Image contrast enhancement based on a local standard deviation model

The adaptive contrast enhancement (ACE) algorithm is a widely used image enhancement method, which needs a contrast gain to adjust high frequency components of an image. In the literature, the gain is usually inversely proportional to the local standard deviation (LSD) or is a constant. But these cause two problems in practical applications, i.e., noise overenhancement and ringing artifact. Here, a new gain is developed based on Hunt's (1976) Gaussian image model to prevent the two defects. The new gain is a nonlinear function of LSD and has the desired characteristic emphasizing the LSD regions in which details are concentrated. The authors have applied the new ACE algorithm to chest X-ray images and the simulations show the effectiveness of the proposed algorithm.