Contrast restoration of foggy images through use of an onboard camera

Perception sensors (cameras, laser, radar) are being introduced into certain vehicles. These sensors have been designed to operate within a wide range of situations and conditions (weather, luminosity, etc.) with a prescribed set of variation thresholds. Effectively detecting when a given operating threshold has been surpassed constitutes a key parameter in the creation of driving assistance systems that meet required reliability levels. With this context in mind, an atmospheric visibility measurement system may be capable of quantifying the most common operating range of onboard exteroceptive sensors. In particular, foggy images suffer from poor contrast. Furthermore, this decay varies across the scene and is exponential in the depths of scene points. In this paper, we present a physics based method to restore contrast of foggy images without any a priori weather-specific prediction. Our method only uses a simple black-and-white camera mounted onboard a moving vehicle. Furthermore, we are able to estimate the meteorological visibility distance, which characterizes the weather condition.