# Basics

Three main categories: intensity-based, shape-based, and texture-based.## Intensity features

Mean: $$ \bar{x} = \frac{1}{MN} \sum_{x=1}^{M} \sum_{y=1}^{N} I(x,y) $$ Variance: $$ s^2 = \frac{1}{MN-1} \sum_{x=1}^{M} \sum_{y=1}^{N} (I(x,y)-\bar{x})^2 $$