在机器学习中,生成模型可以用来直接对数据建模(例如根据某个变量的概率密度函数进行数据采样),也可以用来建立变量间的条件概率分布。条件概率分布可以由生成模型根据贝叶斯定理形成。

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面对人工标注大量样本费时费力,一些稀有类别样本难于获取等问题,零样本图像分类成为计算机视觉领域的一个研究热点。首先,对零样本学习,包括直推式零样本学习和归纳式零样本学习进行了简单介绍;其次,重点介绍了基于空间嵌入零样本图像分类方法和基于生成模型零样本图像分类方法以及它们的子类方法,并对这些方法的机制、优缺点和适用场景等进行了分析和总结;然后,简单介绍了零样本图像分类常用数据集和评估方法,并对典型零样本图像分类方法进行了性能比较;接着,指出了现有零样本图像分类中存在的领域漂移、枢纽点和语义鸿沟等问题及相应的解决思路;最后,对零样本图像分类未来发展趋势和研究热点,如判别性区域的准确定位、生成高质量不可见类视觉特征、广义零样本图像分类等进行了探讨。

http://fcst.ceaj.org/CN/abstract/abstract2683.shtml

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Discrete-time diffusion-based generative models and score matching methods have shown promising results in modeling high-dimensional image data. Recently, Song et al. (2021) show that diffusion processes that transform data into noise can be reversed via learning the score function, i.e. the gradient of the log-density of the perturbed data. They propose to plug the learned score function into an inverse formula to define a generative diffusion process. Despite the empirical success, a theoretical underpinning of this procedure is still lacking. In this work, we approach the (continuous-time) generative diffusion directly and derive a variational framework for likelihood estimation, which includes continuous-time normalizing flows as a special case, and can be seen as an infinitely deep variational autoencoder. Under this framework, we show that minimizing the score-matching loss is equivalent to maximizing a lower bound of the likelihood of the plug-in reverse SDE proposed by Song et al. (2021), bridging the theoretical gap.

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Discrete-time diffusion-based generative models and score matching methods have shown promising results in modeling high-dimensional image data. Recently, Song et al. (2021) show that diffusion processes that transform data into noise can be reversed via learning the score function, i.e. the gradient of the log-density of the perturbed data. They propose to plug the learned score function into an inverse formula to define a generative diffusion process. Despite the empirical success, a theoretical underpinning of this procedure is still lacking. In this work, we approach the (continuous-time) generative diffusion directly and derive a variational framework for likelihood estimation, which includes continuous-time normalizing flows as a special case, and can be seen as an infinitely deep variational autoencoder. Under this framework, we show that minimizing the score-matching loss is equivalent to maximizing a lower bound of the likelihood of the plug-in reverse SDE proposed by Song et al. (2021), bridging the theoretical gap.

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