ThresholdLow Property

Applies To
Vision Objects: Blob, Contour, ImageOp, DefectFinder

Description
Sets or returns the ThresholdLow value for a Blob, DefectFinder, or ImageOp object.

Usage

VGet  Sequence.Object.ThresholdLow, var
VSet  Sequence.Object.ThresholdLow, value

Sequence

Name of a sequence or string variable containing a sequence name.

Object

Name of an object or string variable containing an object name. The object must exist in the specified sequence.

var

Integer variable that will contain the value of the property.

value

Integer value or expression for the new value of the property.

Values
0 to 254

This value must be less than the ThresholdHigh value or an error will occur.

Default: 0

Remarks
The ThresholdLow property works with the ThresholdHigh property to define the grey level regions which represent the feature (or object), the background and the edges of the image. The ThresholdLow property defines the lower bound for grey level values that are considered to be a blob. Any part of the image which falls within the grey level region between ThresholdLow and ThresholdHigh will be assigned a pixel weight of 1. (i.e. it is a blob.)

If the Polarity property is set to DarkOnLight, then grey levels between ThesholdLow and ThresholdHigh will changed to black pixels and all other pixels will be white.

If the Polarity property is set to LightOnDark, then grey levels between ThesholdLow and ThresholdHigh will changed to white pixels and all other pixels will be black.

One of the problems regarding the ThresholdLow and ThresholdHigh Properties is finding the correct values to use for each. This is where the Histogram feature of Vision Guide comes in. You can run a Histogram on an image to see the relationship between the pixel counts at various grey levels. From the Histogram dialog, you can adjust each of the threshold values and view the results.

See Also
Blob Object, Contour Object, DefectFinder Object, ImageOp Object, Polarity Property, ThresholdHigh Property