  In this work, we focus on open vocabulary instance segmentation to expand a
segmentation model to classify and segment instance-level novel categories.
Previous approaches have relied on massive caption datasets and complex
pipelines to establish one-to-one mappings between image regions and words in
captions. However, such methods build noisy supervision by matching non-visible
words to image regions, such as adjectives and verbs. Meanwhile, context words
are also important for inferring the existence of novel objects as they show
high inter-correlations with novel categories. To overcome these limitations,
we devise a joint \textbf{Caption Grounding and Generation (CGG)} framework,
which incorporates a novel grounding loss that only focuses on matching object
nouns to improve learning efficiency. We also introduce a caption generation
head that enables additional supervision and contextual modeling as a
complementation to the grounding loss. Our analysis and results demonstrate
that grounding and generation components complement each other, significantly
enhancing the segmentation performance for novel classes. Experiments on the
COCO dataset with two settings: Open Vocabulary Instance Segmentation (OVIS)
and Open Set Panoptic Segmentation (OSPS) demonstrate the superiority of the
CGG. Specifically, CGG achieves a substantial improvement of 6.8% mAP for novel
classes without extra data on the OVIS task and 15% PQ improvements for novel
classes on the OSPS benchmark.
