A WebPlotDigitizer alternative that does the clicking for you
WebPlotDigitizer is free and open source. It works from an image of the chart: you calibrate the axes by clicking four known points, then pick out the data. Chart to Data reads the axes and the points for you, takes a whole paper at once, and reads charts inside PDFs exactly.
What Chart to Data does for you
- No axis calibration. The axis numbers are read from the chart, including log axes, date axes and a second y axis.
- A whole paper at once. Upload the PDF and every chart on every page comes back, each on its own sheet.
- Exact values from PDFs. When a PDF holds the chart as a drawing (most figures in papers do), the values are read from the drawing itself. Nothing is estimated from pixels, so a point is as precise as the file is.
- Every value shown on the chart, so checking takes a look, not a recount.
- An Excel file with an audit sheet: the source page and the method for every chart, and every value changed by hand.
- Free for charts in PDFs, without limit and without an account.
Which tool for which figure
Chart to Data reads the figures most papers are made of: bar charts, line charts, scatter plots, pie charts and survival curves, with error bars, log axes, date axes and two y axes. For those there is nothing to set up: a chart in a PDF comes back in a couple of seconds, exact.
WebPlotDigitizer also lists polar diagrams, ternary diagrams and maps among its chart types. Chart to Data does not read those, so keep it for them.
And when a reading here misses something, you are not sent back to the start. Click the missing point in, or click two places on an axis and type their values, as you would by hand. You begin from the automatic reading and only click what it missed.
Small, crowded figures are the hard case for pictures: when a plot is only a couple of hundred pixels high, a pixel is already a visible error. Use the PDF when you have it, or a larger screenshot.
How to try it
- Drop a graph image or a PDF on the page.
- Look at the rings drawn on the chart: each is one value.
- Correct anything that is off in the table, then download Excel or CSV.
Questions
Is it free?
Charts drawn inside PDFs are read free, without limit. One picture a day is free too. More pictures are sold in packs, paid once.
Do I need an account?
No. Drop the file and the data comes back. Files are read and then discarded.
What if it misses a point or a whole series?
Add it by clicking, as you would in WebPlotDigitizer: choose the series, or name a missing one, and click each point on the chart. Each click is read from the axes at that place. If an axis itself was read wrongly, click two places on it and type their values, and every value on that axis is read again. The Excel file marks everything added or changed by hand.