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Convert images to data with Plot Digitizer

You’re scouring the internet for data to prove your point…
After hours of searching, you finally found it!
One problem – it’s a chart in a pdf…

Charts are better than nothing, but you really want to have the numbers in Excel or Matlab so you can do analysis and get big insights (or at least make a nicer-looking chart).

The answer is Plot Digitizer

Below is a short tutorial on using this tool to go from chart to data faster and more accurately than simply “eye-balling” it.

Using Plot Digitizer

Step 1. Download Plot Digitizer. Then unzip the files to someplace safe (e.g., Program Files, Applications, etc.).

Step 2. Get the chart. Save a .png file of the graph you’d like to digitize (.png files work best because they use loss-less compression and Plot Digitizer can read them). A screenshot is usually the easiest way to grab the chart. (simple tutorial on screenshots). Also, remember to zoom in before taking the screenshot so it’s nice and big.

Step 3. Start up. Run PlotDigitzer (just double-click the .exe) and open the .png image.

Step 4. Calibrate the axes. You’ll jump right into calibration when you open the image. The cursor becomes a cross-hairs, and instructions appear at the bottom of the screen. Start by clicking the far left side of the x axis, and entering the value when prompted. Remember to click where the data is defined (e.g., click in the center of first bar in the example below).

Continue calibrating by clicking the far-right end of the x axis, both extremes of the y axis, and labeling both axes.

Step 5. Digitize. Click on each datapoint in the chart that you’d like to capture. You can do this multiple times if the chart has multiple data series (e.g., in a multi-line line chart or a bar chart with split bars). Try to click as close as possible to the true spot on the chart. If you miss a point you can always undo clicks with the button at the top.

When you finish, click “Done” at the far right of the second toolbar.

Step 6. Export the data. Either select the cells in the output windows and paste the data into Excel, or go to “File->Save As” to save a .csv file.

Use that data

And there you have it! You now have (almost) the exact data used to generate the chart. If you’ve got any other tricks to extract data from onerous sources, let us know in the comments!

  1. zaidi
    January 1st, 2013 at 01:43 | #1

    thnks for a very usefull information

  2. April 6th, 2015 at 02:43 | #2

    You can also use im2graph, see http://www.im2graph.co.il
    im2graph is free and available on Linux and Windows.

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