Plot Digitizer

Plot Digitizer is a Java‑based utility that converts scanned images of X‑Y plots into numeric data. Users load GIF, JPEG, or PNG files of line or scatter plots, then click on individual points to record their coordinates, which can be exported to a text file for further analysis. The tool supports both linear and logarithmic axes and includes functions for inserting, deleting, or moving points, as well as calculating curve lengths and polygon areas.

The application offers zooming, unlimited undo/redo, and the ability to save calibration settings for reuse on the same image. Users can recalibrate the Y axis independently of the X axis, which is useful when multiple data sets share a common horizontal scale. A semi‑automatic digitizing mode is available that relies on the external open‑source autotrace program to trace lines when a brush‑styled selection is made, though this feature works best with high‑resolution black‑and‑white images and is not supported on Windows.

Plot Digitizer is targeted at researchers, engineers, or anyone who needs to extract numerical values from printed or scanned graphs, technical drawings, and orthographic photographs. It runs on macOS, is classified as stable, and is distributed through SourceForge.