Understanding charts requires models to jointly reason over geometric visual patterns, structured numerical data, and natural language -- a capability where current vision-language models (VLMs) remain limited. We introduce ChartNet, a high-quality, million-scale multimodal dataset designed to advance chart interpretation and reasoning. ChartNet leverages a novel code-guided synthesis pipeline to generate 1.5 million diverse chart samples spanning 24 chart types and 6 plotting libraries. Each sample consists of five aligned components: plotting code, rendered chart image, data table, natural language summary, and question-answering with reasoning, providing fine-grained cross-modal alignment. To capture the full spectrum of chart comprehension, ChartNet additionally includes specialized subsets encompassing human annotated data, real-world data, safety, and grounding. Moreover, a rigorous quality-filtering pipeline ensures visual fidelity, semantic accuracy, and diversity across chart representations. Fine-tuning on ChartNet consistently improves results across benchmarks, demonstrating its utility as large-scale supervision for multimodal models. As the largest open-source dataset of its kind, ChartNet aims to support the development of foundation models with robust and generalizable capabilities for data visualization understanding. The dataset is publicly available at https://huggingface.co/datasets/ibm-granite/ChartNet
@article{arxiv.2603.27064,
title = {ChartNet: A Million-Scale, High-Quality Multimodal Dataset for Robust Chart Understanding},
author = {Jovana Kondic and Pengyuan Li and Dhiraj Joshi and Isaac Sanchez and Ben Wiesel and Shafiq Abedin and Amit Alfassy and Eli Schwartz and Daniel Caraballo and Yagmur Gizem Cinar and Florian Scheidegger and Steven I. Ross and Daniel Karl I. Weidele and Hang Hua and Ekaterina Arutyunova and Roei Herzig and Zexue He and Zihan Wang and Xinyue Yu and Yunfei Zhao and Sicong Jiang and Minghao Liu and Qunshu Lin and Peter Staar and Luis Lastras and Aude Oliva and Rogerio Feris},
journal= {arXiv preprint arXiv:2603.27064},
year = {2026}
}