Lab - Introduction to ERDAS IMAGINE I

The goals for you to aim for in this lab:

• Build simple and compound database queries
• Extract the results of a query into separate GIS layers
• Count the number of features within the boundary of another feature
• Overlay two features for spatial analysis
• Create and use buffers around objects for spatial analysis

Outline:

Materials (click to download)

Contrast Stretching • Improving detectability of objects by increasing the variation of tones • Redistribution of DNs along the bit scale to utilize more of the gray scale • Original range of DNs expanded to utilize a fuller contrast range of display device

ContrastStrech.png • Many times DNs don’t occupy the full range o Example: DNs = 40, 45, 50 o All look dark gray because they are so close on the 255 range o Contrast stretching temporarily contrasts the numbers; doesn’t corrupt original values  40 assigned 0  45 assigned 127  50 assigned 255  end up with 1/3 black, 1/3 gray, & 1/3 white

ERDAS IMAGINE • when displaying image in IMAGINE, we can specify which bands we want to display with which color gun (Red, Green, Blue) o Example: SPOT Band 2 (red) can be displayed with green color gun • What the computer assigns Layer 1 may not correspond to Band # o Example: Layer 1 in SPOT image may not be SPOT Band 1

Step 1: Copy files to your directory Log on to the machine. Go to your directory and create a Lab04 folder. Right click on the Lab04 folder and choose copy. Navigate to the folder that you just created, right click and choose paste.

Step 2: Accessing ERDAS IMAGINE Click on the Start button and search ERDAS Imagine 2014. After a moment the IMAGINE logo should come up, there may be license expiration information, click “Continue”. Followed by the main IMAGINE menu, a panel across the top of the computer screen. A “viewer”, a black screen in which images are displayed, should also come up. You can resize these windows by grabbing the corners of the windows with your cursor, or you can move the windows around if you so desire.

Step 3: Displaying an Image To display an image, right click on “2D View #1” under the contents menu on the left side of the screen and click on “Open Raster Layer…”, or simply click on the open file icon at the very top left of the screen. The Select Layer to Add window should now appear. Select your personal folder from the “Look in:” dropdown menu. In your directory, select (highlight) the file garden.img, but don’t click OK just yet. The data in this file are from a subset of SPOT’s multi-spectral sensor over western Kansas near Garden City. Look at the other information in the Select Layer to Add window under the Raster Options tab. The Display as should be on True Color. Switch back to the File tab. At the very bottom is additional information, including the number of columns and rows and the number of bands in the image.

1. How many bands are available? What are the wavelengths represented by Spot’s Multi-spectral Scanner (XS) sensor (provide the band number, name, and wavelength)? (4 points) Use your textbook for this question.

Band Wave Length Name

After answering the above questions, click OK. Once the image is displayed, you can retrieve information regarding various characteristics of the layer by clicking on the Metadata icon under the Home tab (the icon looks like a piece of paper with an “i” in the center). After the Metadata dialogue box opens (this may take a bit!) click on the General tab and find the Layer Info data box, in this look at the Height and Width numbers.

2. How many columns of data do we have? __________ Rows?_____________ (2 points)

Step 4: Assigning Color Guns to Bands Reopen garden.img. Under the heading “Layers to Colors” on the Raster Options tab of the Open Raster Layer window, we can specify which computer color gun is used to display a certain band. Change it to Red-1, Green-2, and Blue-3.

This is telling you that we are assigning band 1 to the first “color gun”, which is red; band 2 to the second color gun, which is green; and band 3 to the third computer color gun, which is blue. If you entered layers (or bands) 3,2,1 in that order, it would assign band 3 to color gun 1 (red), band 2 to color gun 2 (green), and band 1 to color gun 3 (blue). Get it? You can change the assignment of bands to color guns by clicking on the Multispectral tab and go to Bands where you will see the three color guns to assign.

In the bottom of the same window, check Clear Display(this clears the data from the display window). Also click on the box Fit to Frame- you’ll want to do this every time you display an image. This displays the whole image in the window, rather than setting it to a pre-defined default zoom. Now click OK at the side of the screen. The Spot image should appear, covering an area of about 6 sections by 6 sections (generally, 4 center pivot plots cover a whole section).

Keep in mind that these data have been “contrast stretched” to make it easier to interpret visually. This is done by the computer’s examination of a statistics file of the image to determine how it should be stretched. You will learn how to do this later.

3. The image displayed is a color composite. What type of color composite is it? (1 point)

4. Suppose we assigned band 3 to all color guns, what will this image look like? And WHY? (Explain why this image displays in this color scheme - remember that all three colors were assigned the same band of data). (3 points) Will it be a color composite or…?

Step 5: SPOT Image Change the band combinations on the image, i.e. change the band-color gun assignments. On the main menu, click the Multispectral tab. Here there is a sub-menu called “Bands”. Change the band assignments to 3 to red, 3 to green, and 3 to blue. In effect, we are only displaying one band of the data,.

Look at the image.

Keep in mind that the bands of SPOT may or may not have been entered in the correct order. To investigate pixel values and the DN’s associated with them, press the Inquire “+” icon on the viewer menu under the Home tab. This brings up the “inquire cursor”. In the window that now comes up, examine the file File-pixel column. These are the reflectance values (PV’s, DN’s, etc.) for the pixel on which the cross-hairs of the cursor lie. You will see pixel values for each of the layers of your image. Move around the cursor with your mouse and watch the pixel values change. This should help you interpret which of the image layers actually correspond to which SPOT bands.

5. What is the SPOT wavelength that is represented by this image (be careful!!)? (1 point) (Come back to this later if you don’t know)

6. Look at the SPOT bands one at a time (by using Multispectral tab/Bands subtab and assigning a band to all color guns), considering how the composite image looked in question #3 and the color assignment information.

Go back and look at the composite you used in #3-4 (bands 1,2,3 assigned to RGB color guns, respectively)

Are the SPOT bands in their proper order? (is band 1 really the first band of SPOT data? In other words, is this really the shortest wavelength band of SPOT?). [HINT: Use the “inquire cursor”, examine pixel values, assume all center-pivots in the lower right are vegetated. Justify your answer and, if they are not in correct order, what order are they in? (3 points) Please see next page.

   Are they in Proper order:  YES             NO
   Indicate order: Band

1 =
2 = 3 =

Step 7: MSS Image Let’s display another image. You can continue using the same viewer if you wish. Or, if you want to keep the garden.img up, you can open another viewer window, by clicking on the File tab, then click on the New option, and then click on the 2D View option (Do not worry about the additional options that appear).

Use the open file button and find msslaw.img in your directory. Accept the default color assignments, but in Raster Options tab, click on Fit-to-Frame. Click OK

7. This image is a Landsat MSS image of Lawrence. Comment on the spatial resolution with respect to garden.img. (2 points) Is the spatial resolution coarser or finer?

8. Both the garden.img and msslaw.img are subsets (smaller portions) of the full SPOT and MSS scenes. Assume both subsets are same % of the total image. However, if both a full SPOT image and a full MSS image were displayed to the same dimensions, which would be smaller-scale and why? (3 points) Which full scene will cover the largest area?

TM Image Now, let’s display a TM image. In a viewer window, click on the open file to display tmdata.img (the one saved in your directory) as a single band gray-scale image. This file contains TM data over Lawrence. Let’s simply examine each band individually. This time, in the Open Raster Layer window, under Raster Options tab, find the Display As field and from the dropdown menu select Gray Scale, and select band (layer) 1. Before displaying it, answer the following:

9. Under Layers, how many bands (layers) are available? ___________________ (1 point)

As I mentioned, IMAGINE performs an automatic contrast stretch. However, let’s take a look at what happens when we do not perform a contrast stretch. Under Raster Options, click on Fit-to-Frame and No Stretch. Click on OK.

You should be displaying only band 1 (without contrast stretching).

10. Suppose we had chosen the True Color display option and assigned band 1 to all three color guns, what color would the image be displayed as? (see #4) (1 point)

Look at the displayed image. Note that these data have not been contrast stretched! These are RAW data, with each pixel assigned a computer brightness value that matches their pixel value.

11. Are all the land cover types clearly distinct from one another? (2 points)

12. Which 3 land cover types have a higher spectral reflectance? (2 points) They are lighter/brighter in the image.

Use the Panchromatic tab and examine each band individually (remember to click on Fit-to-Frame). Continue to do this until you have looked at each band (1-7). Close the Set Layer Combinations window when done.(Note: there is a drop down menu and each band is there)

Redisplay the tmdata.img by using the open file and assign band 1 to all the color guns (again, using True Color and Fit-to-Frame, but this time do not click on the No Stretch box).

13. In what 2 ways is this image display different from the non-stretched one? (3 points)

Again, use the Multispectral tab  Bands subtab to look individually at all the bands, now in contrast-stretched form.

14. Which band is the Thermal band? How can you tell? (2 points) It should be obvious which one looks different. Look at your textbook for a description of how the thermal band differs.

The bands 1-7 of tmdata.img match Landsat TM bands 1-7. Next you are going to display a color-IR false color composite, a digital image which mimics a Color Infrared photograph.

Redisplay the image tmdata.img with the open file. Use True Color as the display, and for the color gun assignments, use 4,3,2, in that order. Also, let’s see what the image looks like without contrast stretching. Click on the No Stretch box and Fit-to-frame, then click on OK.

15. Provide Band #, wavelength and word description for band-color gun assignments.(9 points) Look at your textbook for the information on the bands you displayed.

                Band #		   Wavelength		Color Gun Assignment
    

Red color gun will display ______ _____________ ___________________

Green color gun will display ______ _____________ ___________________

Blue color gun will display ______ _____________ ___________________

This image lacks contrast (as did the single band “no stretch” images) because we did not let IMAGINE perform the automatic contrast stretching. Let’s try to manually change contrast. In the contents tab on the left, right-click on the current image and select Brightness/Contrast. Use the HELP button to find out what the two top slide bars refer to. Press File-Exit to close the help window. The contrast and brightness can also be found under the Multispectral tab

Top slide bar refers to: (1 point)

Bottom slide bar refers to: (1 point)

16. Change brightness to 60 and contrast to 75. Click Apply. How does this change the image? (2 points)

Play around some more with the contrast tool. Alter the slider bar values. When you want to go back to the original image, just hit Reset. Just make sure you DO NOT hit SAVE on the Contrast Tool menu – this will permanently change the file. Hit Close to exit from the Contrast Tool window.

Use open file to redisplay the same 4,3,2 color composite of tmdata.img, only this time do not click on the No-Stretch box. Let IMAGINE perform its automatic contrast stretching.

After you have looked at the automatic contrast-stretched image, go to the Multispectral tab\Bands subtab to alter the band combinations of tmdata.img. Change color gun assignments to 3,2,1, red, green, blue (RGB) respectively. 17. What type of color composite is this? (Hint: Think theoretically what you are doing - what wavelengths are you assigning to which color guns?) (1 point)

Play around with other band combinations to form different color composites if you wish. When you are finished, press File  Exit from the main IMAGINE panel menu. If you get the following prompts, “Are you Sure you want to quit Imagine?” YES, and “Do you want to print the log file?” NO. YOU’RE DONE!!!!!!

All you have to turn into blackboard for this week is the final image you created above.