The High Resolution detector was trained with images of 800-1333px, while the mobile-friendly Low Resolution detector was trained with images of 320-640px. The reason why we provide two separate sets of pre-trained weights is because training a detector directly on the smaller images leads to a 5 mAP increase in precision comparing to passing small images to the pre-trained high-res model. Both backbones were initialized with weights fitted on ImageNet and the 3 last stages of their weights where fined-tuned during the training process.