Graph Data Extractor
Turn a chart image back into numbers: set the axes, click the points, export the data
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Calibrates the axes of a chart image and turns the points you click into X and Y numbers. Use it when a paper or report shows a graph but not the data behind it.
How to use
- Drop the chart image on the page, or click to choose it.
- Under "Axis calibration", click two points on the X axis (X1, X2) and two on the Y axis (Y1, Y2), then enter their real values. Tick "X axis is logarithmic" or "Y axis is logarithmic" if needed.
- With "Add data points", click each point; its values appear under "Extracted data". Use "Add series" for several lines.
- For a long curve, use "Pick curve colour" and "Extract into the selected series", then check the points against the image.
- Take the data with "Copy (tab-separated)" or "Save as CSV".
How it works
- The four axis points define an affine transform from pixels to values, so slightly rotated scans are read correctly. Log axes are interpolated in log values.
- In "Bar chart" mode you calibrate two points on the value axis and click the top of each bar. Enter a date axis as numbers, such as years.
- Automatic extraction looks only at colour and can be wrong. Work on each image is saved in this browser, so reopening the image continues it.
Questions and answers
- How do I extract data from a graph image?
- Calibrate the axes with four ticks whose values you know, then click the data points. Each point's X and Y values are listed in the table at once.
- How accurate are the extracted values?
- It depends on the image resolution and where you click. Put the axis points on ticks far apart, zoom in and use the "Magnifier".
- Does it work with logarithmic axes?
- Yes. Tick the log option for that axis. Values on a log axis must be greater than 0.
- Is my image uploaded to a server?
- No. The image is processed inside your browser and is not sent anywhere.