Knowing the numerical values of a hand-drawn plot is a very tedious job when done manually. But with the help of technology and a bit of knowledge about image properties and a spreadsheet application, we can easily determine the numerical values of a hand-drawn plot.
To do this, the hand-drawn plot is digitally scanned (see Figure1 below) and the scanned image is used to obtain the image positions (in pixels) of desired points in the graph using Paint. The recorded positions are then plotted using OpenOffice.org Calc, but since the origin or the pixel position (0,0) is located at the top-left for images, the y-axis values are subtracted from the height of the image (in pixels) to change the origin position from top-left to lower-left in order to produce a plot similar to the image. Figure 2 shows the plot produced using OpenOffice.org Calc.
Figure1. Digitally scanned image of hand-drawn plot.
The x and y pixel values picked from the plot image obtained using Paint is shown below in Table1 while the corrected position values are shown in Table2.
Figure2. Produced plot from .
To make sure that the original hand-drawn plot was reproduced digitally, the plotted values are superimposed on the scanned plot image by making the plot image into a background of the chart produced in OpenOffice.org Calc. Figure3 shows the digitally-scanned plot with the original plot image.
Figure3. Produced digitally-scanned plot superimposed on the original plot image.
By superimposing the produced digitally-scanned plot with the original plot image we can check if the plot is reproduced successfully by digital scanning. As seen from Figure3, it can be seen that the plot is successfully reproduced meaning the values obtained by digital scanning are good approximations of the values picked from the original plot.
Figure1. Digitally scanned image of hand-drawn plot.The x and y pixel values picked from the plot image obtained using Paint is shown below in Table1 while the corrected position values are shown in Table2.
Figure2. Produced plot from .To make sure that the original hand-drawn plot was reproduced digitally, the plotted values are superimposed on the scanned plot image by making the plot image into a background of the chart produced in OpenOffice.org Calc. Figure3 shows the digitally-scanned plot with the original plot image.
Figure3. Produced digitally-scanned plot superimposed on the original plot image.I give myself a grade of 9 for this activity since the digitally-scanned plot produced approximately coincides with the original plot.
I thank Mr. Gilbert Gubatan for pointing me to an image editor for rotating and cropping the desired plot from a scanned image of a page of a book. The computer I used in the classroom did not have any image editors except paint which does not have the features I need to get an upright and exact image of the plot.
I thank Mr. Rafael Santos for sharing how to superimpose the digitally-scanned plot on the original plot image by making the original plot image a background of the produced digitally-scanned plot using OpenOffice Calc.
