Banner PresencePLUS P4 Series - Manual (Page 110)

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.
P/N 000000 Banner Engineering Corp. - Minneapolis, MN USA - www.bannerengineering.com
Tel: 763.544.3164
110
7/2009 PresencePLUS Software Tools