Applications: Computer Vision

Jun 12, 2019



Context-Aware Zero-Shot Learning for Object Recognition Zero-Shot Learning (ZSL) aims at classifying unlabeled objects by leveraging auxiliary knowledge, such as semantic representations. A limitation of previous approaches is that only intrinsic properties of objects, e.g. their visual appearance, are taken into account while their context, e.g. the surrounding objects in the image, is ignored. Following the intuitive principle that objects tend to be found in certain contexts but not others, we propose a new and challenging approach, context-aware ZSL, that leverages semantic representations in a new way to model the conditional likelihood of an object to appear in a given context. Finally, through extensive experiments conducted on Visual Genome, we show that contextual information can substantially improve the standard ZSL approach and is robust to unbalanced classes. Band-limited Training and Inference for Convolutional Neural Networks The convolutional layers are core building blocks of neural network architecture. In general, a convolutional filter applies to the entire frequency spectrum of an input signal. We explore artificially constraining the frequency spectra of these filters, called band-limiting, during Convolutional Neural Networks (CNN) training. The band-limiting applies to both the feedforward and backpropagation steps. Through an extensive evaluation over time-series and image datasets, we observe that CNNs are resilient to this compression scheme and results suggest that CNNs learn to leverage lower-frequency components. An extensive experimental evaluation across 1D and 2D CNN training tasks illustrates: (1) band-limited training can effectively control the resource usage (GPU and memory); (2) models trained with band-limited layers retain high prediction accuracy; and (3) requires no modification to existing training algorithms or neural network architecture to use unlike other compression schemes. Learning Classifiers for Target Domain with Limited or No Labels In computer vision applications, such as domain adaptation (DA), few shot learning (FSL) and zero-shot learning (ZSL), we encounter new objects and environments, for which insufficient examples exist to allow for training “models from scratch,” and methods that adapt existing models, trained on the presented training environment(PTE), to the new scenario are required. We propose a novel visual attribute encoding method that encodes each image as a low-dimensional probability vector composed of prototypical part-type probabilities, where the prototypical parts are learnt so as to be representative to all images in PTE. We show that the resulting encoding is universal in that it serves as an input for adapting or learning classifiers for different problem contexts; with limited annotated labels in FSL; with no data and only semantic attributes in ZSL; and with unlabeled data for domain adaptation. We conduct extensive experiments on benchmark datasets and demonstrate that our method outperforms state-of-art DA, FSL or ZSL methods. Population Based Augmentation: Efficient Learning of Augmentation Policy Schedules A key challenge of leveraging data augmentation for neural network training is choosing an effective augmentation policy from a large search space of candidate operations. Properly chosen augmentation policies can lead to significant generalization improvements; however, state-of-the-art approaches such as AutoAugment are computationally infeasible to run for an ordinary user. In this paper, we introduce a new data augmentation algorithm, Population Based Augmentation (PBA), which generates augmentation policy schedules orders of magnitude faster than previous approaches. We show that PBA can match the performance of AutoAugment with orders of magnitude less overall compute. On CIFAR-10 we achieve a mean test error of 1.46%, which is slightly better than current state-of-the-art. The code for PBA is fully open source and will be made available. Anomaly Detection With Multiple-Hypotheses Predictions In one-class-learning tasks, only the normal case (foreground) can be modeled with data, whereas the variation of all possible anomalies is too erratic to be described by samples. Thus, due to the lack of representative data, the wide-spread discriminative approaches cannot cover such learning tasks, and rather generative models,which attempt to learn the input density of the foreground, are used. However, generative models suffer from a large input dimensionality (as in images) and are typically inefficient learners.We propose to learn the data distribution of the foreground more efficiently with a multi-hypotheses autoencoder. Moreover, the model is criticized by a discriminator, which prevents artificial data modes not supported by data, and which enforces diversity across hypotheses. Our multiple-hypotheses-based anomaly detection framework allows the reliable identification of out-of-distribution samples. For anomaly detection on CIFAR-10, it yields up to 3.9% points improvement over previously reported results. On a real anomaly detection task, the approach reduces the error of the baseline models from 6.8% to 1.5%. Kernel Mean Matching for Content Addressability of GANs We propose a novel procedure which adds "content-addressability" to any given unconditional implicit model e.g., a generative adversarial network (GAN). The procedure allows users to control the generative process by specifying a set (arbitrary size) of desired examples based on which similar samples are generated from the model. The proposed approach, based on kernel mean matching, is applicable to any generative models which transform latent vectors to samples, and does not require retraining of the model. Experiments on various high-dimensional image generation problems (CelebA-HQ, LSUN bedroom, bridge, tower) show that our approach is able to generate images which are consistent with the input set, while retaining the image quality of the original model. To our knowledge, this is the first work that attempts to construct, at test time, a content-addressable generative model from a trained marginal model. Neural Inverse Knitting: From Images to Manufacturing Instructions Motivated by the recent potential of mass customization brought by whole-garment knitting machines, we introduce the new problem of automatic machine instruction generation using a single image of the desired physical product, which we apply to machine knitting. We propose to tackle this problem by directly learning to synthesize regular machine instructions from real images. We create a cured dataset of real samples with their instruction counterpart and propose to use synthetic images to augment it in a novel way. We theoretically motivate our data mixing framework and show empirical results suggesting that making real images look more synthetic is beneficial in our problem setup. We will make our dataset and code publicly available for reproducibility and to motivate further research related to manufacturing and program synthesis. Making Convolutional Networks Shift-Invariant Again Modern convolutional networks are not shift-invariant, despite their convolutional nature: small shifts in the input can cause drastic changes in the output. Commonly used downsampling methods, such as max-pooling, ignore the classical sampling theorem. The well-known fix is applying a low-pass filter before downsampling. However, previous work has assumed that including such anti-aliasing filter necessarily \textit{excludes} max-pooling. We show that when integrated correctly, these operations are in fact \textit{compatible}. The technique is general and can be incorporated across other layer types, such as average-pooling and strided-convolution, and applications, such as image classification and translation. In addition, engineering the inductive bias of shift-equivariance largely removes the need for shift-based data augmentation at training time. Our results demonstrate that this classical signal processing technique has been overlooked in modern networks. Generative Modeling of Infinite Occluded Objects for Compositional Scene Representation We present a deep generative model which explicitly models object occlusions for compositional scene representation. Latent representations of objects are disentangled into location, size, shape, and appearance, and the visual scene can be generated compositionally by integrating these representations and an infinite-dimensional binary vector indicating presences of objects in the scene. By training the model to learn spatial dependences of pixels in the unsupervised setting, the number of objects, pixel-level segregation of objects, and presences of objects in overlapping regions can be estimated through inference of latent variables. Extensive experiments conducted on a series of specially designed datasets demonstrate that the proposed method outperforms two state-of-the-art methods when object occlusions exist. IMEXnet - A Forward Stable Deep Neural Network Deep convolutional neural networks have revolutionized many machine learning and computer vision tasks. Despite their enormous success, remaining key challenges limit their wider use. Pressing challenges include improving the network’s robustness to perturbations of the input images and simplifying the design of architectures that generalize. Another problem relates to the limited “field of view” of convolution operators, which means that very deep networks are required to model nonlocal relations in high-resolution image data. We introduce the IMEXnet that addresses these challenges by adapting semi-implicit methods for partial differential equations. Compared to similar explicit networks such as the residual networks (ResNets) our network is more stable. This stability has been recently shown to reduce the sensitivity to small changes in the input features and improve generalization. The implicit step connects all pixels in the images and therefore addresses the field of view problem, while being comparable to standard convolutions in terms of the number of parameters and computational complexity. We also present a new dataset for semantic segmentation and demonstrate the effectiveness of our architecture using the NYU depth dataset.



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