Focus for Free in Density-Based Counting
Zenglin Shi Pascal Mettes Cees G. M. Snoek
This work considers supervised learning to count from images and their
corresponding point annotations. Where density-based counting methods typically
use the point annotations only to create Gaussian-density maps, which act as
the supervision signal, the starting point of this work is that point
annotations have counting potential beyond density map generation. We introduce
two methods that repurpose the available point annotations to enhance counting
performance. The first is a counting-specific augmentation that leverages point
annotations to simulate occluded objects in both input and density images to
enhance the network's robustness to occlusions. The second method, foreground
distillation, generates foreground masks from the point annotations, from which
we train an auxiliary network on images with blacked-out backgrounds. By doing
so, it learns to extract foreground counting knowledge without interference
from the background. These methods can be seamlessly integrated with existing
counting advances and are adaptable to different loss functions. We demonstrate
complementary effects of the approaches, allowing us to achieve robust counting
results even in challenging scenarios such as background clutter, occlusion,
and varying crowd densities. Our proposed approach achieves strong counting
results on multiple datasets, including ShanghaiTech Part\_A and Part\_B,
UCF\_QNRF, JHU-Crowd++, and NWPU-Crowd.