Towards Accurate One-Stage Object Detection with AP-Loss

One-stage object detectors are trained by optimizing classification-loss and localization-loss simultaneously, with the former suffering much from extreme foreground-background class imbalance issue due to the large number of anchors. This paper alleviates this issue by proposing a novel framework to replace the classification task in one-stage detectors with a ranking task, and adopting the Average-Precision loss (AP-loss) for the ranking problem. Due to its non-differentiability and non-convexity, the AP-loss cannot be optimized directly. For this purpose, we develop a novel optimization algorithm, which seamlessly combines the error-driven update scheme in perceptron learning and backpropagation algorithm in deep networks. We verify good convergence property of the proposed algorithm theoretically and empirically. Experimental results demonstrate notable performance improvement in state-of-the-art one-stage detectors based on AP-loss over different kinds of classification-losses on various benchmarks, without changing the network architectures. Code is available at https://github.com/cccorn/AP-loss.Comment: 13 pages, 7 figures, 4 tables, main paper + supplementary material, accepted to CVPR 201

Pre and Post-hoc Diagnosis and Interpretation of Malignancy from Breast DCE-MRI

We propose a new method for breast cancer screening from DCE-MRI based on a post-hoc approach that is trained using weakly annotated data (i.e., labels are available only at the image level without any lesion delineation). Our proposed post-hoc method automatically diagnosis the whole volume and, for positive cases, it localizes the malignant lesions that led to such diagnosis. Conversely, traditional approaches follow a pre-hoc approach that initially localises suspicious areas that are subsequently classified to establish the breast malignancy -- this approach is trained using strongly annotated data (i.e., it needs a delineation and classification of all lesions in an image). Another goal of this paper is to establish the advantages and disadvantages of both approaches when applied to breast screening from DCE-MRI. Relying on experiments on a breast DCE-MRI dataset that contains scans of 117 patients, our results show that the post-hoc method is more accurate for diagnosing the whole volume per patient, achieving an AUC of 0.91, while the pre-hoc method achieves an AUC of 0.81. However, the performance for localising the malignant lesions remains challenging for the post-hoc method due to the weakly labelled dataset employed during training.Comment: Submitted to Medical Image Analysi

Automatic Designs in Deep Neural Networks

To train a Deep Neural Network (DNN) that performs well for a task, many design steps are taken including data designs, model designs and loss designs. Despite that remarkable progress has been made in all these domains of designing DNNs, the unexplored design space of each component is still vast. That brings the research field of developing automated techniques to lift some heavy work from human researchers when exploring the design space. The automated designs can help human researchers to make massive or challenging design choices and reduce the expertise required from human researchers. Much effort has been made towards automated designs of DNNs, including synthetic data generation, automated data augmentation, neural architecture search and so on. Despite the huge effort, the automation of DNN designs is still far from complete. This thesis contributes in two ways: identifying new problems in the DNN design pipeline that can be solved automatically, and proposing new solutions to problems that have been explored by automated designs. The first part of this thesis presents two problems that were usually solved with manual designs but can benefit from automated designs. To tackle the problem of inefficient computation due to using a static DNN architecture for different inputs, some manual efforts have been made to use different networks for different inputs as needed, such as cascade models. We propose an automated dynamic inference framework that can cut this manual effort and automatically choose different architectures for different inputs during inference. To tackle the problem of designing differentiable loss functions for non-differentiable performance metrics, researchers usually design the loss manually for each individual task. We propose an unified loss framework that reduces the amount of manual design of losses in different tasks. The second part of this thesis discusses developing new techniques in domains where the automated design has been shown effective. In the synthetic data generation domain, we propose a novel method to automatically generate synthetic data for small-data object detection. The synthetic data generated can amend the limited annotated real data of the small-data object detection tasks, such as rare disease detection. In the architecture search domain, we propose an architecture search method customized for generative adversarial networks (GANs). GANs are commonly known unstable to train where we propose this new method that can stabilize the training of GANs in the architecture search process.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163208/1/llanlan_1.pd