  This paper studies few-shot segmentation, which is a task of predicting
foreground mask of unseen classes by a few of annotations only, aided by a set
of rich annotations already existed. The existing methods mainly focus the task
on "\textit{how to transfer segmentation cues from support images (labeled
images) to query images (unlabeled images)}", and try to learn efficient and
general transfer module that can be easily extended to unseen classes. However,
it is proved to be a challenging task to learn the transfer module that is
general to various classes. This paper solves few-shot segmentation in a new
perspective of "\textit{how to represent unseen classes by existing classes}",
and formulates few-shot segmentation as the representation process that
represents unseen classes (in terms of forming the foreground prior) by
existing classes precisely. Based on such idea, we propose a new class
representation based few-shot segmentation framework, which firstly generates
class activation map of unseen class based on the knowledge of existing
classes, and then uses the map as foreground probability map to extract the
foregrounds from query image. A new two-branch based few-shot segmentation
network is proposed. Moreover, a new CAM generation module that extracts the
CAM of unseen classes rather than the classical training classes is raised. We
validate the effectiveness of our method on Pascal VOC 2012 dataset, the value
FB-IoU of one-shot and five-shot arrives at 69.2\% and 70.1\% respectively,
which outperforms the state-of-the-art method.
