Density Slicing
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It is relatively easy to determine the area of an irregularly shaped object if there is good contrast between that object and its background
Density Slicing is a technique that can be used with images taken from the WEB, photographed in class, laboratory or in connection with some particular project. It allows the investigator to calculate the surface area of almost anything from a landsat photograph to the shells on the right.
Show ImageJ application.
Go to File, Open Samples and open image Shell. This is a view of three shells that were photographed with a ruler. Having a ruler in any image makes it possible to calibrate the image. Before we can measure we have to change the image to a an grayscale image. Go up to Image, Type and check 8-bit Grayscale.
There is a ruler that measures in inches on the top and cm. on the bottom. Use your magnifier and click between 4 and 5cm. on the bottom scale. This will enlarge your view. (To go back hold down the Option key and click) Take your straight line
tool and click on the 4 cm. left side of this scale and draw the line to the 5 cm. Go up to Analyze, and click on Measure. (You should get a reading of around 28 which is in pixels) Now go to Analyze, Set Measurements and the only boxes selected should be area, perimeter and Limit to Threshold. Click OK and then go to Analyze, Set Scale. (It is 28 in the example given) Enter the distance in pixels that you got, and then enter 10 for known distance as 10 millimeters (1 cm.). Click OK
Density Slicing
Tool and click next to the area you want to measure. You will see a yellow line surrounding all the red. Now do Analyze, Measure. The area of everything that you have selected in RED has been measured in pixels unless you have already calibrated the image.
Put your answers in the Results Section.
Results:(You can also Go to File, Open Samples and Open the image Results which is a copy of this Results section. While this page cannot be printed out - at this time - it can be saved as a JPEG file to your desktop. You can then open it with any graphics program,type out the answers and then print it out from your program.
You can also enter the results on this image using the Text
Tool. To do this first go to Edit, Options, Fonts and select something like Geneva - 12 pt - Bold. Then click on the Results Image in the answer space and draw out the yellow rectangle that appears and start typing. When you are finished go to Edit and Select Draw. What you have typed should now be present.)
1. Complete the results chart shown below.Shell Area
2. What other objects, they do not have to be biological, can you see using this method of analysis with?
