Dumitru Erhan

ICLR Conference 2023 Conference Paper

Phenaki: Variable Length Video Generation from Open Domain Textual Descriptions

• Ruben Villegas
• Mohammad Babaeizadeh
• Pieter-Jan Kindermans
• Hernan Moraldo
• Han Zhang 0010
• Mohammad Taghi Saffar
• Santiago Castro
• Julius Kunze

We present Phenaki, a model capable of realistic video synthesis given a sequence of textual prompts. Generating videos from text is particularly challenging due to the computational cost, limited quantities of high quality text-video data and variable length of videos. To address these issues, we introduce a new causal model for learning video representation which compresses the video to a small discrete tokens representation. This tokenizer is auto-regressive in time, which allows it to work with video representations of different length. To generate video tokens from text we are using a bidirectional masked transformer conditioned on pre-computed text tokens. The generated video tokens are subsequently de-tokenized to create the actual video. To address data issues, we demonstrate how joint training on a large corpus of image-text pairs as well as a smaller number of video-text examples can result in generalization beyond what is available in the video datasets. Compared to the previous video generation methods, Phenaki can generate arbitrary long videos conditioned on a sequence of prompts (i.e. time variable text or story) in open domain. To the best of our knowledge, this is the first time a paper studies generating videos from time variable prompts.

NeurIPS Conference 2023 Conference Paper

StoryBench: A Multifaceted Benchmark for Continuous Story Visualization

• Emanuele Bugliarello
• H. Hernan Moraldo
• Ruben Villegas
• Mohammad Babaeizadeh
• Mohammad Taghi Saffar
• Han Zhang
• Dumitru Erhan
• Vittorio Ferrari

Generating video stories from text prompts is a complex task. In addition to having high visual quality, videos need to realistically adhere to a sequence of text prompts whilst being consistent throughout the frames. Creating a benchmark for video generation requires data annotated over time, which contrasts with the single caption used often in video datasets. To fill this gap, we collect comprehensive human annotations on three existing datasets, and introduce StoryBench: a new, challenging multi-task benchmark to reliably evaluate forthcoming text-to-video models. Our benchmark includes three video generation tasks of increasing difficulty: action execution, where the next action must be generated starting from a conditioning video; story continuation, where a sequence of actions must be executed starting from a conditioning video; and story generation, where a video must be generated from only text prompts. We evaluate small yet strong text-to-video baselines, and show the benefits of training on story-like data algorithmically generated from existing video captions. Finally, we establish guidelines for human evaluation of video stories, and reaffirm the need of better automatic metrics for video generation. StoryBench aims at encouraging future research efforts in this exciting new area.

ICLR Conference 2022 Conference Paper

Information Prioritization through Empowerment in Visual Model-based RL

• Homanga Bharadhwaj
• Mohammad Babaeizadeh
• Dumitru Erhan
• Sergey Levine

Model-based reinforcement learning (RL) algorithms designed for handling complex visual observations typically learn some sort of latent state representation, either explicitly or implicitly. Standard methods of this sort do not distinguish between functionally relevant aspects of the state and irrelevant distractors, instead aiming to represent all available information equally. We propose a modified objective for model-based RL that, in combination with mutual information maximization, allows us to learn representations and dynamics for visual model-based RL without reconstruction in a way that explicitly prioritizes functionally relevant factors. The key principle behind our design is to integrate a term inspired by variational empowerment into a state-space learning model based on mutual information. This term prioritizes information that is correlated with action, thus ensuring that functionally relevant factors are captured first. Furthermore, the same empowerment term also promotes faster exploration during the RL process, especially for sparse-reward tasks where the reward signal is insufficient to drive exploration in the early stages of learning. We evaluate the approach on a suite of vision-based robot control tasks with natural video backgrounds, and show that the proposed prioritized information objective outperforms state-of-the-art model based RL approaches by an average of 20\% in terms of episodic returns at 1M environment interactions with 30\% higher sample efficiency at 100k interactions.

ICLR Conference 2020 Conference Paper

Model Based Reinforcement Learning for Atari

• Lukasz Kaiser
• Mohammad Babaeizadeh
• Piotr Milos
• Blazej Osinski
• Roy H. Campbell
• Konrad Czechowski
• Dumitru Erhan
• Chelsea Finn

Model-free reinforcement learning (RL) can be used to learn effective policies for complex tasks, such as Atari games, even from image observations. However, this typically requires very large amounts of interaction -- substantially more, in fact, than a human would need to learn the same games. How can people learn so quickly? Part of the answer may be that people can learn how the game works and predict which actions will lead to desirable outcomes. In this paper, we explore how video prediction models can similarly enable agents to solve Atari games with fewer interactions than model-free methods. We describe Simulated Policy Learning (SimPLe), a complete model-based deep RL algorithm based on video prediction models and present a comparison of several model architectures, including a novel architecture that yields the best results in our setting. Our experiments evaluate SimPLe on a range of Atari games in low data regime of 100k interactions between the agent and the environment, which corresponds to two hours of real-time play. In most games SimPLe outperforms state-of-the-art model-free algorithms, in some games by over an order of magnitude.

ICLR Conference 2020 Conference Paper

VideoFlow: A Conditional Flow-Based Model for Stochastic Video Generation

• Manoj Kumar 0019
• Mohammad Babaeizadeh
• Dumitru Erhan
• Chelsea Finn
• Sergey Levine
• Laurent Dinh
• Durk Kingma

Generative models that can model and predict sequences of future events can, in principle, learn to capture complex real-world phenomena, such as physical interactions. However, a central challenge in video prediction is that the future is highly uncertain: a sequence of past observations of events can imply many possible futures. Although a number of recent works have studied probabilistic models that can represent uncertain futures, such models are either extremely expensive computationally as in the case of pixel-level autoregressive models, or do not directly optimize the likelihood of the data. To our knowledge, our work is the first to propose multi-frame video prediction with normalizing flows, which allows for direct optimization of the data likelihood, and produces high-quality stochastic predictions. We describe an approach for modeling the latent space dynamics, and demonstrate that flow-based generative models offer a viable and competitive approach to generative modeling of video.

NeurIPS Conference 2019 Conference Paper

A Benchmark for Interpretability Methods in Deep Neural Networks

• Sara Hooker
• Dumitru Erhan
• Pieter-Jan Kindermans
• Been Kim

We propose an empirical measure of the approximate accuracy of feature importance estimates in deep neural networks. Our results across several large-scale image classification datasets show that many popular interpretability methods produce estimates of feature importance that are not better than a random designation of feature importance. Only certain ensemble based approaches---VarGrad and SmoothGrad-Squared---outperform such a random assignment of importance. The manner of ensembling remains critical, we show that some approaches do no better then the underlying method but carry a far higher computational burden.

NeurIPS Conference 2019 Conference Paper

High Fidelity Video Prediction with Large Stochastic Recurrent Neural Networks

• Ruben Villegas
• Arkanath Pathak
• Harini Kannan
• Dumitru Erhan
• Quoc Le
• Honglak Lee

Predicting future video frames is extremely challenging, as there are many factors of variation that make up the dynamics of how frames change through time. Previously proposed solutions require complex inductive biases inside network architectures with highly specialized computation, including segmentation masks, optical flow, and foreground and background separation. In this work, we question if such handcrafted architectures are necessary and instead propose a different approach: finding minimal inductive bias for video prediction while maximizing network capacity. We investigate this question by performing the first large-scale empirical study and demonstrate state-of-the-art performance by learning large models on three different datasets: one for modeling object interactions, one for modeling human motion, and one for modeling car driving.

ICML Conference 2018 Conference Paper

Hierarchical Long-term Video Prediction without Supervision

• Nevan Wichers
• Ruben Villegas
• Dumitru Erhan
• Honglak Lee

Much of recent research has been devoted to video prediction and generation, yet most of the previous works have demonstrated only limited success in generating videos on short-term horizons. The hierarchical video prediction method by Villegas et al. (2017) is an example of a state-of-the-art method for long-term video prediction, but their method is limited because it requires ground truth annotation of high-level structures (e. g. , human joint landmarks) at training time. Our network encodes the input frame, predicts a high-level encoding into the future, and then a decoder with access to the first frame produces the predicted image from the predicted encoding. The decoder also produces a mask that outlines the predicted foreground object (e. g. , person) as a by-product. Unlike Villegas et al. (2017), we develop a novel training method that jointly trains the encoder, the predictor, and the decoder together without highlevel supervision; we further improve upon this by using an adversarial loss in the feature space to train the predictor. Our method can predict about 20 seconds into the future and provides better results compared to Denton and Fergus (2018) and Finn et al. (2016) on the Human 3. 6M dataset.

NeurIPS Conference 2016 Conference Paper

Domain Separation Networks

• Konstantinos Bousmalis
• George Trigeorgis
• Nathan Silberman
• Dilip Krishnan
• Dumitru Erhan

The cost of large scale data collection and annotation often makes the application of machine learning algorithms to new tasks or datasets prohibitively expensive. One approach circumventing this cost is training models on synthetic data where annotations are provided automatically. Despite their appeal, such models often fail to generalize from synthetic to real images, necessitating domain adaptation algorithms to manipulate these models before they can be successfully applied. Existing approaches focus either on mapping representations from one domain to the other, or on learning to extract features that are invariant to the domain from which they were extracted. However, by focusing only on creating a mapping or shared representation between the two domains, they ignore the individual characteristics of each domain. We hypothesize that explicitly modeling what is unique to each domain can improve a model's ability to extract domain-invariant features. Inspired by work on private-shared component analysis, we explicitly learn to extract image representations that are partitioned into two subspaces: one component which is private to each domain and one which is shared across domains. Our model is trained to not only perform the task we care about in the source domain, but also to use the partitioned representation to reconstruct the images from both domains. Our novel architecture results in a model that outperforms the state-of-the-art on a range of unsupervised domain adaptation scenarios and additionally produces visualizations of the private and shared representations enabling interpretation of the domain adaptation process.

NeurIPS Conference 2013 Conference Paper

Deep Neural Networks for Object Detection

• Christian Szegedy
• Alexander Toshev
• Dumitru Erhan

Deep Neural Networks (DNNs) have recently shown outstanding performance on the task of whole image classification. In this paper we go one step further and address the problem of object detection -- not only classifying but also precisely localizing objects of various classes using DNNs. We present a simple and yet powerful formulation of object detection as a regression to object masks. We define a multi-scale inference procedure which is able to produce a high-resolution object detection at a low cost by a few network applications. The approach achieves state-of-the-art performance on Pascal 2007 VOC.

UAI Conference 2012 Conference Paper

Sample-efficient Nonstationary Policy Evaluation for Contextual Bandits

• Miroslav Dudík
• Dumitru Erhan
• John Langford 0001
• Lihong Li 0001

We present and prove properties of a new offline policy evaluator for an exploration learning setting which is superior to previous evaluators. In particular, it simultaneously and correctly incorporates techniques from importance weighting, doubly robust evaluation, and nonstationary policy evaluation approaches. In addition, our approach allows generating longer histories by careful control of a bias-variance tradeoff, and further decreases variance by incorporating information about randomness of the target policy. Empirical evidence from synthetic and realworld exploration learning problems shows the new evaluator successfully unifies previous approaches and uses information an order of magnitude more efficiently.

JMLR Journal 2010 Journal Article

Why Does Unsupervised Pre-training Help Deep Learning?

• Dumitru Erhan
• Yoshua Bengio
• Aaron Courville
• Pierre-Antoine Manzagol
• Pascal Vincent
• Samy Bengio

Much recent research has been devoted to learning algorithms for deep architectures such as Deep Belief Networks and stacks of auto-encoder variants, with impressive results obtained in several areas, mostly on vision and language data sets. The best results obtained on supervised learning tasks involve an unsupervised learning component, usually in an unsupervised pre-training phase. Even though these new algorithms have enabled training deep models, many questions remain as to the nature of this difficult learning problem. The main question investigated here is the following: how does unsupervised pre-training work? Answering this questions is important if learning in deep architectures is to be further improved. We propose several explanatory hypotheses and test them through extensive simulations. We empirically show the influence of pre-training with respect to architecture depth, model capacity, and number of training examples. The experiments confirm and clarify the advantage of unsupervised pre-training. The results suggest that unsupervised pre-training guides the learning towards basins of attraction of minima that support better generalization from the training data set; the evidence from these results supports a regularization explanation for the effect of pre-training. [abs] [ pdf ][ bib ] &copy JMLR 2010. ( edit, beta )

ICML Conference 2007 Conference Paper

An empirical evaluation of deep architectures on problems with many factors of variation

• Hugo Larochelle
• Dumitru Erhan
• Aaron C. Courville
• James Bergstra
• Yoshua Bengio