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Digitizing a graph/plot

  • To: mathgroup at
  • Subject: [mg8628] Digitizing a graph/plot
  • From: SESSELMANN ROLAND <sesselma at engine.Colorado.EDU>
  • Date: Fri, 12 Sep 1997 04:10:42 -0400
  • Sender: owner-wri-mathgroup at

I have a graph stored as a graphics file (i.e. JPG) and would like to
digitize it.

In Mama one can click on the graph, hold down the ALT key, and move the
mouse cursor around to see the coordinates. This works fine.

Is there a way to directly copy specific coordinates i.e. into the next
input line rather than only seeing these coordinate (lower left corner
of the notebook) and have to type them in by hand for further use?

Here is the "big picture" of what I want to do:

I found a figure in a paper which contains a plot of a function.
Unfortunately the functional form is not given so I have to pick a few
points of the function and do a curve fit to get a functional form. There
are many possibilities to do this, i.e. using a pencil and a ruler or
writing a sophisticated image processing program. For my purposes I need
something in between. What I did is I scanned in the figure i.e. as a JPG
file, open it with Mama, found the coordinates of points along the
function, typed in the coordinates by hand again and did a curve fit 
(using appropriate scale factors to match the coordinate systems).

Does someone have an idea of how to simplify this process preferably with
Mama but also other programs? (I do not like the "typing in by hand"   
part ...) I am using Mama 3.0 and 2.2 on all platforms (Unix, Linux, W95,

Thank you!

Roland Sesselmann
sesselma at

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