Table Detection for Visually Rich Document Images

Table Detection (TD) is a fundamental task towards visually rich document understanding. Current studies usually formulate the TD problem as an object detection problem, then leverage Intersection over Union (IoU) based metrics to evaluate the model performance and IoU-based loss functions to optimize the model. TD applications usually require the prediction results to cover all the table contents and avoid information loss. However, IoU and IoU-based loss functions cannot directly reflect the degree of information loss for the prediction results. Therefore, we propose to decouple IoU into a ground truth coverage term and a prediction coverage term, in which the former can be used to measure the information loss of the prediction results. Besides, tables in the documents are usually large, sparsely distributed, and have no overlaps because they are designed to summarize essential information to make it easy to read and interpret for human readers. Therefore, in this study, we use SparseR-CNN as the base model, and further improve the model by using Gaussian Noise Augmented Image Size region proposals and many-to-one label assignments. To demonstrate the effectiveness of proposed method and compare with state-of-the-art methods fairly, we conduct experiments and use IoU-based evaluation metrics to evaluate the model performance. The experimental results show that the proposed method can consistently outperform state-of-the-art methods under different IoU-based metric on a variety of datasets. We conduct further experiments to show the superiority of the proposed decoupled IoU for the TD applications by replacing the IoU-based loss functions and evaluation metrics with proposed decoupled IoU counterparts. The experimental results show that our proposed decoupled IoU loss can encourage the model to alleviate information loss.