In Defense of Scene Graphs for Image Captioning

TL;DR

This paper introduces SG2Caps, a scene graph-based image captioning framework that relies solely on scene graph labels, achieving competitive performance while reducing computational complexity.

Contribution

SG2Caps demonstrates that scene graph labels alone can be effectively used for image captioning, eliminating the need for CNN features and reducing model complexity.

Findings

Outperforms existing scene graph-only captioning models significantly.

Achieves 49% fewer trainable parameters compared to traditional methods.

Leverages spatial and HOI labels to bridge semantic gaps in scene graphs.

Abstract

The mainstream image captioning models rely on Convolutional Neural Network (CNN) image features to generate captions via recurrent models. Recently, image scene graphs have been used to augment captioning models so as to leverage their structural semantics, such as object entities, relationships and attributes. Several studies have noted that the naive use of scene graphs from a black-box scene graph generator harms image captioning performance and that scene graph-based captioning models have to incur the overhead of explicit use of image features to generate decent captions. Addressing these challenges, we propose \textbf{SG2Caps}, a framework that utilizes only the scene graph labels for competitive image captioning performance. The basic idea is to close the semantic gap between the two scene graphs - one derived from the input image and the other from its caption. In order to achieve this, we leverage the spatial location of objects and the Human-Object-Interaction (HOI) labels as an additional HOI graph. SG2Caps outperforms existing scene graph-only captioning models by a large margin, indicating scene graphs as a promising representation for image captioning. Direct utilization of scene graph labels avoids expensive graph convolutions over high-dimensional CNN features resulting in 49% fewer trainable parameters. Our code is available at: https://github.com/Kien085/SG2Caps