Table 4.

Discrete probabilities $p(g_i)$ of gray levels $g_i$, with $i=0,\cdots \cdots N-1(L=8192)$, in a standardised image.

Features of intensity histogram	Definition
Mean, µ	${\sum }_{i=0}^{N-1}{g}_{i}P(g_i)$
Variance, σ2	${\sum }_{i=0}^{N-1}{(g_i-\mu )}^{2}P(g_i)$
Skewness	$\frac{{\sum }_{i=0}^{N-1}{{(g}_i-\mu )}^{3}P(g_i)}{{\sigma }^{3/2}}$
Kurtosis	$\frac{{\sum }_{i=0}^{N-1}{{(g}_i-\mu )}^{4}P(g_i)}{{\sigma }^2}$
Energy	${\sum }_{i=0}^{N-1}{P}^2(g_i)$
Entropy	${\sum }_{i=0}^{N-1}P(g_i){\mathit{log}}_{2}P(g_i)$