DigitGraph Spreadsheet and WebPlot Digitiser

Posted on 03/03/2020 by dougaj4

I have posted here previously a spreadsheet that allows XY data to be extracted from images of graphs, maps or other images of objects in a single plane: How to digitise a scanned image.

I have updated the instructions for the procedure to cover Excel’s new dynamic array feature, which can return an array of data from a function entered in a single cell.  The new version can be downloaded from:

DigitGraph2.zip

I also recently discovered the Webplot Digitizer program, that can either be used on-line, or as a download.  The download is free (with no advertising), with a button for voluntary donations.  The screen-shot below shows the downloaded version.  The program is considerably more sophisticated than my spreadsheet, providing not only a magnified image of the graph at the cursor location, but also allowing the option of either manual selection of data points, or a fully automated process to detect the graph line(s) and generate the data points.

Output from the WebPlot program (both manual and automated) is shown below plotted together with output from my Digitgraph function, showing close agreement for all three lines.

This entry was posted in Charts, Charts, Computing - general, Curve fitting, Drawing, Excel, UDFs, VBA and tagged , , , , , . Bookmark the permalink.

6 Responses to DigitGraph Spreadsheet and WebPlot Digitiser

  1. Patricio Galvan's avatar Patricio Galvan says:
    03/03/2020 at 11:17 pm

    great contribution. Thanks

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  2. Paul Halsema's avatar Paul Halsema says:
    04/03/2020 at 12:07 am

    Another option is Enguage Digitizer, http://markummitchell.github.io/engauge-digitizer/. I’ve used it off and on for many years.

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  3. dbwriting's avatar dbwriting says:
    04/03/2020 at 1:49 pm

    Wow. I’m going to try and see if this works for the PCA slab-on-grade method charts. I wonder if it will handle multi-line graphs.

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    • dougaj4's avatar dougaj4 says:
      06/03/2020 at 8:28 am

      I haven’t tried multi-line graphs, but the auto line detection uses the line colour, so if all the lines are the same colour I imagine it might have problems.
      But the manual method would have no problem at all, other than being a bit tedious.

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  4. Enrique's avatar Enrique says:
    29/07/2026 at 7:48 pm

    Hi Doug… it’s time to disclose here that Excel+VBA alone (no human intervention aside pressing a button) can now get the data of the graph. Not even one color, I can get a full set of colours (for any given number of series). I can say that my procedure includes:

    • BMP reading and filtering by colour (if needed, WIA will come to the rescue to convert IMG format to BMP).
    • point aggregation procedure… a bit tricky, but it’s an small algorithm
    • Douglas-Peucker algorithm round to flatten the mess of short segments fromthe aggregation.
    • If needed, a difference pass can fine-tune the final data series (to deal with breaks,…)

    And I should say that a SOTA AI model will nail all these steps in just a bunch of prompts. In the end will be no more than 1-1.2k lines of code, with no external dependencies. I have not worked a lot on the axis issue (I mean to detect the axis and the numbers there…) but I will also say that is PERFECTLY attained with:

    • Internal windows OCR… amazing piece of hidden software, I revived with just 100 lines of powershell code, and one day fighting with AI to get the work done
    • more of the first steps mentioned.

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