压缩越狠生成越好,新方法让模型用更少参数实现更高效率。
When Worse is Better: Navigating the compression-generation tradeoff in visual tokenization
- 用生成模型能力反推压缩策略,优化潜空间表示
- 新方法在保持压缩率前提下提升生成质量,效率提升2-3倍
- 仅用一半令牌和四分之一参数达到同类模型性能
当前图像生成多采用两阶段训练:第一阶段用自编码器将图像压缩至潜空间,第二阶段训练生成模型学习该潜空间分布。本文研究这一过程中的压缩-生成权衡问题。基于缩放定律分析发现,对小型生成模型而言,更激进的压缩即使降低重建质量,反而有助于提升生成效果。进一步探究计算量与压缩率-失真权衡的关系后,提出因果正则化分词(CRT)方法,利用生成建模过程的知识,在潜空间嵌入有益归纳偏置。该方法在不改变压缩率、仅轻微影响失真情况下,显著提升生成性能,实现2-3倍的计算效率提升。结合进一步优化,所提方案仅需256个令牌(原为576),775M参数(原为3.1B),即达成与LlamaGen-3B相当的生成效果(FID=2.18),且使用相同架构与推理流程。
原文摘要 · Abstract (English)
Current image generation methods are based on a two-stage training approach. In stage 1, an auto-encoder is trained to compress an image into a latent space; in stage 2, a generative model is trained to learn a distribution over that latent space. This reveals a fundamental trade-off, do we compress more aggressively to make the latent distribution easier for the stage 2 model to learn even if it makes reconstruction worse? We study this problem in the context of discrete, auto-regressive image generation. Through the lens of scaling laws, we show that smaller stage 2 models can benefit from more compressed stage 1 latents even if reconstruction performance worsens, demonstrating that generation modeling capacity plays a role in this trade-off. Diving deeper, we rigorously study the connection between compute scaling and the stage 1 rate-distortion trade-off. Next, we introduce Causally Regularized Tokenization (CRT), which uses knowledge of the stage 2 generation modeling procedure to embed useful inductive biases in stage 1 latents. This regularization improves stage 2 generation performance better by making the tokens easier to model without affecting the stage 1 compression rate and marginally affecting distortion: we are able to improve compute efficiency 2-3$\times$ over baseline. Finally, we use CRT with further optimizations to the visual tokenizer setup to result in a generative pipeline that matches LlamaGen-3B generation performance (2.18 FID) with half the tokens per image (256 vs. 576) and a fourth the total model parameters (775M vs. 3.1B) while using the same architecture and inference procedure.
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