the Edge Profile graph.
Image Overlays
Chose whether to display or hide the annotations or the ROI when this tool is not selected.
Figure 137. Image Overlays—Default
These options override the ROI view buttons on the Image Pane Parameters when no tool is selected. When a specific tool is selected, the ROI information is shown.
Hide Annotations
Hides the annotations on the live image for the tool, even when the tool is selected.
Figure 138. Show Edge Tool Annotations Figure 139. Hide Edge Tool Annotations
Hide ROI
Hides the ROI when the tool is not selected.
Tool Histogram
The Tool Histogram graphically displays pixel intensity information within the current ROI.
Figure 140. Example Histogram
Select the Tool Histogram checkbox to enable the histogram. The default is enabled. Expand the Tool Histogram parameter to view the histogram.
The histogram is a display of the grayscale values on the x axis and the number of pixels on the y axis. The histogram displays the amount of pixels for each grayscale value. The graph displays information for all grayscale values (0 to 255).
Move the pointer anywhere over the histogram to view specific information. The information updates as the position of the pointer changes.
Inspection Pass/Fail
Select the Contribute to Inspection Pass/Fail check box (default) if the tool will influence the Pass/Fail status of the inspection.
Figure 141. Inspection Pass/Fail
The Pass/Fail contribution influences the following:
• Discrete output Pass
• Discrete output Fail
• Pass/Fail results counter
• Pass (Green) and Fail (red) LEDs on the Sensor
Select this checkbox if the overall Pass/Fail status of the inspection is dependent on the current tool.