Guidelines for Performance Assessment of Digital Imaging Systems Used in Highway Applications

Digital imaging systems installed in automated highway evaluation vehicles are generally designed on a modular basis where system components produced by various manufacturers are assembled to customize the system and fulfill the users’ needs at minimum cost. In most such cases, manufacturers’ specifications for a given system component would not be reliable with respect to the eventual performance of that system component. On the other hand, no guidelines are available for performance assessment of imaging systems as assemblies of discrete components. As such, even the refinement of optics, software, and other electronic accessories is traditionally performed based on trial and error. This paper presents objective guidelines for performance assessment of digital imaging systems. The assessment process can be accomplished through measurement of well-defined properties of images. Standard and reliable methods that can be adopted for evaluation of the previous properties are discussed first. Then, by applying the above evaluation criteria to the imaging systems of the Florida Department of Transportation’s pavement evaluation vehicle, it is shown how the causes of subquality images can be recognized and the optimum settings achieved. These findings will enable the highway personnel involved in image interpretation to better understand the properties that define the quality of images, systematically assess the capabilities and limitations of imaging systems and help formulate rational standards for specifying imaging needs. Clear-cut criteria that can identify the spatial and tonal limitations of imaging systems would also enhance the development of accurate automatic image evaluation software. Hence, the findings will facilitate the effective implementation of imaging technology by precluding the need for refinements based on trial and error.