A new class of nonlinear filters for image enhancement

Abstract

Two new types of very simple two-dimensional nonlinear filters are introduced and applied to image contrast enhancement. The first type is based on a generalization of the so-called Teager's algorithm [ 11. A theoretical analysis has shown that this type of nonlinear filter works like a local-meanweighted highpass filter. Based on this analysis, a second type of nonlinear filter has been developed which works like a localmean weighted bandpass filter. The proposed image contrast enhancement technique is based on combining the original image with its filtered version obtained using one of the two nonlinear filters. Very high quality enhancement has been achieved for natural images.

<title>Image enhancement by nonlinear extrapolation in frequency space</title>

“…A major difference between the two nonlinearities is that the phase of the edges is preserved in our algorithm, following the scale-space formalism. The procedure outlined in [7], however, has the effect of shifting the phase toward the brighter region. Computationally, the main difference between the approaches is in the chosen nonlinearities.…”

“…A different nonlinear filter for image enhancement has been proposed in [7]. The filter behaves like a local-mean-weighted highpass filter.…”

“…This is part of the pyramid generation. In [7], the filtering is biased either in the vertical and horizontal directions or along the diagonal directions-with the latter chosen as giving better performance. A visual-based comparison between the two nonlinear filter performances, was presented in [4] demonstrating slight differences, with less aliasing effects evident using the isotropic Laplacian filter.…”

Low-quality image enhancement using visual attention

“…Polynomial filters are frequently used to replace the high-pass filter in the unsharp masking scheme. 1,2 In Ref. 3, the proposed structure is similar to the conventional unsharp masking, except that the enhancement is allowed only in the direction of the maximal change, and the enhancement parameter is computed as a nonlinear function of the rate of change.…”

Teager energy based blood cell segmentation

“…As a result, the edges, which are uncorrelated are expected to stand out separately. TEO can be easily extended to 2 dimensions e.g.,.Xyype IB filter suggested by Mitra [3] which is obtained by applying the filtering operation along the diagonal directions.…”