Blob Analysis

Description

This Step is used to detect defects on a surface based on a depth map or an intensity image. In addition, it can extract targets from the surface.

blob analysis demo

Workflow

The process of configuring this Step is shown below.

blob analysis process

Instructions:

  1. Configure the input. Connect the ports manually or select the input(s) under Input in the parameter configuration panel.

  2. Determine whether to use feature regions.

  3. Determine whether to use reference region.

  4. Set other parameters.

  5. Select the desired output(s) under Output. For an expandable output item, click ▶ and configure the Min and Max values of the acceptable range.

  6. Run the Step and view output.

Parameter Description

Parameter Description

Use Intensity Image

Once this option is selected, the intensity image will be used together with the depth map for Blob analysis. It is not checked by default.

Use Feature Regions

Use feature region(s) to define the region where Blob analysis will be performed. If the parameter is not selected, the entire surface data will be used; if it is selected, it is necessary to set the following parameters:

  • Feature Region Mode

    This parameter is used to select whether to process the data within the feature region or outside it.

  • Feature Region

    For more information on how to set and adjust the feature region, see Feature Region.

Reference Type

Use this parameter to select the reference for Threshold Settings.

  • None: No reference plane or reference regions are used. The original depth and intensity values of the data will be used directly.

  • Reference feature region: When this option is selected, multiple feature regions can be added. The software calculates the average height or intensity of data defined by these regions as the reference value.

  • Reference plane: When this option is selected, you need to input a reference plane into the Step’s input port Reference Plane for correcting the tilt of an object. Note that correcting tilt using the reference plane may introduce shear distortion.

Threshold Settings

Refer to Threshold Settings.

Open or Close Kernel Operation

Refer to Open or Close Kernel Operation.

Use Area Filter

Once this is selected, only blobs with areas between Min Area and Max Area will be retained. It is checked by default.

  • Max Area

    The set value is the maximum possible area for retaining the blob.

  • Min Area

    The set value is the minimum possible area for retaining the blob.

Use Aspect Ratio Filter

Once this option is selected, only blobs with aspect ratios between Min Aspect Ratio and Max Aspect Ratio will be retained. It is not selected by default.

Use Circularity Filter

Once this option is selected, only blobs with circularity between Min Circularity and Max Circularity will be retained. It is not checked by default.

Use Convexity Filter

Once this option is selected, only blobs with convexity between Min Convexity and Max Convexity will be retained. It is not checked by default.

Ordering By

This parameter specifies the rules for ordering the output blobs.

Options: Position (X increasing), Position (X decreasing), Position (Y increasing), Position (Y decreasing), Area (Large to small), Area (Small to large), Row-wise, Column-wise

Row Height or Column Width

  • Set the row height when ordering blobs Row-wise. The row height starts from the blob with the smallest Y value. Blobs within the same row height are considered in the same row, and the blobs in the same row are ordered in ascending order according to their X values.

  • Set the column width when ordering blobs Column-wise. The column width starts from the blob with the smallest X value. Blobs within the same column width are considered in the same column, and the blobs in the same column are ordered in ascending order according to their Y values.

Please set the parameter values appropriately. If the set row height or column width is too small, Blobs in the same row or column may be identified as multiple rows or columns during sorting. If set too large, multiple rows or columns of Blobs may be recognized as a single row or column for sorting.

Blob Search Mode

This parameter defines the mode of searching the blobs.

  • External blobs: Ignore the internal blob of a larger blob and return only the external blob. This means that only the external blobs will be retained, while the internal blobs will be ignored.

  • External and internal blobs: Include internal blobs in larger blobs. This means that the internal blobs in addition to the external blobs will be retained in the returned result.

Merge Blob Image

This parameter determines whether to merge blobs in the output.

  • Selected: Output the blobs in an array called Blob Surface.

  • Unselected (default): Each Blob is output as individual surface data.

Max Number of Output Blobs

The maximum number of Blobs that can be output after the Step is run. It also corresponds to the upper limit of parameters such as the center point, area, and surface.

Default value: 200

Threshold Settings

Parameter Description

Threshold Filter

Determines whether data above or below the threshold are considered blobs.

  • Above: Data above the threshold will be considered blobs.

  • Below: Data below the threshold will be considered blobs.

Height Threshold

Defines the threshold above or below which data are considered blobs. The set value is the minimum or the maximum height of data points that will be considered part of a blob.

  • With Reference plane as the reference type, the height of data points to the reference plane will be calculated and compared with the Height Threshold. Data above or below the threshold are considered blobs.

  • With Reference feature region as the reference type, the average height of data points defined by the reference feature region is used as a reference value and compared with the height of each point. Data with differences above or below the Height Threshold are considered blobs.

Intensity Threshold

Defines the threshold above or below which data are considered blobs. The set value is the minimum or the maximum height of data points that will be considered part of a blob. This parameter will be displayed and then requires configuration when Use Intensity Image is selected.

Open or Close Kernel Operation

Parameter Description

Open Kernel X / Y

The X and Y kernel size, respectively, for morphological opening to remove small areas of data. Use these settings, for example, to remove bridges between areas to properly isolate them or to remove small areas entirely.

Default value: 3 px

By adjusting the X / Y values, a non-rectangle filter can be used to adapt the kernel to the kinds of unwanted data you see in the scan data.

Close Kernel X / Y

The X and Y kernel size, respectively, for morphological closing to fill in holes smaller than the specified kernel size. Use these settings, for example, to fill small areas within potential blobs that may be caused by drop-outs.

Default value: 3 px

By adjusting the X / Y values, a non-rectangle filter can be used to adapt the kernel to the kinds of holes you see in the scan data.

Output Description

Check the output item to add it to the Step, and the corresponding data will be output after the Step is run. You can select the output according to the actual measurement requirements.

If you select an expandable output item, you must expand it by clicking ▶, and then set the Min and Max values to determine the acceptable range. If the output value falls within the acceptable range, the measurement item is judged as passing (OK), or else it is judged as failing (NG).
Output Item Description

Blob Count

The number of identified blobs.

Center X of Blob(n)

The X position of the center of mass of each blob.

Center Y of Blob(n)

The Y position of the center of mass of each blob.

Mean Height of Blob(n)

The mean height of data points in each blob.

Min Height of Blob(n)

The minimum height of data points in each blob.

Max Height of Blob(n)

The maximum height of data points in each blob.

Width of Blob(n)

The width of the bounding box that encapsulates each blob, i.e., the short edge.

Length of Blob(n)

The length of the bounding box that encapsulates each blob, i.e., the long edge.

Area of Blob(n)

The area of each blob.

Center of Blob(n)

The center of mass of each blob.

Blob(n) Surface

The surface data corresponding to each blob.

Troubleshooting

  • For common errors, see Error Code List.

  • If the error code is inconsistent with the error message, please contact Technical Support for help.

CV-W2901

Error: The set height threshold is invalid.

Solution: Reset Height Threshold to make sure it works.

CV-W2902

Error: The selected reference region is invalid, or the reference plane cannot be used in the grayscale mode.

Possible causes:

  • Reference Type is not configured properly.

  • After selecting the “Use Intensity Image” option, the reference plane cannot be used.

Solution:

  • Configure Reference Type correctly.

  • Unselect the “Use Intensity Image” option, or choose another reference type after selecting the option.

CV-W2903

Error: The input reference plane is invalid.

Possible cause: The parameters related to the reference plane are not set properly.

Solution: Check the parameters related to the reference plane and ensure that the input reference plane is valid.

CV-W2904

Error: The “Kernel Size” value of the selected filter should exceed 0.

Possible cause: The “Kernel Size” value is less than or equal to 0.

Solution: Adjust the “Kernel Size” to ensure that it is greater than 0.

CV-W2905

Error: No blobs detected.

Possible causes:

  • No blob exists within the feature region.

  • Height Threshold is not set properly.

Solution:

  • Check and adjust the feature region to ensure that blobs are present in it.

  • Reset Height Threshold to ensure that the number of blobs above or below (as configured) the threshold is not 0.

CV-W2906

Error: The “Row Height or Column Width” value is outside of the valid range.

Possible cause: The parameter value is less than or equal to 0.

Solution: Adjust the parameter value to ensure it is greater than 0.

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