Table 1.

Features and representation information.

Features	Representation Information
Area	Represents the area of the spark in the image. To some extent, it reflects the amount of erosion in processing.
Energy	Represents the energy of the spark in the image. It is closely related to processing parameters such as current and voltage.
Energy density	Reflects the concentration of energy. It is the amount of energy per unit area which is closely related to the processing state of processing center.
Spark area distribution	Represents the area distribution of processing region. It is closely related to wire direction
Spark energy distribution	Represents the Energy distribution of processing region. It is closely related to wire direction.
Spark number	Represents the numbers of the spark. It reflects the morphological characteristics of spark process, such as the gathering spark generated by the discharge and the dissipating spark generated by the open circuit.
HU moment	Represents other geometric features of the spark region in the image which are invariant to rotation, translation, scale, and so on.