140 research outputs found
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
RED: Reinforced Encoder-Decoder Networks for Action Anticipation
Action anticipation aims to detect an action before it happens. Many real
world applications in robotics and surveillance are related to this predictive
capability. Current methods address this problem by first anticipating visual
representations of future frames and then categorizing the anticipated
representations to actions. However, anticipation is based on a single past
frame's representation, which ignores the history trend. Besides, it can only
anticipate a fixed future time. We propose a Reinforced Encoder-Decoder (RED)
network for action anticipation. RED takes multiple history representations as
input and learns to anticipate a sequence of future representations. One
salient aspect of RED is that a reinforcement module is adopted to provide
sequence-level supervision; the reward function is designed to encourage the
system to make correct predictions as early as possible. We test RED on
TVSeries, THUMOS-14 and TV-Human-Interaction datasets for action anticipation
and achieve state-of-the-art performance on all datasets
Cascaded Boundary Regression for Temporal Action Detection
Temporal action detection in long videos is an important problem.
State-of-the-art methods address this problem by applying action classifiers on
sliding windows. Although sliding windows may contain an identifiable portion
of the actions, they may not necessarily cover the entire action instance,
which would lead to inferior performance. We adapt a two-stage temporal action
detection pipeline with Cascaded Boundary Regression (CBR) model.
Class-agnostic proposals and specific actions are detected respectively in the
first and the second stage. CBR uses temporal coordinate regression to refine
the temporal boundaries of the sliding windows. The salient aspect of the
refinement process is that, inside each stage, the temporal boundaries are
adjusted in a cascaded way by feeding the refined windows back to the system
for further boundary refinement. We test CBR on THUMOS-14 and TVSeries, and
achieve state-of-the-art performance on both datasets. The performance gain is
especially remarkable under high IoU thresholds, e.g. map@tIoU=0.5 on THUMOS-14
is improved from 19.0% to 31.0%
Quantum Bruhat graph and tilted Richardson varieties
Quantum Bruhat graph is a weighted directed graph on a finite Weyl group
first defined by Brenti-Fomin-Postnikov. It encodes quantum Monk's rule and can
be utilized to study the -point Gromov-Witten invariants of the flag
variety. In this paper, we provide an explicit formula for the minimal weights
between any pair of permutations on the quantum Bruhat graph, and consequently
obtain an Ehresmann-like characterization for the tilted Bruhat order.
Moreover, for any ordered pair of permutations and , we define the
tilted Richardson variety , with a stratification that gives a
geometric meaning to intervals in the tilted Bruhat order. We provide a few
equivalent definitions to this new family of varieties that include Richardson
varieties, and establish some fundamental geometric properties including their
dimensions and closure relations.Comment: 28 page
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