An improved unsharp masking method for borehole image enhancement

The motive of borehole image enhancement is to highlight the details of geological objects. In this paper, an improved unsharp masking algorithm is presented to enhance the contrast of borehole images. This method introduces the local histogram equalization into the nonlinear unsharp masking scheme. The unsharp masking approache is simple and effective for contrast enhancement of high-frequency components, but it suffers from two main drawbacks: (1) The resence of the linear highpass filter makes the system extremely sensitive to the noises. (2) It enhances high-contrast areas much more than areas that do not exhibit high image dynamics. The nonlinear unsharp masking algorithm can adaptively enhance local details for different contrast areas. The local histogram equalization provides high-frequency components of images, which is insensitive to the noises. The proposed method is compared with other techniques in the paper and the experimental result demonstrates that the proposed approach can enhance the fine details of borehole image effectively. It not only reduces the noise influence of the unsharp masking technique, but also enhances the local details of geological objects in borehole images.