Activity Title: “Calculating the Volume of Objects Using Their Pictures”
Introduction
ImageJ is a photo editing program that can be used to alter, measure and analyze photographs. This lab utilizes ImageJ’s photo analytics to investigate elements of digital photographs. These tools can be used to calculate lengths, areas, volumes and angles. We will use these tools to calculate the volume of a container and estimate the number of pieces of candy that will fit into it.
In this lab, students will use ImageJ to calculate the volume of a piece of candy and the volume of the container that holds some number of pieces of candy. How many pieces of candy will fit into the container? The winning team of students will receive a prize!
Materials List:
· Computer loaded with ImageJ software
· Rectangular prism containers
· Rectangular prism candy (or other object)
Procedure
Background:
You should have some experience with calculating volumes of three dimensional solids. ImageJ is like many picture editing programs, but you may want to research the program before you start. Take a look at the following YouTube video, you may want to jump to the time of 3:18, where the instruction begins.
http://www.youtube.com/watch?v=YXo2zDJ6kN4
Preparation: Provide students with computers loaded with ImageJ software, rulers, rectangular prism container and candy. Make sure that at least one student in each group has a smart phone with camera.
Lab Activity:
Step 1 - Loading Photos
ImageJ’s menu has several options: File, Edit, Image, Process, Analyze, Plugins, Window and Help. The File, Edit and Help menus are the same as in any program, such as Microsoft Word. The Image menu is used to alter visual values of a photograph, like brightness, zoom or cropping. The Process and Plugins menus include filters that can enhance the quality of a picture. Analyze helps you to measure things within the subject of the picture and Window allows you to manage your viewing windows when using many photographs, as seen in Figure 1.
Figure 1 – An example object
To open a picture file, use the File menu and find open. Locate the file you wish to open and select it. The picture you selected should appear in a new window. Note that ImageJ can only open certain file formats. Click the link below to see them. http://imagejdocu.tudor.lu/doku.php?id=faq:general:which_file_formats_are_supported_by_imagej
Step 2 – Setting the Measurement Scale
You can use ImageJ’s Analyze menu to measure objects within your photo. Before you do this you must determine a scale for your photograph. To create a scale for your photograph, there must be an object that you know the length of in the picture; for example a ruler, tile, standard piece of paper or other object. Mark a known length on your ruler with the Line Segment Tool, as seen in Figure 2, by clicking and dragging along the object. Once you have a line segment fitted to your know length, access the Analyze Menu and select Measure. A new window will pop up; focus on the length column. This length is given in pixel length, but must be converted to centimeters, inches, etc. – based on the measurement scale on the ruler.
Figure 2 – Measurement screen in ImageJ
To set your scale, divide your pixel length by your known length to get a pixel per unit conversion. You can also do this by accessing the Analyze Menu and selecting the set scale option, as seen in Figure 3. Type in your known length and units of measure and ImageJ will do the rest for you! Now, next time you take a length measurement, it will be measured in your desired units. Find the length, width and height of your container and piece of candy.
Figure 3 – Scale screen in ImageJ
Step 3 – Calculating Volume
You should now calculate the volume of your container and piece of candy using the measurements you have made. Determine how many times larger your container is than your piece of candy. How does this relate to the candy capacity of the container? What is your final answer to how many pieces of candy fit into the container? Compare your results with real life!
Assessment
Pre-Assessment:
1. Estimate the volume of the container.
2. Estimate how many pieces of candy will fit into a given container.
Results/Conclusions:
1. How do you calculate the volume of three dimensional figures?
2. Can you determine the ratio of volumes of figures with and without ImageJ?
Reference(s):
Appalachian State University’s 2013 RET module experiments.