Padding Tone: A Mechanistic Analysis of Padding Tokens in T2I Models
Authors: name: Michael Toker; name: Ido Galil; name: Hadas Orgad; name: Rinon Gal; name: Yoad Tewel; name: Gal Chechik; name: Yonatan Belinkov
Published: 2025-01-12 08:36:38

Abstract: Text-to-image (T2I) diffusion models rely on encoded prompts to guide the
image generation process. Typically, these prompts are extended to a fixed
length by adding padding tokens before text encoding. Despite being a default
practice, the influence of padding tokens on the image generation process has
not been investigated. In this work, we conduct the first in-depth analysis of
the role padding tokens play in T2I models. We develop two causal techniques to
analyze how information is encoded in the representation of tokens across
different components of the T2I pipeline. Using these techniques, we
investigate when and how padding tokens impact the image generation process.
Our findings reveal three distinct scenarios: padding tokens may affect the
model's output during text encoding, during the diffusion process, or be
effectively ignored. Moreover, we identify key relationships between these
scenarios and the model's architecture (cross or self-attention) and its
training process (frozen or trained text encoder). These insights contribute to
a deeper understanding of the mechanisms of padding tokens, potentially
informing future model design and training practices in T2I systems.