Locally-Adaptive Image Contrast Enhancement without Noise and Ringing Artifacts

Abstract

For real-time imaging in surveillance applications, visibility of details is of primary importance to ensure customer confidence. Additional constraints are the absence of human interaction and low computational complexity. Usually, image quality is improved by enhancing contrast and sharpness. Many complex scenes require local contrast improvements that should bring details to the best possible visibility. However, local enhancement methods mainly suffer from ringing artifacts and noise over-enhancement. In this paper, we present a new multi-window real-time highfrequency enhancement scheme, in which gain is a nonlinear function of the detail energy. Our algorithm controls perceived sharpness, ringing artifacts (contrast) and noise, resulting in a good balance between visibility of details and non-disturbance of artifacts. Its advantage is that gains can be set now much higher than usual and the algorithm will reduce them only at places where it is really needed.

Local Contrast Enhancement using Local Standard Deviation

“…Sascha [16] presented another improved method in which frequency bands are separately controlled and enhanced. This is achieved by subtracting windows of two subsequent scales so that the difference between windows represents a supplementary frequency band which is added to a certain pixel neighbourhood and which is additionally enhanced by the use of the bigger kernel:…”

“…Schutte [15] introduced a multi-window extension of this technique and showed how the window sizes should be chosen. Sascha [16] implemented an improved multi-window real-time high frequency enhancement scheme based on LSD in which gain is a non-linear function of the detail energy and observed that this method is effective for the surveillance and many other applications.…”

Semi-Automatic Global Contrast Enhancement

“…A multi-window extension of the technique that the contrast gain is inversely proportional to the LSD was introduced by Schutte [14] and showed how the window sizes should be chosen. An improved multi-window real-time high frequency enhancement scheme based on LSD in which gain is a non-linear function of the detail energy was implemented by Sascha [15]. However, some enhancement methods which are using the LSD suffer from divide by zero conditions when LSD's of some pixels of the input image are having the value zero.…”

Global-Local Contrast Enhancement

“…Another method was introduced by Schutte [16] that a multi-window extension of the technique using LSD was utilized and how the window sizes should be chosen was shown. Sascha [17] implemented an improved multiwindow real-time high frequency enhancement scheme based on LSD in which gain is a non-linear function of the detail energy. Some of the enhancement-methods which are using LSD's suffer from divide by zero condition when LSD's of some pixels are having the value zero.…”