Automated data extraction of bar chart raster images

TL;DR

This paper presents an automated method using OCR to extract data from bar chart images, aiming to facilitate meta-analyses by reducing manual effort and improving accuracy.

Contribution

The authors developed a multistep OCR-based software for automatic data extraction from bar charts, with validation against manual methods showing high agreement.

Findings

91.8% of data points within limits of agreement

Automated extraction accuracy: X-axis labels 79.5%, Y-tick 88.6%, bar values <5% error 88.0%

Potential improvements include neural network-based redundancy checks

Abstract

Objective: To develop software utilizing optical character recognition toward the automatic extraction of data from bar charts for meta-analysis. Methods: We utilized a multistep data extraction approach that included figure extraction, text detection, and image disassembly. PubMed Central papers that were processed in this manner included clinical trials regarding macular degeneration, a disease causing blindness with a heavy disease burden and many clinical trials. Bar chart characteristics were extracted in both an automated and manual fashion. These two approaches were then compared for accuracy. These characteristics were then compared using a Bland-Altman analysis. Results: Based on Bland-Altman analysis, 91.8% of data points were within the limits of agreement. By comparing our automated data extraction with manual data extraction, automated data extraction yielded the following accuracies: X-axis labels 79.5%, Y-tick values 88.6%, Y-axis label 88.6%, Bar value <5% error 88.0%. Discussion: Based on our analysis, we achieved an agreement between automated data extraction and manual data extraction. A major source of error was the incorrect delineation of 7s as 2s by optical character recognition library. We also would benefit from adding redundancy checks in the form of a deep neural network to boost our bar detection accuracy. Further refinements to this method are justified to extract tabulated and line graph data to facilitate automated data gathering for meta-analysis.