Oliver Tueselmann and Gernot A. Fink
Int. Journal on Document Analysis and Recognition, 2024.
Semantic analysis of handwritten document images offers a wide range of practical application scenarios. A sequential combination of handwritten text recognition (HTR) and a task-specific natural language processing system offers an intuitive solution in this domain. However, this HTR-based approach suffers from the problem of error propagation. An HTR-free model, which avoids explicit text recognition and solves the task end-to-end, tackles this problem, but often produces poor results. A possible reason for this is that it does not incorporate largely pre-trained semantic word embeddings, which turn out to be one of the most powerful advantages in the textual domain. In this work, we propose an HTR-based and an HTR-free model and compare them on a variety of segmentation-based handwritten document image benchmarks including semantic word spotting, named entity recognition, and question answering. Furthermore, we propose a cross-modal knowledge distillation approach to integrate semantic knowledge from textually pre-trained word embeddings into HTR-free models. In a series of experiments, we investigate optimization strategies for robust semantic word image representation. We show that the incorporation of semantic knowledge is beneficial for HTR-free approaches in achieving state-of-the-art results on a variety of benchmarks.