[Image-SIG] experimental data diagram digitalization

[tomislav_maric@gmx.com]

@Edward Cannon

Hi Edward, 

Thanks for the advice. Well, I am not getting any of the experimental data, any time soon. Since I am dealing with the sonic pressure values up to 600 kPa, I basically have one peak, and the rest is low amplitude noise about 0 kPa... [0,600] leaves me a lot of tolerance to work with. This is just for the specific cases I am dealing with now. Besides, I'm using this to evaluate the numerical studies vs the experimental data, so I am very happy with a coarse estimate, for now. Anyway, thanks a lot for the advice. 

Best regards, 
Tomislav

> ----- Original Message -----
> From: Edward Cannon
> Sent: 11/26/10 08:10 PM
> To: tomislav_maric at gmx.com
> Subject: Re: [Image-SIG] experimental data diagram digitalization
> 
> Your approach sounds pretty good, It will probably work. I might offer
> this piece of advice: don't do it. Data looses precision as it is
> graphed, and especially in the low resolutions used in many pdf
> versions of articles. The descriptive statistics you compute are
> likely to be incorrect. If you need the original data get it from a
> publication or the paper author. If you intend to publish any results,
> no journal will accept your recreated data.
> Edward Cannon
> Unicorn School
> 
> On Fri, Nov 26, 2010 at 2:45 AM, tomislav_maric at gmx.com
> <tomislav.maric at gmx.com> wrote:
> > Hi everyone,
> >
> > I need to digitalize a diagram of experimental data. I have been reading the documentation of the Python Imaging Library, and I'm thinking that I can approach my problem in the following way:
> >
> > 1) Create a .png of the diagram I find in the literature (.pdf articles, or theses).
> > 2) Clean up the diagram (remove the axes, the text and leave only the data that I am interested in).
> > 3) Read the image.
> > 4) Apply a filter that will result in only those pixels that are non-white (pick up the experimental data).
> > 5) Scale the result data of the filter (in pixels) to the actual coordinates in the image in milimeters.
> > 6) Scale the milimeter coordinates to the actual scale of the diagram (read from the original .pdf), to get the
> >    true coordinates (in my case, I have time in seconds and pressure in kPa).
> >
> > Can this be done with the Python Imaging Library + some additional python coding?
> >
> > The other option would be to use inkscape to export the path into .svg and manipulate (scale) it with some python-XML library.
> >
> > Can anyone give me some advice on this issue?
> >
> > Thanks in advance,
> > Tomislav
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