A NON-LINEAR TECHNIQUE FOR THE ENHANCEMENT OF EXTREMELY NON-UNIFORM LIGHTING IMAGES

Abstract

At night scenes and under nonuniform lighting conditions, either the low intensity areas or the high intensity areas cannot be clearly seen. Various image processing techniques have been developed to recover the meaningful information under extremely low lighting conditions. Among these, the algorithms based on integrated neighborhood dependency of pixel characteristics and based on the illuminance reflectance model perform well for improving the visual quality of digital images captured under nonuniform and extremely low lighting conditions. But, they cannot perform well in extremely nonuniform lighting conditions. In this paper, anew nonlinear image enhancement algorithm, named Multiple Windowed Inverse Sigmoid (MWIS), is proposed for enhancing images captured in extremely non-uniform lighting environments. The proposed algorithm is capable of compressing bright regions and at the same time enhancing dark regions by preserving the main structure of the illuminance-reflectance modality. It is observed that the proposed algorithm yields visually optimal results on images captured under extreme lighting conditions. Also, it is envisaged that the new technique would be useful for improving the visibility of scenes of air force night time and nonuniform lighting activities.

Keywords

• Image processing
• image enhancement
• image transformation
• contrast enhancement.