  We present MosaicFusion, a simple yet effective diffusion-based data
augmentation approach for large vocabulary instance segmentation. Our method is
training-free and does not rely on any label supervision. Two key designs
enable us to employ an off-the-shelf text-to-image diffusion model as a useful
dataset generator for object instances and mask annotations. First, we divide
an image canvas into several regions and perform a single round of diffusion
process to generate multiple instances simultaneously, conditioning on
different text prompts. Second, we obtain corresponding instance masks by
aggregating cross-attention maps associated with object prompts across layers
and diffusion time steps, followed by simple thresholding and edge-aware
refinement processing. Without bells and whistles, our MosaicFusion can produce
a significant amount of synthetic labeled data for both rare and novel
categories. Experimental results on the challenging LVIS long-tailed and
open-vocabulary benchmarks demonstrate that MosaicFusion can significantly
improve the performance of existing instance segmentation models, especially
for rare and novel categories. Code will be released at
https://github.com/Jiahao000/MosaicFusion.
