AP 186 Activity 2 Digital Scanning

      The goal of this activity is to scan a hand-drawn plot or x-y plot in a scientific journal then use the pixel locations of the data points and try to graph it on Microsoft Excel. The image in the journal was scanned in a flat-bed scanner with a resolution of 100 dpi. Here is my chosen graph:

Figure 1. Scanned graph that came from Natural and Applied Science Bulletin 40(4) Oct-Dec 1988 page 293.

            The first thing I did using GIMP was to crop the image, then rotate it. It is obvious by the figure above that the picture is not straight so it was rotated. Then, the ratio of the x-axis with respect to its pixels was calculated by measuring how long the x-axis is in pixels by using the angle tool in GIMP. Afterwards,  this number was divided by the maximum value in the axis which is 16. The same was done with the y-axis which was divided by the maximum value 120. The ratio of pixel to max value of the x-axis is 13.25 while for the y-axis it is 1.358.

The points in the graphs which are shaped like x’s, their pixel location was recorded and put into Microsoft Excel. The pixel location of the origin in the graph was also recorded. To get the x-coordinates to be used in the Microsoft Excel graph, the following equation was used:

           The calculated x_excel and y_excel points were plotted into Excel. A linear trendline was added since the graph has a linear trendlined. The image of the graph is then put as a background into the plot area. The writings on the bottom right of the picture were erased so that it will be focused on the graph. Note that the scale of the x and y points in the Excel graph are arbitrary units. I just copied the x and y axis titles of the original scanned graph.

Figure 2. Superimposed scanned image of the graph and plotted Excel graph.

               If I will grade myself, I will give myself a 10 since my graph was as near as the scanned graph points. I think I did very well and this shows that I did a good job in this activity. 

              I was very frustrated in rotating the graph because it is a hand-drawn graph, it is not really straight and I have to rotate the image at least seven times. Even if I have a grid in GIMP, there I had to pick which side will be the one that is straight. But I think I chose the best side since the resulting graph was ok and near the scanned graph.

             Thank you very much to Kat Bulan and Vyke Dominguez for helping me find the journal which I chose my graph. Thank you to Kat for answering my questions about the activity and helping me figure out what to do with my data.

Sources:

[1] Z.B. Domingo, "Cholesteric liquid crystals - the storage mode," Natural and Applied Science Bulletin  40(4) Oct-Dec 1988, 293.

[2] M. Soriano, A2 - Digital Scanning 2014 (PDF file). 2014.