Debidatta Dwibedi
Debidatta completed his Masters in Robotics from the Robotics Institute at CMU. His research interests lie at the intersection of machine learning, computer vision, and robotics. More information is available here.
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XIRL: Cross-embodiment Inverse Reinforcement Learning
Kevin Zakka
Andy Zeng
Pete Florence
Jeannette Bohg
CORL (2021)
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We investigate the visual cross-embodiment imitation setting, in which agents learn policies from videos of other agents (such as humans) demonstrating the same task, but with stark differences in their embodiments -- shape, actions, end-effector dynamics, etc. In this work, we demonstrate that it is possible to automatically discover and learn vision-based reward functions from cross-embodiment demonstration videos that are robust to these differences. Specifically, we present a self-supervised method for Cross-embodiment Inverse Reinforcement Learning (XIRL) that leverages temporal cycle-consistency constraints to learn deep visual embeddings that capture task progression from offline videos of demonstrations across multiple expert agents, each performing the same task differently due to embodiment differences. Prior to our work, producing rewards from self-supervised embeddings typically required alignment with a reference trajectory, which may be difficult to acquire under stark embodiment differences. We show empirically that if the embeddings are aware of task progress, simply taking the negative distance between the current state and goal state in the learned embedding space is useful as a reward for training policies with reinforcement learning. We find our learned reward function not only works for embodiments seen during training, but also generalizes to entirely new embodiments. Additionally, when transferring real-world human demonstrations to a simulated robot, we find that XIRL is more sample efficient than current best methods.
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Counting Out Time: Class Agnostic Video Periodicity in the Wild
Yusuf Aytar
Andrew Zisserman
CVPR (2020)
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The need for understanding periodic videos is pervasive. Videos of biological processes, manufacturing processes, people exercising, objects being manipulated are only a few examples where the respective fields would benefit greatly if they were able to process periodic videos automatically.
We present an approach for estimating the period with which an action is repeated in a video. The crux of the approach lies in leveraging temporal self-similarity as an intermediate representation bottleneck that allows generalization to unseen videos in the wild. We train this model with a synthetic dataset from a large unlabeled video dataset by sampling short clips of varying lengths and repeating them with different periods. However, simply training powerful video classification models on this synthetic dataset doesn't transfer to real videos. We constrain the period prediction model to use the self-similarity of temporal representations to ensure that the model generalizes to real videos with repeated actions. This combination of synthetic data and a powerful yet constrained model allows us to predict periods in a class-agnostic fashion.
Our repetition counting model substantially exceeds the state of the art performance on existing periodicity benchmarks. We also collect a new challenging dataset called Countix which is more difficult than the existing datasets, capturing difficulties in repetition counting in videos in the real-world. We present extensive experiments on this dataset and hope this encourages more research in this important problem.
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Fully convolutional deep correlation networks are currently the state of the art approaches to single object visual tracking. It is commonly assumed that these networks perform tracking by detection by matching features of the object instance with features of the scene. Strong architectural priors and conditioning on the object representation is thought to encourage this tracking strategy. Despite these efforts, we show that deep trackers often default to “tracking by saliency” detection – without relying on the object representation. This leads us to introduce an auxiliary detection task that encourages more discriminative object representations and improves tracking performance.
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We introduce a self-supervised representation learning method based on the task of temporal alignment between videos. The method trains a network using temporal cycleconsistency (TCC), a differentiable cycle-consistency loss that can be used to find correspondences across time in multiple videos. The resulting per-frame embeddings can be used to align videos by simply matching frames using nearest-neighbors in the learned embedding space.
To evaluate the power of the embeddings, we densely label the Pouring and Penn Action video datasets for action phases. We show that (i) the learned embeddings enable few-shot classification of these action phases, significantly reducing the supervised training requirements; and (ii) TCC is complementary to other methods of selfsupervised learning in videos, such as Shuffle and Learn and Time-Contrastive Networks. The embeddings are also used for a number of applications based on alignment (dense temporal correspondence) between video pairs, including transfer of metadata of synchronized modalities between videos (sounds, temporal semantic labels), synchronized playback of multiple videos, and anomaly detection. Project webpage: https://sites.google.com/view/temporal-cycle-consistency.
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Algorithms for imitation learning based on adversarial optimization, such as generative adversarial imitation learning (GAIL) and adversarial inverse reinforcement learning (AIRL), can effectively mimic demonstrated behaviours by employing both reward and reinforcement learning (RL). However, applications of
such algorithms are challenged by the inherent instability and poor sample efficiency of on-policy RL. In particular, the inadequate handling of absorbing states
in canonical implementations of RL environments causes an implicit bias in reward functions used by these algorithms. While these biases might work well
for some environments, they lead to sub-optimal behaviors in others. Moreover,
despite the ability of these algorithms to learn from a few demonstrations, they
require a prohibitively large number of the environment interactions for many
real-world applications. To address these issues, we first propose to extend the environment MDP with absorbing states which leads to task-independent, and more
importantly, unbiased rewards. Secondly, we introduce an off-policy learning algorithm, which we refer to as Discriminator-Actor-Critic. We demonstrate the
effectiveness of proper handling of absorbing states, while empirically improving
the sample efficiency by an average factor of 10. Our implementation is available
online.
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Recently, deep learning based models have pushed the state-of-the-art performance for the task of action recognition in videos. Yet, for many large-scale datasets like Kinetics and UCF101, the correct temporal order of frames doesn't seem to be essential to solving the task. We find that the temporal order matters more for the recently introduced 20BN Something-Something dataset where the task of fine-grained action recognition necessitates the model to do temporal reasoning. We show that when temporal order matters, recurrent models can significantly outperform non-recurrent models. This also provides us with an opportunity to inspect the recurrent units using qualitative approaches to get more insight into what they are encoding about actions in videos.
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Learning Actionable Representations from Visual Observations
Corey Lynch
International Conference on Intelligent Robots (IROS) (2018)
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In this work we explore a new approach for robots to teach themselves about the world simply by observing it. In particular we investigate the effectiveness of learning task-agnostic representations for continuous control tasks. We extend Time-Contrastive Networks (TCN) that learn from visual observations by embedding multiple frames jointly in the embedding space as opposed to a single frame. We show that by doing so, we are now able to encode both position and velocity attributes significantly more accurately. We test the usefulness of this self-supervised approach in a reinforcement learning setting. We show that the representations learned by agents observing themselves take random actions, or other agents perform tasks successfully, can enable the learning of continuous control policies using algorithms like Proximal Policy Optimization (PPO) using only the learned embeddings as input. We also demonstrate significant improvements on the real-world Pouring dataset with a relative error reduction of 39.4% for motion attributes and 11.1% for static attributes compared to the single-frame baseline. Video results are available at this https URL .
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Preview abstract
In this work we explore a new approach for robots to teach themselves about the world simply by observing it. In particular we investigate the effectiveness of learning task-agnostic representations for continuous control tasks. We extend Time-Contrastive Networks (TCN) that learn from visual observations by embedding multiple frames jointly in the embedding space as opposed to a single frame. We show that by doing so, we are now able to encode both position and velocity attributes significantly more accurately. We test the usefulness of this self-supervised approach in a reinforcement learning setting. We show that the representations learned by agents observing themselves take random actions, or other agents perform tasks successfully, can enable the learning of continuous control policies using algorithms like Proximal Policy Optimization (PPO) using only the learned embeddings as input.
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