Use the Average Gray tool to determine the brightness levels of pixels found within the ROI.
Each pixel has a grayscale intensity value from 0 to 255, where 0 is black and 255 is white. The tool records the grayscale value of each pixel in an ROI and averages them. With this information, the tool can detect changes in intensity that can indicate several conditions, such as missing objects, holes, texture changes, and possible color changes.
Example applications:
• Spot-check for holes
• Check for a change in surface texture
• Check for presence/absence of a label or other objects
8.1.1 Average Gray Tool: Input Parameters
Use the Input parameters to configure how the tool analyzes an image.
Figure 54. Average Gray Tool—Input Parameters
ROI
The Region of Interest (ROI) is the user-defined group of pixels in the image that the sensor analyzes.
Figure 55. ROI Shape Selection
Resize and rotate the ROI around the feature to be analyzed. Change the shape of the ROI to a square, ellipse, or circle as needed by expanding ROI on the Parameters pane and selecting the desired shape. An ROI can be as large as the entire Field of View (FOV). The ROI automatically displays on the Image pane when a tool is added.
Masks
Add and define a mask to exclude a group of pixels from the tool analysis.
Figure 56. Masks Parameters
A mask created for a tool will not apply to any other tool in the inspection. Up to 10 masks can be added to a tool.
1. Expand Masks on the Inputs tab.
2. Click . The mask ROI automatically displays on the Image pane.
3. Select the mask shape. The mask ROI can be rectangular, elliptical, or circular.
4. Resize and rotate the mask ROI around the pixels to be excluded.
5. To delete a mask, click .
Pixel Intensity Range
Set the intensity range of pixels to analyze. Pixels with brightness values outside of this range are ignored.
Figure 57. Pixel Intensity Range Parameters The default settings of 0 to 255 allow all pixels to be included in the average calculation.
NOTE: An average grayscale result of – indicates that all pixels in the ROI have been excluded by the pixel intensity range parameter.
Image Overlays
Choose whether to display or hide the ROI or masks.
Figure 58. 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 ROI
Hides the ROI when the tool is not selected.
Hide Masks
Hides the Mask ROI when the tool is not selected.
Tool Histogram
The Tool Histogram graphically displays pixel intensity information within the current ROI.
Figure 59. 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 60. 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.
8.1.2 Average Gray Tool: Test Parameters
Use the Test parameters to configure the pass/fail conditions for the tool.
Select the parameter checkbox to enable it. Where applicable, the vertical green bar shows the current parameter information and the light gray backgrounds show the range over which a value has varied over time.
Where applicable, use the sliders or enter the minimum and maximum for the selected test parameters.
Figure 61. Average Gray Tool—Test Parameters
Average Grayscale
The grayscale value range.
Standard Deviation
The standard deviation range.
8.1.3 Average Gray Tool: Results
Tools & Results and All Results list information from the current and previous inspections.
A red box around a tool indicates that the tool failed. Status provides information about the specific failure.
All Results displays the Result, Time, Pass Count, and Fail Count information at a glance. Expand the inspection tool to see specific results for that tool.
Average Grayscale
The average grayscale value of the pixels in the ROI.
Standard Deviation
The standard deviation of the average grayscale value for the pixels in the ROI.
Execution Time
The execution time, in milliseconds, for the currently selected tool in the current inspection.
Expand Execution Time to see the historical minimum and maximum execution times up to this point for the selected tool.
Use the reset button in the Inspection Summary to reset these historical values.
Status
Status and error messages display as appropriate.
8.1.4 Using the Average Gray Tool
Follow these steps for a typical presence/absence Average Gray inspection.
NOTE: This procedure is an example only.
1. Add an Average Gray tool to the inspection.
2. Adjust the ROI to frame the desired feature.
3. Set the Test parameters to set the pass/fail criteria.
a) On the Test tab, select the Average Grayscale checkbox.
This option sets the grayscale range that must be present in the ROI so that a part passes.
b) Move the sliders or enter the minimum and maximum grayscale. Inspections outside of this range will fail. For this example, the minimum is 56.12 and the maximum is 74.83.
The green bar indicates the current grayscale and the light gray background indicates the grayscale over time since the last reset.
4. Test a complete range of good and bad samples to make sure that the sensor accepts good parts and rejects bad parts.
Figure 62. Average Gray—Pass Figure 63. Average Gray—Fail