“…According to the visual effect and feature parameters evaluation result we can conclude that the global gray value of the enhanced image is relatively high, so it is necessary to adjust the global gray value to improve the enhancement performance, where the paper introduces the nonlinear function for the re-enhancement process based on analysis results in paper [9,10], the transformation is expressed as (18) e2 = ( e ( , )) = { 2( e ( , )) 2 , 0 ≤ e ≤ , 1 − 2(1 − e ( , )) 2 , < e ≤ 1. In that expression, , ∈ [0, 1], is set so as the transform the turning point with the discipline so that when e ≤ , the value is going nearer to 0 and when < e , the value is going nearer to 1.…”