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@ -85,14 +85,13 @@ The goal of this paper is video action recognition.
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Given are approximately 10 seconds long videos which should be classified.
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In this paper datasets with 400 and 101 different classes are used.
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The proposed approach is tested with 1\% and 10\% of known labels of all data points.
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The used model depends on the exact usecase but in this case a 3D-ResNet50 and 3D-ResNet18 are used.
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\section{Semi-Supervised learning}\label{sec:semi-supervised-learning}
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In traditional supervised learning we have a labeled dataset.
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Each datapoint is associated with a corresponding target label.
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The goal is to fit a model to predict the labels from datapoints.
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In traditional unsupervised learning no labels are known.
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In traditional unsupervised learning there are also datapoints but no labels are known.
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The goal is to find patterns or structures in the data.
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Moreover, it can be used for clustering or downprojection.
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@ -118,8 +117,8 @@ It relies on a single model for generating pseudo-labels which can introduce err
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Incorrect pseudo-labels may effect the learning process negatively.
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Furthermore, Fixmatch uses a compareably small model for label prediction which has a limited capacity.
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This can negatively affect the learning process as well.
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There is no measure defined how certain the model is about its prediction.
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Such a measure improves overall performance by filtering noisy and unsure predictions.
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%There is no measure defined how certain the model is about its prediction.
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%Such a measure improves overall performance by filtering noisy and unsure predictions.
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Cross-Model Pseudo-Labeling tries to address all of those limitations.
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\subsection{Math of FixMatch}\label{subsec:math-of-fixmatch}
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@ -137,6 +136,12 @@ Moreover, there is the strong augmentation $\mathcal{T}_{\text{strong}}(\cdot)$
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The indicator function $\mathbbm{1}(\cdot)$ applies a principle called `confidence-based masking`.
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It retains a label only if its largest probability is above a threshold $\tau$.
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Where $p_i \coloneqq F(\mathcal{T}_{\text{weak}}(u_i))$ is a model evaluation with a weakly augmented input.
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\begin{equation}
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\label{eq:crossentropy}
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\mathcal{H}(\hat{y}_i, y_i) = -\sum_{i=1} y_i \cdot log(\hat{y}_i)
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\end{equation}
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The second part $\mathcal{H}(\cdot, \cdot)$ is a standard Cross-entropy loss function which takes two inputs, the predicted and the true label.
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$\hat{y}_i$, the obtained pseudo-label and $F(\mathcal{T}_{\text{strong}}(u_i))$, a model evaluation with strong augmentation.
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The indicator function evaluates in $0$ if the pseudo prediction is not confident and the current loss evaluation will be dropped.
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@ -145,7 +150,10 @@ Otherwise it evaluates to 1 and it will be kept and trains the model further.
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\section{Cross-Model Pseudo-Labeling}\label{sec:cross-model-pseudo-labeling}
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The newly invented approach of this paper is called Cross-Model Pseudo-Labeling (CMPL)\cite{Xu_2022_CVPR}.
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Figure~\ref{fig:cmpl-structure} visualizs the structure of CMPL\@.
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We define two different models, a smaller auxiliary model and a larger model.
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Two different models, a smaller auxiliary model and a larger model are defined.
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They provide pseudo-labels for each other.
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The two different models have a different structural bias which leads to complementary representations.
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This symetric design performs a boost in performance.
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The SG label means stop gradient.
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The loss function evaluations are fed into the opposite model as loss.
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The two models train each other.
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@ -225,6 +233,14 @@ For example:
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Those are just other approaches one can keep in mind.
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This doesn't mean they are better, in fact they performed even worse in this study.
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\section{Conclusion}\label{sec:conclusion}
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In conclusion, Cross-Model Pseudo-Labeling demonstrates the potential to significantly advance the field of semi-supervised action recognition.
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Cross-Model Pseudo-Labeling outperforms the supervised-only approach over several experiments by a multiple.
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It surpasses most of the other existing pseudo-labeling frameworks.
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Through the integration of main and auxiliary models, consistency regularization, and uncertainty estimation, CMPL offers a powerful framework for leveraging unlabeled data and improving model performance.
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It paves the way for more accurate and efficient action recognition systems.
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