Mechanical Fault Diagnosis Using Color Image Recognition of Vibration Spectrogram Based on Quaternion Invariable Moment

Table 1

Texture feature statistic formula.

Characteristic statistic	Formula	Characteristic statistic	Formula
Small gradient advantage		Gray mean square error
Large gradient advantage		Gradient mean square error
Gray distribution heterogeneous		Correlation
Gradient distribution heterogeneous		Gray entropy
Energy		Gradient entropy
Average of gray		Mixed entropy
Average of gradient		Inertia
Inverse difference moment