Image Local Contrast Enhancement using Adaptive Non-Linear Filters

We present a locally adaptive non-linear (YENI) filter to obtain the unsharp mask of an image. The unsharp mask obtained by the YENI filter preserves the edges in the image while filtering out the local details, which correspond to mid-range frequencies in the spectrum. The enhanced image using this unsharp mask effectively prevents over/under (o/u) shooting artifacts often observed with other unsharp masking techniques. The enhanced frequency range also spans lower frequencies compared to the techniques that are based on Laplacian filter variants. This improves the visual quality of the image, as measured subjectively and objectively in the real-video experiments. Furthermore, since the YENI filter reduces to an IIR filter at each pixel location, it has a low computational complexity.