How to turn a plot image into pgfplots with the real data

#tutorial #productivity #writing

You want to reproduce a plot from another paper in your own document, in your own style, or compare your results against it. Pasting the image looks out of place and cannot be edited. Here is how to get a pgfplots figure with the measured data points instead.

The quick way

Snip the plot in CatchTeX's PDF viewer (Ctrl+O) or from the screen (Ctrl+Alt+T). Include
the axes, tick labels and legend.
Auto mode recognises a plot; you can also pick the Plot chip.
Compare the compiled pgfplots preview with the original snip.
Copy LaTeX (Ctrl+Shift+C): you get a pgfplots axis with one
\addplot per series, ready for Overleaf, together with the packages it needs.

\begin{tikzpicture}
\begin{axis}[xlabel={Epoch}, ylabel={Accuracy},
xmin=0, xmax=50, ymin=0, ymax=1, legend pos=south east]
\addplot coordinates {(0,0.08) (5,0.41) (10,0.66) (20,0.83) (50,0.91)};
\addlegendentry{Ours}
\addplot coordinates {(0,0.07) (5,0.29) (10,0.48) (20,0.66) (50,0.78)};
\addlegendentry{Baseline}
\end{axis}
\end{tikzpicture}

How it measures the data

CatchTeX reads the axis tick labels, maps pixel positions to data values, separates the series
and samples each curve. It is deterministic image analysis, not a guess by an
AI model, so the same snip always gives the same numbers. On our test set it finds 37 of 38 series,
with a mean error of 0.45 % of the axis range, and reads all 40 axis labels.

The data are as precise as the picture: a small, low-resolution plot gives coarser values. Zoom
in before you snip, and check the preview against the original.

Other ways, compared

Method	Data you can edit	LaTeX output	Effort
Include the image (\includegraphics)	No	Picture only, other fonts	None
WebPlotDigitizer / Engauge Digitizer	Yes (CSV)	No: write the pgfplots code yourself	Calibrate axes, click or trace each series
Ask the authors for the data	Yes	No	Days, if they answer
CatchTeX	Yes, in the code	Complete pgfplots figure, compiled	One snip

Tips

Restyle freely: change colours, line styles and fonts in the axis options so the
figure matches the rest of your document.
Cite the source of the data in the caption, as you would for a reproduced figure.
Need the numbers in a table instead? Copy the coordinates from the code into a
pgfplotstable or a spreadsheet.

Try it on your own paper

CatchTeX is free for Windows, Mac and Linux: every mode, works offline, nothing to set up.

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Originally published at catchtex.com/guides/plot-image-to-pgfplots.

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