Current state-of-the-art object objectors are fine-tuned from the off-the-shelf networks pretrained on large-scale classification dataset ImageNet, which incurs some additional problems: 1) The classification and detection have different degrees of sensitivity to translation, resulting in the learning objective bias; 2) The architecture is limited by the classification network, leading to the inconvenience of modification. To cope with these problems, training detectors from scratch is a feasible solution. However, the detectors trained from scratch generally perform worse than the pretrained ones, even suffer from the convergence issue in training. In this paper, we explore to train object detectors from scratch robustly. By analysing the previous work on optimization landscape, we find that one of the overlooked points in current trained-from-scratch detector is the BatchNorm. Resorting to the stable and predictable gradient brought by BatchNorm, detectors can be trained from scratch stably while keeping the favourable performance independent to the network architecture. Taking this advantage, we are able to explore various types of networks for object detection, without suffering from the poor convergence. By extensive experiments and analyses on downsampling factor, we propose the Root-ResNet backbone network, which makes full use of the information from original images. Our ScratchDet achieves the state-of-the-art accuracy on PASCAL VOC 2007, 2012 and MS COCO among all the train-from-scratch detectors and even performs better than several one-stage pretrained methods. Codes will be made publicly available at this https URL.
We present Deeply Supervised Object Detector (DSOD), a framework that can learn object detectors from scratch. State-of-the-art object objectors rely heavily on the off-the-shelf networks pre-trained on large-scale classification datasets like ImageNet, which incurs learning bias due to the difference on both the loss functions and the category distributions between classification and detection tasks. Model fine-tuning for the detection task could alleviate this bias to some extent but not fundamentally. Besides, transferring pre-trained models from classification to detection between discrepant domains is even more difficult (e.g. RGB to depth images). A better solution to tackle these two critical problems is to train object detectors from scratch, which motivates our proposed DSOD. Previous efforts in this direction mostly failed due to much more complicated loss functions and limited training data in object detection. In DSOD, we contribute a set of design principles for training object detectors from scratch. One of the key findings is that deep supervision, enabled by dense layer-wise connections, plays a critical role in learning a good detector. Combining with several other principles, we develop DSOD following the single-shot detection (SSD) framework. Experiments on PASCAL VOC 2007, 2012 and MS COCO datasets demonstrate that DSOD can achieve better results than the state-of-the-art solutions with much more compact models. For instance, DSOD outperforms SSD on all three benchmarks with real-time detection speed, while requires only 1 2 parameters to SSD and 1 10 parameters to Faster RCNN. Our code and models are available at: this https URL . In this paper, we propose gated recurrent feature pyramid for the problem of learning object detection from scratch. Our approach is motivated by the recent work of deeply supervised object detector (DSOD), but explores new network architecture that dynamically adjusts the supervision intensities of intermediate layers for various scales in object detection. The benefits of the proposed method are two-fold: First, we propose a recurrent feature-pyramid structure to squeeze rich spatial and semantic features into a single prediction layer that further reduces the number of parameters to learn (DSOD need learn 1 2, but our method need only 1 3). Thus our new model is more fit for learning from scratch, and can converge faster than DSOD (using only 50 of iterations). Second, we introduce a novel gate-controlled prediction strategy to adaptively enhance or attenuate supervision at different scales based on the input object size. As a result, our model is more suitable for detecting small objects. To the best of our knowledge, our study is the best performed model of learning object detection from scratch. Our method in the PASCAL VOC 2012 comp3 leaderboard (which compares object detectors that are trained only with PASCAL VOC data) demonstrates a significant performance jump, from previous 64 to our 77 (VOC 07++12) and 72.5 (VOC 12). We also evaluate the performance of our method on PASCAL VOC 2007, 2012 and MS COCO datasets, and find that the accuracy of our learning from scratch method can even beat a lot of the state-of-the-art detection methods which use pre-trained models from ImageNet. Code is available at: this https URL .