Filter Variables

The Filter Variables module provides a way to filter a variable's value over time in order to remove noise generated in a given image. For example, when tracking a color object using the Center of Gravity module the actual COG_X and COG_Y reported will tend to vibrate somewhat even in a stable image due to pixel noise. Using the Filter Variable module you can specify that the current value is in fact the current value plus a combination from previous values of that variable. This allows you to smooth the current value based on previous values to provide a more stable representation of what the current value is.

Interface

Instructions

1. Variables to Process - Select which variables you wish to filter using the provided "Available Variables" listbox. Either double click on a variable of select a variable and click on the appropriate yellow arrow to move the variable into the Process variables listbox. As soon as the variable shows in the Process Variables listbox it will be filtered. Note that if you wish to preserve the current unfiltered value you will need to create a copy of the variable. See the Set Variable module to do so.

2. Method - Once your variables are selected you will need to select which filtering method to apply to the variable.

• Mean - Calculates the mean of the last X and current variable values and substitutes the current value for that result.

• Median - Calculates the middle value of the last X and current variable value from a sorted list of the past values and substitutes the current value for that result.

• Mode - Determines the most frequent value of the last X values and substitutes the current value for that result. If no values occur more than once then the Median is used instead.

• Bilateral - Calculates the bilateral value of the last X values and substitutes the current value for that result. Note the Bilateral threshold is used during this calculation.

• Max - Substitutes the current value for the maximum value seen in the last X and current values.

• Min - Substitutes the current value for the minimum value seen in the last X and current values.

• Midpoint - Substitutes the current value for the midpoint value seen in the last X and current values. The midpoint value is calculated by determining the average of the max and min value of the last X values.

• Peak - Determines the value of the last peak seen in the last X values. A peak is defined as an increase followed by a decrease in value around a single point. Due to this the current value can NEVER be a peak as the definition requires at least one previous and one next value around a point to determine if it is a peak or not.

• Valley - Opposite of a peak, a valley is defined as a decrease followed by an increase in value around a single point. Again, the current value cannot be defined as a valley as the next value is not yet known.

• Change - A combination of a peak or valley that indicates the last value when either a peak or a valley was detected.

• Line - Calculates a line that best fits the last X values and uses that equation to determine what the current value would be if placed on that line.

• Delta - Calculates the difference between the current value and the average of the last X values.

See Also

Set Variable
Chart Variables

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