Image Enhancement by Adaptive Power-Law Transformations

Abstract

Normally the quality of an image is improved by enhancing contrast and sharpness. The enhancement of contrast and sharpening of an image with a single function is a complex task. In real-time imaging, many complex scenes require local contrast improvements that should bring details to the best possible visibility of the image. However, local enhancement methods mainly suffer from ringing artefacts and noise over-enhancement. In this paper, we present a new adaptive spatial domain contrast and sharpness enhancement method, in which modified powerlaw transformations function is applied. Our algorithm controls perceived sharpness/smoothness, ringing artefacts (contrast) and noise, resulting in a good balance between visibility of details and non-disturbance of artefacts by
controlled parameters. Its advantage over the standard power-law transformations is to enhance sharpness smoothness and contrast with a single function by
appropriate choice of control parameters. Sharpness control parameter can be also used to smoothen the image by taking the negative value of sharpness parameter. This method can be applied both to grey scale and colour images like Gamma Correction (GC). In the case of colour images, it is applied to each channel R, G and B separately.