Physics-based approach to color image enhancement in poor visibility conditions

Abstract

Degradation of images by the atmosphere is a familiar problem. For example, when terrain is imaged from a forward-looking airborne camera, the atmosphere degradation causes a loss in both contrast and color information. Enhancement of such images is a difficult task because of the complexity in restoring both the luminance and the chrominance while maintaining good color fidelity. One particular problem is the fact that the level of contrast loss depends strongly on wavelength. A novel method is presented for the enhancement of color images. This method is based on the underlying physics of the degradation process, and the parameters required for enhancement are estimated from the image itself.

Resolution loss without imaging blur

“…Equations (35) and (38) depend on the (scene independent) system parameters fp; f ; A; B; V g. They also depend on the scene's z, β, andẼ. Figure 17 plots M haze for different parameter values.…”

“…Hence, linearity assumptions appear to lead to bounds [Eq. (38)] that are overly pessimistic. Recently, [56,57] analyzed bounds to image denoising with nonlinear filtering in terms of minimum mean square error.…”

Polarization: Beneficial for visibility enhancement?

“…1 plots Eqs. (16,18) for μ = 4.5 and two values of p. According to [9], in nature p ≤ 0.75. Therefore, higher values of p are not plotted.…”

Image Enhancement Focusing on Hazy and Non-uniform Illumination Images

“…These algorithms make use of strong assumptions or constraints to remove haze from a single image. Tan [1] maximized the contrast of a hazy image by assuming that a haze-free image has a higher contrast ratio than a hazy image. However, this method yields halo artifacts.…”