A1 - Digital Scanning

Figure 1: Superimposition of hand-drawn(in black) plot and the plot of numerical values obtained(in red)

For our first activity in Applied Physics 186, we were asked to obtain the numerical values of the points on a digitally scanned hand-drawn plot.

The following are the steps that I performed to obtain the resulting plot as shown in figure 1:

1. Obtain a digitally scanned hand-drawn plot (as shown below).
resolution: 400 x 482
image type: JPEG

NOTE: to make sure that your plot is properly aligned, you can use the rotate button of GIMP 2

Figure 2: Digitally scanned hand-drawn plot

2. Using GIMP 2 erase tool to remove unnecessary points on the image.

Figure 3: cleaned image of plot

3. Open this clean image in imagej and convert it to binary image such that white pixels have the value of 255 and black pixels are represented by zero.

4. Save the XY coordinates of the black pixels by clicking Analyze -> Tools -> Save XY Coordinates buttons in imagej (these XY coordinates are in pixels)

5. To convert the pixels to numerical values, determine how many pixels make-up an actual unit value. This can be easily done by using the straight line selection button. Do this for both x and y.

6. Divide the actual unit by the number of pixels counted. This will be your conversion factor.

7. Multiply the XY coordinates obtained earlier by their respective conversion factors. The result is the actual numerical values of each point in the plot.

8. Plot. :)

Special thanks to Maam Jing for guiding me in this activity. :D

Grade: 11/10 since I was successfully able to get what is asked from the activity. I understood the concept and used my own method for some of the steps (plus 1 point).

References:
186 handout for activity 1