Image style transfer has drawn broad attention recently. However, most existing methods aim to explicitly model the transformation between different styles, and the learned model is often not generalizable to new styles. Based on the idea of style and content separation, we here propose a unified style transfer framework that consists of style encoder, content encoder, mixer and decoder. The style encoder and the content encoder are used to extract the style and content representations from the corresponding reference images. The two representations are integrated by the mixer and fed to the decoder, which generates images with the target style and content. Assuming the same encoder could be shared among different styles/contents, the style/content encoder explores a generalizable way to represent style/content information, i.e. the encoders are expected to capture the underlying representation for different styles/contents and generalize to new styles/contents. Training simultaneously with a number of styles and contents, the framework enables building one single transfer network for multiple styles and further leads to a key merit of the framework, i.e. its generalizability to new styles and contents. To evaluate the proposed framework, we apply it to both supervised and unsupervised style transfer, using character typeface transfer and neural style transfer as respective examples. For character typeface transfer, to separate the style features and content features, we leverage the conditional dependence of styles and contents given an image. For neural style transfer, we leverage the statistical information of feature maps in certain layers to represent style. Extensive experimental results have demonstrated the effectiveness and robustness of the proposed methods. Furthermore, models learned under the proposed framework are shown to be better generalizable to new styles and contents.

Neural style transfer has drawn broad attention in recent years. However, most existing methods aim to explicitly model the transformation between different styles, and the learned model is thus not generalizable to new styles. We here attempt to separate the representations for styles and contents, and propose a generalized style transfer network consisting of style encoder, content encoder, mixer and decoder. The style encoder and content encoder are used to extract the style and content factors from the style reference images and content reference images, respectively. The mixer employs a bilinear model to integrate the above two factors and finally feeds it into a decoder to generate images with target style and content. To separate the style features and content features, we leverage the conditional dependence of styles and contents given an image. During training, the encoder network learns to extract styles and contents from two sets of reference images in limited size, one with shared style and the other with shared content. This learning framework allows simultaneous style transfer among multiple styles and can be deemed as a special 'multi-task' learning scenario. The encoders are expected to capture the underlying features for different styles and contents which is generalizable to new styles and contents. For validation, we applied the proposed algorithm to the Chinese Typeface transfer problem. Extensive experiment results on character generation have demonstrated the effectiveness and robustness of our method.

Spinal metastases have a high incidence among cancer patients and may later develop to metastatic spinal cord compression (MSCC). Early detection of spinal metastases is critical for optimal treatment. The diagnosis is usually facilitated with computed tomography (CT) scans, which requires considerable efforts from well-trained radiologist. In this paper, we explore automatic spinal metastases classification based on CT images. Considering the unique characteristics of spinal CT images, a novel Deep Dual-view Network is proposed which contains two branches: a X-Y Conv Branch to extract the features for each individual cross-sectional image slice, and a Z Conv Branch to capture z-direction features from neighboring images. The features from the two branches are then fused to generate the final prediction, which imitates the doctor's way of combining cross sections with sagittal or coronal sections. Considering a tumor usually presents in multiple consecutive image slices, a smooth loss is introduced to maintain the label consistency of adjacent images. To validate the proposed approach, we collect a dataset of 316 patients with spinal metastases. Experimental results on this data set have demonstrated the effectiveness and the robustness of the proposed Deep Dual-view network.

Active learning selectively labels the most informative instances, aiming to reduce the cost of data annotation. While much effort has been devoted to active sampling functions, relatively limited attention has been paid to when the learning process should stop. In this article, we focus on the stopping criterion of active learning and propose a model stability--based criterion, that is, when a model does not change with inclusion of additional training instances. The challenge lies in how to measure the model change without labeling additional instances and training new models. Inspired by the stochastic gradient update rule, we use the gradient of the loss function at each candidate example to measure its effect on model change. We propose to stop active learning when the model change brought by any of the remaining unlabeled examples is lower than a given threshold. We apply the proposed stopping criterion to two popular classifiers: logistic regression (LR) and support vector machines (SVMs). In addition, we theoretically analyze the stability and generalization ability of the model obtained by our stopping criterion. Substantial experiments on various UCI benchmark datasets and ImageNet datasets have demonstrated that the proposed approach is highly effective.

In many classification tasks, the data distribution is imbalanced and different misclassifications involve different costs. In addition, the data collected are often lack in labels and it is expensive and tedious to label them manually. Motivated by these two problems, we propose a novel active cost-sensitive classification algorithm based on the Expected Error Reduction (EER) framework, aiming to selectively label examples which can directly optimize the expected misclassification costs. However, the native EER (N-EER) framework is inefficient and impractical due to the considerable requirement for model retraining. In this paper, we propose an efficient EER (E-EER) to overcome the inefficiency of N-EER with the application of cost-sensitive classification which is realized by incorporating the cost information into the expected loss calculation. We first present a formal formulation for EER, then the active cost-sensitive classification algorithm is derived. In order to achieve E-EER, we derive an efficient model update rule for logistic regression (LR) and cost-sensitive support vector machines (C-SVM), respectively, to avoid model retraining, which are employed as the base learners. Furthermore, we theoretically analyze the error bound of our algorithm to provide a guarantee for its generalization performance. Extensive experiments demonstrate the effectiveness and efficiency of our method.

Most existing active learning studies focus on designing sample selection algorithms. However, several fundamental problems deserve investigation to provide deep insight into active learning. In this article, we conduct an in-depth investigation on active learning for classification from the perspective of model change. We derive a general active learning framework for classification called maximum model change (MMC), which aims at querying the influential examples. The model change is quantified as the difference between the model parameters before and after training with the expanded training set. Inspired by the stochastic gradient update rule, the gradient of the loss with respect to a given candidate example is adopted to approximate the model change. This framework is applied to two popular classifiers: support vector machines and logistic regression. We analyze the convergence property of MMC and theoretically justify it. We explore the connection between MMC and uncertainty-based sampling to provide a uniform view. In addition, we discuss its potential usability to other learning models and show its applicability in a wide range of applications. We validate the MMC strategy on two kinds of benchmark datasets, the UCI repository and ImageNet, and show that it outperforms many state-of-the-art methods.