Language models are defined over a finite set of inputs, which creates a
vocabulary bottleneck when we attempt to scale the number of supported
languages. Tackling this bottleneck results in a trade-off between what can be
represented in the embedding matrix and computational issues in the output
layer. This paper introduces PIXEL, the Pixel-based Encoder of Language, which
suffers from neither of these issues. PIXEL is a pretrained language model that
renders text as images, making it possible to transfer representations across
languages based on orthographic similarity or the co-activation of pixels.
PIXEL is trained to reconstruct the pixels of masked patches, instead of
predicting a distribution over tokens. We pretrain the 86M parameter PIXEL
model on the same English data as BERT and evaluate on syntactic and semantic
tasks in typologically diverse languages, including various non-Latin scripts.
We find that PIXEL substantially outperforms BERT on syntactic and semantic
processing tasks on scripts that are not found in the pretraining data, but
PIXEL is slightly weaker than BERT when working with Latin scripts.
Furthermore, we find that PIXEL is more robust to noisy text inputs than BERT,
further confirming the benefits of modelling language with pixels.

该文章介绍了 PIXEL，一种基于像素的预训练语言模型，通过将文本渲染为图像，PIXEL 可以处理不同语言，特别是非拉丁文字。实验发现 PIXEL 在语法和语义处理方面表现优异，且对于噪声文本的输入更为稳健。