Virtual Descriptors

In addition to the predefined descriptors Epina ImageLab supports "virtual descriptors" which are arithmetic combinations of several specified descriptors. In order to define a virtual descriptor you have to click the virtual descriptor button () and enter a simple mathematical formula based on the specified descriptors ("DCxxx"). The formula can contain the following operators:

+ (addition)
- (subtraction)
* (product)
/ division
abs (absolute value)
sqr (square)
sqrt (square root)
As an example, the following formula combines the descriptors DC001, DC004 and DC003 to give a new (virtual) descriptor: DC1*(DC4+DC3). Please note that the formula may use the descriptor identifiers without any leading zeros (i.e. "DC003" is equal to "DC3").

Hint: Please note that the formula specifying a virtual descriptor must not contain any references to other virtual descriptors; only predefined descriptors are allowed to be entered in the formula of the virtual descriptor. If the formula refers to a virtual descriptor, the virtual descriptor returns a zero value (without warning).