Banner PresencePLUS P4 COLOR Series - Manual (Page 115)

Adaptive thresholding is a technique that is used to adjust the threshold for the BLOB tool based upon lighting changes
and image content within the ROI. It performs best if used with bi-modal images, which have a clear contrast in the
ROI. Adaptive thresholding chooses the current threshold value by converging to a value based on the average value
of the pixels above and below the previous threshold value; it will not move the value of the threshold above or below
the upper or lower limits.
Low Limit: Enter a gray scale value in this field, and the tool will not allow the Adaptive threshold to go below this
value.
Upper Limit: Enter a gray scale value in this field, and the tool will not allow the Adaptive threshold to go above this
value.
Reject Level: The Reject Level field is for bright Blobs only, and is used to narrow the range of pixel intensities to
consider in an inspection. Leaving the defaults at 0 for low and 255 for high will result in the tool taking into
consideration all gray scale levels in the ROI from 0 (black) to 255 (white). Note that the Reject Level field is visible
only when Bright bead type is selected.
Reject Level Example
Consider setting up an inspection for a relatively bright object that ranges from 180 to 200 in pixel intensity and takes
up 15 percent of the Field of View; yet, the remaining 85 percent of the Field of View ranges from 230 to 255 in pixel
intensity. Setting a Reject Level of 220 will allow the tool to “pay attention” to only the bright object being inspected.
Further, masking the bright parts of the Field of View will not be necessary as only pixels whose intensity is less than
the Reject Level will contribute to bright Blobs. Note that rejected pixels are colored orange in the histogram.
Blob Type
• Choose Dark if the part is darker than the background.
• Choosing Dark with a Fixed threshold will cause the tool to fix the threshold at the level specified in the Threshold
level field. The tool will choose as dark Blobs all grouped pixels below the specified threshold.
• Choosing Dark with an Adaptive threshold type will cause the tool to limit the threshold to the range specified in
the Threshold level Lower and Upper Limit fields. The tool will choose as dark Blobs all grouped pixels below the
threshold chosen.
• Choose Bright if the part is lighter than the background.
• Choosing Bright with a Fixed threshold type will cause the tool to fix the threshold at the Bright level specified in
the Threshold level field. The tool will choose as bright Blobs all grouped pixels above the specified Bright threshold
and less than or equal to the Reject level. Note: Pixels in the ROI which are brighter than the specified Reject level
will turn orange in the Image window and be ignored during inspection.
• Choosing Bright with an Adaptive threshold type will cause the tool to limit the threshold to the range specified in
the Threshold level Lower and Upper Limit fields. The tool will choose as bright Blobs all grouped pixels above
the specified Lower Limit and less than or equal to the Upper Limit. Note: Pixels in the ROI which are brighter
than the specified Reject level will turn orange in the Image window and be ignored during inspection.
Blob Find Tool Input Tab Results
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PresencePLUS Software Tools 2/2010