BLIND CONTRAST ENHANCEMENT ASSESSMENT BY GRADIENT RATIOING AT VISIBLE EDGES

The contrast of outdoor images acquired under adverse weath er conditions, especially foggy weather, is altered by the scattering of daylight by atmospheric particles. As a consequence, different methods have been designed to restore the contrast of these images. However, there is a l ack of methodology to assess the performances of the methods or to rate them. Unlike image quality assessment or image restoration areas, there is no easy way to have a reference image, which makes the problem not straig h forward to solve. In this paper, an approach is proposed which consists in computing the ratio between the g radient of the visible edges between the image before and after contrast restoration. In this way, an indic ator of visibility enhancement is provided based on the concept of visibility level, commonly used in lighting e ngineering. Finally, the methodology is applied to contrast enhancement assessment and to the comparison of to ne-mapping operators.

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