Unsharp Masking, Countershading and Halos: Enhancements or Artifacts?

Abstract

Countershading is a common technique for local image contrast manipulations, and is widely used both in automatic settings, such as image sharpening and tonemapping, as well as under artistic control, such as in paintings and interactive image processing software. Unfortunately, countershading is a double-edged sword: while correctly chosen parameters for a given viewing condition can significantly improve the image sharpness or trick the human visual system into perceiving a higher contrast than physically present in an image, wrong parameters, or different viewing conditions can result in objectionable halo artifacts. In this paper we investigate the perception of countershading in the context of a novel mask-based contrast enhancement algorithm and analyze the circumstances under which the resulting profiles turn from image enhancement to artifact for a range of parameters and viewing conditions. Our experimental results can be modeled as a function of the width of the countershading profile. We employ this empirical function in a range of applications such as image resizing, view dependent tone mapping, and countershading analysis in photographs and works of fine art.

A Systematic Approach in Transforming Inscriptions into Modern Text –Review

“…Adaptive filters and linear unsharp masking can highlight the edges and increases the accuracy rate. In [1][2][3][4][5] authors discuss about the various binarization techniques and masking methods as initial step of preprocessing.…”

Enhancement and Segmentation of Historical Records

“…The linear Unsharp Masking (USM) technique [2] is adopted to increase the pictorial presence of an image by highlighting its regularity contents to improve the edge and detailed information in it. Nevertheless this method is easy and gives good result for many applications.…”

Style-based tone mapping for HDR images

“…UM, on the other hand, is efficient but it is not designed to avoid halos. However, it has been shown by earlier work that judicious use of UM can significantly improve image sharpness and apparent contrast [Trentacoste et al 2012]. As such, we decided to use UM for local contrast manipulations by also acknowledging that sometimes halos may be intentionally introduced by the artist to create non-photorealistic styles.…”