Reproduce “ALTo: Adaptive-Length Tokenizer for Autoregressive Mask Generation” on OpenResearch

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About this paper

Lingfeng Wang, Hualing Lin, Senda Chen, Tao Wang, Changxu Cheng, Yangyang Zhong, Dong Zheng, Wuyue Zhao

ALTo learns to stop mask-token generation according to the complexity of a segmentation mask, allowing an MLLM to produce shorter outputs for simpler shapes and longer ones when needed. On referring-expression segmentation benchmarks, it generally maintains or improves mask quality while reducing generated mask sequences from 32 tokens to roughly 16–19 tokens and lowering measured generation time.

Key insights

  • Mask sequence length can be learned from reconstruction quality: an added token is encouraged only when its expected benefit justifies the length penalty.
  • High-resolution pixel features and training on complex multi-target masks contribute to mask quality; removing the pixel encoder lowers reconstruction gIoU from 94.4 to 91.9.
  • GRPO primarily adjusts efficiency rather than accuracy: on gRefCOCO validation, it reduces average length from 17.5 to 15.7 tokens with only a small change in cIoU/gIoU.

Summary by alphaXiv.

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