70 research outputs found
Localizing Actions from Video Labels and Pseudo-Annotations
The goal of this paper is to determine the spatio-temporal location of
actions in video. Where training from hard to obtain box annotations is the
norm, we propose an intuitive and effective algorithm that localizes actions
from their class label only. We are inspired by recent work showing that
unsupervised action proposals selected with human point-supervision perform as
well as using expensive box annotations. Rather than asking users to provide
point supervision, we propose fully automatic visual cues that replace manual
point annotations. We call the cues pseudo-annotations, introduce five of them,
and propose a correlation metric for automatically selecting and combining
them. Thorough evaluation on challenging action localization datasets shows
that we reach results comparable to results with full box supervision. We also
show that pseudo-annotations can be leveraged during testing to improve weakly-
and strongly-supervised localizers.Comment: BMV
Spatial-Aware Object Embeddings for Zero-Shot Localization and Classification of Actions
We aim for zero-shot localization and classification of human actions in
video. Where traditional approaches rely on global attribute or object
classification scores for their zero-shot knowledge transfer, our main
contribution is a spatial-aware object embedding. To arrive at spatial
awareness, we build our embedding on top of freely available actor and object
detectors. Relevance of objects is determined in a word embedding space and
further enforced with estimated spatial preferences. Besides local object
awareness, we also embed global object awareness into our embedding to maximize
actor and object interaction. Finally, we exploit the object positions and
sizes in the spatial-aware embedding to demonstrate a new spatio-temporal
action retrieval scenario with composite queries. Action localization and
classification experiments on four contemporary action video datasets support
our proposal. Apart from state-of-the-art results in the zero-shot localization
and classification settings, our spatial-aware embedding is even competitive
with recent supervised action localization alternatives.Comment: ICC
Spatio-Temporal Action Detection with Cascade Proposal and Location Anticipation
In this work, we address the problem of spatio-temporal action detection in
temporally untrimmed videos. It is an important and challenging task as finding
accurate human actions in both temporal and spatial space is important for
analyzing large-scale video data. To tackle this problem, we propose a cascade
proposal and location anticipation (CPLA) model for frame-level action
detection. There are several salient points of our model: (1) a cascade region
proposal network (casRPN) is adopted for action proposal generation and shows
better localization accuracy compared with single region proposal network
(RPN); (2) action spatio-temporal consistencies are exploited via a location
anticipation network (LAN) and thus frame-level action detection is not
conducted independently. Frame-level detections are then linked by solving an
linking score maximization problem, and temporally trimmed into spatio-temporal
action tubes. We demonstrate the effectiveness of our model on the challenging
UCF101 and LIRIS-HARL datasets, both achieving state-of-the-art performance.Comment: Accepted at BMVC 2017 (oral
Action Recognition from Single Timestamp Supervision in Untrimmed Videos
Recognising actions in videos relies on labelled supervision during training,
typically the start and end times of each action instance. This supervision is
not only subjective, but also expensive to acquire. Weak video-level
supervision has been successfully exploited for recognition in untrimmed
videos, however it is challenged when the number of different actions in
training videos increases. We propose a method that is supervised by single
timestamps located around each action instance, in untrimmed videos. We replace
expensive action bounds with sampling distributions initialised from these
timestamps. We then use the classifier's response to iteratively update the
sampling distributions. We demonstrate that these distributions converge to the
location and extent of discriminative action segments. We evaluate our method
on three datasets for fine-grained recognition, with increasing number of
different actions per video, and show that single timestamps offer a reasonable
compromise between recognition performance and labelling effort, performing
comparably to full temporal supervision. Our update method improves top-1 test
accuracy by up to 5.4%. across the evaluated datasets.Comment: CVPR 201
Vision-based Detection of Acoustic Timed Events: a Case Study on Clarinet Note Onsets
Acoustic events often have a visual counterpart. Knowledge of visual
information can aid the understanding of complex auditory scenes, even when
only a stereo mixdown is available in the audio domain, \eg identifying which
musicians are playing in large musical ensembles. In this paper, we consider a
vision-based approach to note onset detection. As a case study we focus on
challenging, real-world clarinetist videos and carry out preliminary
experiments on a 3D convolutional neural network based on multiple streams and
purposely avoiding temporal pooling. We release an audiovisual dataset with 4.5
hours of clarinetist videos together with cleaned annotations which include
about 36,000 onsets and the coordinates for a number of salient points and
regions of interest. By performing several training trials on our dataset, we
learned that the problem is challenging. We found that the CNN model is highly
sensitive to the optimization algorithm and hyper-parameters, and that treating
the problem as binary classification may prevent the joint optimization of
precision and recall. To encourage further research, we publicly share our
dataset, annotations and all models and detail which issues we came across
during our preliminary experiments.Comment: Proceedings of the First International Conference on Deep Learning
and Music, Anchorage, US, May, 2017 (arXiv:1706.08675v1 [cs.NE]
Learning Intelligent Dialogs for Bounding Box Annotation
We introduce Intelligent Annotation Dialogs for bounding box annotation. We
train an agent to automatically choose a sequence of actions for a human
annotator to produce a bounding box in a minimal amount of time. Specifically,
we consider two actions: box verification, where the annotator verifies a box
generated by an object detector, and manual box drawing. We explore two kinds
of agents, one based on predicting the probability that a box will be
positively verified, and the other based on reinforcement learning. We
demonstrate that (1) our agents are able to learn efficient annotation
strategies in several scenarios, automatically adapting to the image
difficulty, the desired quality of the boxes, and the detector strength; (2) in
all scenarios the resulting annotation dialogs speed up annotation compared to
manual box drawing alone and box verification alone, while also outperforming
any fixed combination of verification and drawing in most scenarios; (3) in a
realistic scenario where the detector is iteratively re-trained, our agents
evolve a series of strategies that reflect the shifting trade-off between
verification and drawing as the detector grows stronger.Comment: This paper appeared at CVPR 201
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