Edge Guided GANs with Multi-Scale Contrastive Learning for Semantic
  Image Synthesis
Hao Tang Guolei Sun Nicu Sebe Luc Van Gool
We propose a novel ECGAN for the challenging semantic image synthesis task.
Although considerable improvements have been achieved by the community in the
recent period, the quality of synthesized images is far from satisfactory due
to three largely unresolved challenges. 1) The semantic labels do not provide
detailed structural information, making it challenging to synthesize local
details and structures; 2) The widely adopted CNN operations such as
convolution, down-sampling, and normalization usually cause spatial resolution
loss and thus cannot fully preserve the original semantic information, leading
to semantically inconsistent results (e.g., missing small objects); 3) Existing
semantic image synthesis methods focus on modeling 'local' semantic information
from a single input semantic layout. However, they ignore 'global' semantic
information of multiple input semantic layouts, i.e., semantic cross-relations
between pixels across different input layouts. To tackle 1), we propose to use
the edge as an intermediate representation which is further adopted to guide
image generation via a proposed attention guided edge transfer module. To
tackle 2), we design an effective module to selectively highlight
class-dependent feature maps according to the original semantic layout to
preserve the semantic information. To tackle 3), inspired by current methods in
contrastive learning, we propose a novel contrastive learning method, which
aims to enforce pixel embeddings belonging to the same semantic class to
generate more similar image content than those from different classes. We
further propose a novel multi-scale contrastive learning method that aims to
push same-class features from different scales closer together being able to
capture more semantic relations by explicitly exploring the structures of
labeled pixels from multiple input semantic layouts from different scales.