11,893 research outputs found
Automatically Discovering and Learning New Visual Categories with Ranking Statistics
We tackle the problem of discovering novel classes in an image collection
given labelled examples of other classes. This setting is similar to
semi-supervised learning, but significantly harder because there are no
labelled examples for the new classes. The challenge, then, is to leverage the
information contained in the labelled images in order to learn a
general-purpose clustering model and use the latter to identify the new classes
in the unlabelled data. In this work we address this problem by combining three
ideas: (1) we suggest that the common approach of bootstrapping an image
representation using the labeled data only introduces an unwanted bias, and
that this can be avoided by using self-supervised learning to train the
representation from scratch on the union of labelled and unlabelled data; (2)
we use rank statistics to transfer the model's knowledge of the labelled
classes to the problem of clustering the unlabelled images; and, (3) we train
the data representation by optimizing a joint objective function on the
labelled and unlabelled subsets of the data, improving both the supervised
classification of the labelled data, and the clustering of the unlabelled data.
We evaluate our approach on standard classification benchmarks and outperform
current methods for novel category discovery by a significant margin.Comment: ICLR 2020, code: http://www.robots.ox.ac.uk/~vgg/research/auto_nove
Semi-Supervised Learning with Scarce Annotations
While semi-supervised learning (SSL) algorithms provide an efficient way to
make use of both labelled and unlabelled data, they generally struggle when the
number of annotated samples is very small. In this work, we consider the
problem of SSL multi-class classification with very few labelled instances. We
introduce two key ideas. The first is a simple but effective one: we leverage
the power of transfer learning among different tasks and self-supervision to
initialize a good representation of the data without making use of any label.
The second idea is a new algorithm for SSL that can exploit well such a
pre-trained representation.
The algorithm works by alternating two phases, one fitting the labelled
points and one fitting the unlabelled ones, with carefully-controlled
information flow between them. The benefits are greatly reducing overfitting of
the labelled data and avoiding issue with balancing labelled and unlabelled
losses during training. We show empirically that this method can successfully
train competitive models with as few as 10 labelled data points per class. More
in general, we show that the idea of bootstrapping features using
self-supervised learning always improves SSL on standard benchmarks. We show
that our algorithm works increasingly well compared to other methods when
refining from other tasks or datasets.Comment: Workshop on Deep Vision, CVPR 202
Denoising Adversarial Autoencoders: Classifying Skin Lesions Using Limited Labelled Training Data
We propose a novel deep learning model for classifying medical images in the
setting where there is a large amount of unlabelled medical data available, but
labelled data is in limited supply. We consider the specific case of
classifying skin lesions as either malignant or benign. In this setting, the
proposed approach -- the semi-supervised, denoising adversarial autoencoder --
is able to utilise vast amounts of unlabelled data to learn a representation
for skin lesions, and small amounts of labelled data to assign class labels
based on the learned representation. We analyse the contributions of both the
adversarial and denoising components of the model and find that the combination
yields superior classification performance in the setting of limited labelled
training data.Comment: Under consideration for the IET Computer Vision Journal special issue
on "Computer Vision in Cancer Data Analysis
Graph-based classification of multiple observation sets
We consider the problem of classification of an object given multiple
observations that possibly include different transformations. The possible
transformations of the object generally span a low-dimensional manifold in the
original signal space. We propose to take advantage of this manifold structure
for the effective classification of the object represented by the observation
set. In particular, we design a low complexity solution that is able to exploit
the properties of the data manifolds with a graph-based algorithm. Hence, we
formulate the computation of the unknown label matrix as a smoothing process on
the manifold under the constraint that all observations represent an object of
one single class. It results into a discrete optimization problem, which can be
solved by an efficient and low complexity algorithm. We demonstrate the
performance of the proposed graph-based algorithm in the classification of sets
of multiple images. Moreover, we show its high potential in video-based face
recognition, where it outperforms state-of-the-art solutions that fall short of
exploiting the manifold structure of the face image data sets.Comment: New content adde
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