Windowing Histogram Analysis

To correct for non-uniform lighting or unequal illumination on the left and right sides of the face, we perform histogram fitting independently to both of these components of the image. Thus, a dark left side of the face will be brightened while a bright right side is simultaneously darkened. we perform a split or ``windowed'' histogram analysis on two components separately: the left side (l) and the right side (r) of the face. Two histograms, H_l(i) and H_r(i), generate the two mapping functions: $f_{H_l \rightarrow G}$ and $f_{H_r \rightarrow G}$ for the left window and the right window respectively. The windowing is shown in Figure .

  

Figure 4.18: Windowing to split face histogram correction for each side of the face.