Improving Augmentation and Evaluation Schemes for Semantic Image Synthesis
This work improves the quality of generated images for semantic image synthesis models, which is relevant for researchers and practitioners working with GANs and image generation.
This paper introduces a novel augmentation scheme for GAN-based semantic image synthesis models, which randomly warps object shapes in semantic label maps. This method leads to an average improvement of ~3 mIoU and ~10 FID points across COCO-Stuff, ADE20K, and Cityscapes datasets compared to vanilla models. Additionally, the paper proposes an improved evaluation scheme that addresses bias in existing quantification metrics.
Despite data augmentation being a de facto technique for boosting the performance of deep neural networks, little attention has been paid to developing augmentation strategies for generative adversarial networks (GANs). To this end, we introduce a novel augmentation scheme designed specifically for GAN-based semantic image synthesis models. We propose to randomly warp object shapes in the semantic label maps used as an input to the generator. The local shape discrepancies between the warped and non-warped label maps and images enable the GAN to learn better the structural and geometric details of the scene and thus to improve the quality of generated images. While benchmarking the augmented GAN models against their vanilla counterparts, we discover that the quantification metrics reported in the previous semantic image synthesis studies are strongly biased towards specific semantic classes as they are derived via an external pre-trained segmentation network. We therefore propose to improve the established semantic image synthesis evaluation scheme by analyzing separately the performance of generated images on the biased and unbiased classes for the given segmentation network. Finally, we show strong quantitative and qualitative improvements obtained with our augmentation scheme, on both class splits, using state-of-the-art semantic image synthesis models across three different datasets. On average across COCO-Stuff, ADE20K and Cityscapes datasets, the augmented models outperform their vanilla counterparts by ~3 mIoU and ~10 FID points.