2,431 research outputs found
CoopHash: Cooperative Learning of Multipurpose Descriptor and Contrastive Pair Generator via Variational MCMC Teaching for Supervised Image Hashing
Leveraging supervised information can lead to superior retrieval performance
in the image hashing domain but the performance degrades significantly without
enough labeled data. One effective solution to boost the performance is to
employ generative models, such as Generative Adversarial Networks (GANs), to
generate synthetic data in an image hashing model. However, GAN-based methods
are difficult to train and suffer from mode collapse issue, which prevents the
hashing approaches from jointly training the generative models and the hash
functions. This limitation results in sub-optimal retrieval performance. To
overcome this limitation, we propose a novel framework, the generative
cooperative hashing network (CoopHash), which is based on the energy-based
cooperative learning. CoopHash jointly learns a powerful generative
representation of the data and a robust hash function. CoopHash has two
components: a top-down contrastive pair generator that synthesizes contrastive
images and a bottom-up multipurpose descriptor that simultaneously represents
the images from multiple perspectives, including probability density, hash
code, latent code, and category. The two components are jointly learned via a
novel likelihood-based cooperative learning scheme. We conduct experiments on
several real-world datasets and show that the proposed method outperforms the
competing hashing supervised methods, achieving up to 10% relative improvement
over the current state-of-the-art supervised hashing methods, and exhibits a
significantly better performance in out-of-distribution retrieval
On the Anatomy of MCMC-Based Maximum Likelihood Learning of Energy-Based Models
This study investigates the effects of Markov chain Monte Carlo (MCMC)
sampling in unsupervised Maximum Likelihood (ML) learning. Our attention is
restricted to the family of unnormalized probability densities for which the
negative log density (or energy function) is a ConvNet. We find that many of
the techniques used to stabilize training in previous studies are not
necessary. ML learning with a ConvNet potential requires only a few
hyper-parameters and no regularization. Using this minimal framework, we
identify a variety of ML learning outcomes that depend solely on the
implementation of MCMC sampling.
On one hand, we show that it is easy to train an energy-based model which can
sample realistic images with short-run Langevin. ML can be effective and stable
even when MCMC samples have much higher energy than true steady-state samples
throughout training. Based on this insight, we introduce an ML method with
purely noise-initialized MCMC, high-quality short-run synthesis, and the same
budget as ML with informative MCMC initialization such as CD or PCD. Unlike
previous models, our energy model can obtain realistic high-diversity samples
from a noise signal after training.
On the other hand, ConvNet potentials learned with non-convergent MCMC do not
have a valid steady-state and cannot be considered approximate unnormalized
densities of the training data because long-run MCMC samples differ greatly
from observed images. We show that it is much harder to train a ConvNet
potential to learn a steady-state over realistic images. To our knowledge,
long-run MCMC samples of all previous models lose the realism of short-run
samples. With correct tuning of Langevin noise, we train the first ConvNet
potentials for which long-run and steady-state MCMC samples are realistic
images.Comment: Code available at: https://github.com/point0bar1/ebm-anatom
- …