<title>Enhancement of image sequences from a forward-looking airborne camera</title>

Abstract

When an aircraft is flying in conditions of low level mist or cloud, visibility of terrain features from the cockpit may be low. However, if image enhancement techniques are applied to a sequence of images (captured at 25Hz with a cockpit-mounted camera) , the effective visibility of terrain features can be increased. The main sources of image degradation are sensor noise and the scattering and attenuation of light by haze and fog. We present a two-stage algorithm that reduces such degradation through temporal processing.The first stage involves motion-compensated temporal averaging of a set of consecutive images. The frame-toframe visual motion is calculated using navigational information, a model of the camera, and a database of terrain elevations. Since this motion is predicted independently of image content, it is unaffected by the degradation. The temporal averaging of a sequence of images produces an averaged image with a decreased level of sensor noise.The second stage reverses the loss of contrast caused by the atmosphere. The total light detected by the camera is the sum of the light scattered from the terrain and that scattered from the atmospheric particles, both of which are functions of the distance from the camera to the terrain. By considering the relationship between depth and brightness, a parametric model for the total light detected is proposed. The parameters of this model provide the means to subtract the component of light due to atmospheric scattering and to then scale the result to compensate for the attenuation of the light reflected from the terrain.The algorithm has been applied to forward-looking image sequences captured in both good and poor visibility conditions. The results show a considerable increase in effective visibility over the unprocessed images.

Automatic Target Recognition Based on Cross-Plot

“…The main sources of degradation are sensor noise, and the scattering and attenuation of electromagnetic radiation by atmospheric particles in an intervening propagation medium, resulting in fuzzy target boundaries [41] , [42] . This type of noise can affect the binary image pattern greatly.…”

Towards Fog-Free In-Vehicle Vision Systems through Contrast Restoration

“…Unfortunately, they require two differently filtered images of the same scene. Some techniques assume a flat world scene like [20]. The authors compute the extinction coefficient of fog and assume a flat world seen from a forward-looking airborne camera.…”