Graph Digitization

Graph digitization is the process of obtaining original data from a plot when the data values are not available.  What does that mean?  Often scientific plots are found in journal papers or textbooks.  These plots are either in an electronic format (TIFF, PNG, etc) or are a paper copy which can be scanned and saved in an electronic format.  It is often necessary to recreate the plot or get parameter values to a higher precision than can be obtained with the naked eye.  This is when you would use graph digitization software.

Although many software packages exist to digitize plots, only one will be introduced here.  The GetData Graph Digitizer is adequate for most applications and has a free trial download.

GetData Graph Digitizer

The GetData graph digitizer can downloaded from www.getdata-graph-digitizer.com.  The download is for a trial version which has a limited duration.  If you find you need to software often a personal license can be purchased online for $30.00 which also opens additional features.

GetData allows for the digitization of TIFF, JPEC, BMP, and PCX formats.  The plot data can be digitized automatically or manually.

General Tips on using GetData: 

·         The automatic plot digitization option should be used when you only have one series of data contained in the figure.

·         The manual digitization is helpful if your plot is of poor quality, has gridlines, or has multiple series of data plotted within the same figure.

·         The output data points can easily be copied and pasted into plotting packages such as Excel, Matlab, KaleidaGraph, etc. 

How accurate is the Graph Digitization?

Let’s find out.  Here is a Matlab script that you can use to generate a plot if the sinc function.  Paste this into a new m file within Matlab and run it.

            %Define the x-axis

x = -10:0.2:10;

%Define the function

y = sinc(x);

%Plot the output

plot(x,y,'k.')

xlabel('x')

ylabel('f(x)')

ylim([-0.5,1.2])

xlim([-10,10])

 

Now save the plot as a “.bmp”.
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