Thresholdlow property – Epson 5 User Manual

Page 187

ThresholdLow Property

Applies To

Vision Objects: Blob, ImageOp

Description

Sets or returns the ThresholdLow value for a Blob 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 expression for the new value of the property.

Values

0 - 254

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

Remarks

Blob Objects:

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 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.