Old Content Part 2

In any step, click the Show me link to reveal extra information. If you prefer a printout of the full set of instructions for this part, choose Print from the File menu.

Step 1 - Launch Image J and Open the First Image

  1. Launch ImageJ by selecting it from the Start Menu or by double-clicking the icon that looks like a microscope. Once ImageJ is running, the following menu and tool bar will be displayed. Opening screen of ImageJ

  2. To load the first image, select File > Open, navigate to the Forests folder, and choose image_1994.tif.
    File open menu

  3. This is what the image looks like when it opens.
    Rainforest Image 1994

Step 2 - Scale and Process the Image

In these satellite images, each pixel (picture element, the smallest unit in an image) covers a square of the Earth's surface that is just 12.5 m x 12.5 m in size. That is a lot of detailed information in one very small space. In order to make the image easier for the computer to handle, you will use ImageJ to change the resolution to 50 m x 50 m so that each pixel in the image covers more surface area.
  1. Select Image > Scale... from the menu bar and a Scale window opens. To reduce the scale by 25%, input .25 for the X Scale and .25 for the Y Scale. Check Interpolate, Create New Window, and click OK.

  2. Extract the deforested areas out of the image by applying the FFT Bandpass filters. Filter Large Structures Down to 40 pixels and Filter Small Structures up to 3 pixels. Check Autoscale After Filtering and Saturate Image When Autoscaling. Then click OK.

Step 3 - Threshold and Invert the Image

  1. Divide the forest image into two classes with the MultiThresholder plugin filter. Select Plugins > Filters > MultiThresholder. The MultiThresdholder window opens. Segment the image using the Maximum Entropy thresholding method and click Apply.
    2. The threshold is a statistical value that the MultiThresholder filter uses to divide the image in two classes. In this case, these classes approximately correspond to deforested and forested areas.
  2. For further analysis and change detection we would like to see the deforested areas in white. Select Edit > Invert. You will now see the image with forested areas in black and deforested areas (roads) in white.

Step 4 - Measure the Deforested Area

Calculate the fraction of the image that is deforested. To do that, first make sure that Area and Area Fraction are chosen in the Set Measurements window. Then choose Analyze > Measure. The Results window displays the measurements. In this case, it shows the total area of roads (in pixels) and the percent of the total area that is occupied by roads.


Step 5 - Save Your Results and Save the Image

  1. Look at the Results window and write down the percent of the area that was deforested in 1994. If you had made a series of measurements, you might want to instead choose File > Save As... to export all of your results as an Excel file. Close the Results window once you have recorded your data.
  2. Make image_1994.tif active by clicking once on it. Then choose File > Save , give this image the name, map1.tif, and save it to your Forests folder.
  3. Close map1.tif.

Step 6 - Prepare Additional Images

  1. Repeat Steps 1 to 5 above for the 1995 and 1996 image.
  2. At the end you should have three images labeled with their file names map1.tif, map2.tif, map3.tif .
  3. You should also have three measurements indicating the percent of the area that was deforested in 1994, 1995, and 1996.

Step 7 - Compare Deforestation Across All three Years

  1. What was the percent deforestation in 1994? in 1995? in 1996?
  2. How has the fraction changed through the years?
    3. Betsy, please write sample responses to these questions. Let's use the show me/hide me to provide the sample responses.