Find yourself a hand drawn figure from the olden time but need to use it anyway for some reason? Fret not, let’s make a digital copy of that using, you guessed it, EXCEL (or really any spreadsheet app)!

First, we’ll need:

  1. Legit copy of MS Office, or Libre Office, or arrr!
  2. Hand-drawn figure, DUH!
  3. MS Paint, GIMP, Paint.net, or for the classy ones out there, Adobe Photoshop (arrr!!!)

Now here’s what I did.

scanned copy of the desired figure First, I obtain a scanned copy of the drawn figure I want to recreate. Note that the one on the right is scanned with a 100 dpi settings.

But why the 100 DPI (dots per inch) settings? This is important to precisely estimate the pixel position  of the data points in the graph. Anything higher would cram more pixels in the curve to the point where picking a representative pixel will be kinda difficult and anything lower will make the image less resolved.

After obtaining a fairly readable scan with no unnecessary details, I proceeded with correctly rotating the image such that the y-axis of the graph is as much vertical as possible and the x-axis as much horizontal. Remember that images will always be in Cartesian coordinates so a titled image will be a pain to recreate precisely.

Now that’s out of the way, we begin with the fun part: Dealing with numbers. Aww yeah! dealwithit.png

Since images are dealt with in terms of pixels, I defined first the scaling factors (kx,ky) each axes have. I did this by getting at least three graph coordinates and its corresponding image coordinates, and compute for the scaling factors using

xi = kx * xr

Where xi is the image coordinate in x, and xr is the graph coordinate.

From here on out, it’s just a matter of getting arbitrary image pixel points on the graph
and recovering the graph coordinate using the given equation again. If you follow the same steps as I did, then you should have an image a little bit something like this…

reconstructed_graph

I did well in this activity, in my personal opinion. I can smell a crispy score of 10/10! HAHAHAH. In any case, I would like to thank Jona for accompanying me to get a sample.

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