DSLA: Dynamic smooth label assignment for efficient anchor-free object detection

•The inconsistencies of classification and quality estimation are analyzed. Dynamic smooth label assignment is proposed to address the problems.•Interval relaxation strategy is proposed and combined with the improved centerness score. The assigned label is smoothed to a continuous value.•IoU score is dynamically calculated and coupled with the smooth label, resulting in dynamic smooth label.•DSLA is applied to popular anchor-free detectors. Comprehensive experiments are carried out on MS COCO to demonstrate the effectiveness.