An existing method for detecting vehicles based on computer vision segments an image region that probably includes a vehicle as a vehicle region of interest from an image captured by an imaging device, such as a video camera, according to features such as the vehicle shadow and vehicle edges.
However, in a bad environment with low contrast, such as when it is raining, snowing, or foggy, the features, such as vehicle shadow and vehicle edges, will be significantly diminished (as shown in FIG. 1a), or may even vanish (as shown in FIG. 1b). In this case, segmenting a vehicle region of interest from an image according to the vehicle shadow and vehicle edges may not be possible.