3 Image Enhancement 3.3.1 Histogram Equalization (HE) he formula of HE 1 If s =T(r)=(L-1)fo Pr(w)dw,then p.()=1-1,05s sL-1 Cumulative distribution function(CDF)is used as the HE transform function P,(r) P,(s) →Eq.(3.3-4)→ L-1 L-1 L-1 ab FIGURE 3.18(a)An arbitrary PDF.(b)Result of applying the transformation in Eq.(3.3-4)to all intensity levels,r.The resulting intensities,s,have a uniform PDF, independently of the form of the PDF of the r's. 第3章第9页3 Image Enhancement 第3章 第9页 3.3.1 Histogram Equalization (HE) If Cumulative distribution function (CDF) is used as the HE transform function The formula of HE ,then ,0s L-1