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tEnhancement of image quality is a fundamental process for a wide range of vision-based applications.Images captured under unfavorable environments are often degraded in information content, sharpnessand colorfulness. In the attempts to improve an image, the unsharp masking filter is an attractive candi-date for its computational efficiency. However, the filter is vulnerable to the over-range problem wherepixel magnitudes are driven beyond permissible ranges. This drawback is particularly noticeable if a non-adaptive procedure is used in the enhancement. Hence, an adaptive gain adjustment method is proposedhere aiming at minimizing the number of over-range pixels while maximizing the image sharpness andinformation content. In this method, colorfulness is improved via color channel stretching and contrastis enhanced by edge augmentation. Specifically, a hyperbolic-tangent function, whose scale is depen-dent on the original image intensity and detected edges, is constructed to adjust the
