An
adaptive
threshold is a technique that adjusts the threshold for the 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
threshold 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 minimum and maximum limits.
Adaptive
Threshold: Bead/Blob Type
Defines
whether the bead/blob is dark against a
relatively
brighter background or bright against a darker background.
This parameter
defines
the appearance of the feature of interest. For example, if you have a dark adhesive or part on a bright
background, choose Dark.
Choosing Dark with an
adaptive
threshold type causes the tool to limit the threshold to the range
specified
by the threshold level
minimum and maximum limits. The tool
identifies
all grouped pixels below the threshold chosen as dark beads/blobs.
Choosing Bright with an
adaptive
threshold type causes the tool to limit the threshold to the range
specified
by the threshold level
minimum and maximum limits. The tool
identifies
all grouped pixels above the
specified
minimum limit and less than or equal to the
maximum limit as bright beads/blobs.
Adaptive
Threshold: Threshold
Use the sliders or enter the desired minimum and maximum possible grayscale threshold.
The green line is the current threshold value, chosen by the tool, and the sliders represent boundaries beyond which you do not want
the tool to move the threshold
settings.
Reject Level
When the Bead/Blob Type is set to Bright, use the Reject Level to narrow the range of pixel
intensities
to be considered in an
inspection.
Leaving the defaults at 0 for low and 255 for high means that the tool takes into
consideration
all grayscale levels in the ROI from 0
(black) to 255 (white).
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 FOV. The remaining 85 percent of the FOV ranges from 230 to 255 in pixel intensity.
Setting
a Reject Level of 220 allows the tool to
pay
attention
to only the bright object being inspected. Masking the bright parts of the FOV is not necessary because only pixels whose
intensity is less than the Reject Level will contribute to bright beads/blobs.
Threshold Type: Fixed
Select Fixed when the
lighting
and image content remain
relatively
constant for all
inspections.
Figure 73. Threshold Type—Fixed
Fixed Threshold: Bead/Blob Type
Defines
whether the bead/blob is dark against a
relatively
brighter background or bright against a darker background.
This parameter
defines
the appearance of the feature of interest. For example, if you have a dark adhesive or part on a bright
background, choose Dark.
Choosing Dark with a
fixed
threshold type causes the tool to
fix
the threshold at the level
specified
by the Threshold level parameter.
The tool
identifies
all grouped pixels below the
specified
threshold as dark beads/blobs.
Choosing Bright with a
fixed
threshold type causes the tool to
fix
the threshold at the Bright level
specified
by the Threshold level
parameter. The tool
identifies
all grouped pixels above the
specified
Bright threshold and less than or equal to the Reject level as bright
beads/blobs.
Fixed Threshold: Threshold
Use the slider to
define
the dark/bright
cutoff
point.
Any pixels brighter than this point
define
the bright bead while those darker than this point
define
the dark bead.
VE Series Smart Camera
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