A Comprehensive Study of the Effect of Spatial Resolution and Color of Digital Images on Vehicle Classification

Vehicle-type classification is considered a core module for many intelligent transportation applications, such as speed monitoring, smart parking systems, and traffic analysis. In this paper, many vision-based classification techniques were presented relying only on a digital camera without the need for any extra hardware components. Dimension and color are two important characteristics of any digital image that affect the cost of the digital camera used in the image acquisition. In this paper, we present a comprehensive study of the effect of these two characteristics on the vehicle classification process in terms of accuracy and performance. We apply a set of different state-of-the-art image classifiers to the BIT-Vehicle and LabelMe data sets. Each data set is downscaled into different scales to generate a variety of spatial resolutions of each data set. Besides, we examine the effect of color by converting each color version to a gray-scale one. At last, we draw a valid conclusion in regards to the impact of these two characteristics (i.e., dimension and color) on the classification accuracy and performance of the image classification methods using more than 46 000 individual experiments. Experimental results show that there is no significant influence of both color and spatial resolutions of the vehicle images on the classification results obtained by most state-of-the-art image classification methods. However, there is a correlation between the spatial resolution and the processing time required by most image classification methods. Our findings can play an important role in saving not only money, but also time for vehicle-type classification systems.