Vehicle Detection based on Positive Samples Selection with Low Threshold

Abstract

Vehicle detection is a challenging task in computer vision. Since the differences among different vehicle shapes are small and not easy to recognize, the common object detection models usually do not work well for vehicle recognition. To select positive samples, the existing anchor-based detection methods usually use high-quality anchor boxes which are very close to the shapes of the vehicles. Such methods often make the prediction strongly dependent on high-quality anchor boxes. At present, the ATSS (Adaptive Training Sample Selection) method has also been used to select high-quality anchor boxes. The main purpose of this method is to automatically set the shapes of the anchor boxes according to the training datasets. However, for vehicle detection, the shapes of the vehicles are usually similar while the scales of the vehicles are quite different, which may influence the performance of the ATSS based vehicle detection. To solve the above problems, we propose a vehicle detection model PSLTNet (Positives Selection with Low Threshold Network). To reduce the prediction instability due to relying on high-quality anchor boxes, PSLTNet applies the positive samples selection with low threshold to enhance the prediction ability for different quality anchor boxes. To improve the identification ability of different vehicle types, PSLTNet adopts a pyramid structure and cascades dilated convolutions at each level. In addition, in order to make the bounding box regression loss be independent of scales, PSLTNet uses GIOU (Generalized Intersection Over Union) to supervise the position regression task of candidate bounding boxes. Finally, to reduce the loss of a large number of simple negatives, PSLTNet uses Focal Loss to supervise the classification task of the background candidate bounding boxes. The Experimental results upon the BIT-Vehicle dataset show that the proposed method can obtain better performance than that of the existing methods.