Displaying Images¶
Contents
Displaying Images
At the present time, the following imagery, all TM, is stored in a Directory called “PITimages”. This contains the following scenes: 1) Morro Bay, the same image as used in Section 1 of the Tutorial; 2) Rocks, the same Waterpocket Fold scene used in Section 2; 3) Israel; and 4) NB, an image (location uncertain) in the Colorado Plateau of the U.S., illustrating a plateau type topography. Each image is 512 by 512 pixels (about 16 km or 10 miles on a side). For this training session, we will use the Israel scene, which is dominated by agriculture, with several types of crops and fields free of growing produce, along with towns, sand, and water. The scene is along the southern Israeli coast, with the town of Ashdod on the coastline. The image was acquired in August of 1985. To begin, follow these next steps to learn ways to call images into the Thumbnail window. Then, work through the subsequent instructions.
Click on Images, then Open, and the window labeled “Image path, sources, and size” comes up. Note that on the right are seven “Browse” buttons each associated with a rectangular box labeled Band 1, Band 2,….Band 7. Click on the first Browse button.
A window labeled “Select band 1 path ” appears, containing a long list of files beginning with CHANGES.LOG. You will be looking for the file “PIT images”. In the present configuration of file levels, this first list does not contain the directory named “PITimages”. Now left click on the Parent Directory button (hereafter, whenever the left button on the mouse is to be used, if the word “click” alone is used, this will mean hitting the left button just once [“double click”, which may be spelled out {or if one click doesn’t work, automatically try two clicks} requires two such actions]; if the right button is to be applied, the words “right click” will be chosen). In the next right subwindow are a list of three general directories. You should only see PIT, Rus, and Tcl. Don’t click on any of these; if you do the wrong final directory will appear. Now double click on Parent once more and a new list headed by AUTOEXEC.NU4. From the list you should now find PITimages. Click on it and a single file named “PITimages” will open. Double click on that and a list of 4 sets of TM images will appear. Hereafter, the simple direct way to get to these images is to click on Browse, then on Parent Directory 3 times which brings up the PITimage file in a list; then, just click on it to see the list.
Note: you can get to PITimages by clicking on the leftmost button, PIT, then Open, then on Parent Directory 3 times. The list reached includes “PITimages” but there is no way to connect this with the Browse routine.
First listings are the 7 TM bands labeled as ISRAEL. This scene covers an area including the town of Ashdod, about 20 miles south of Tel Aviv, a nearby military airport, and crop fields. Highlight (in blue) ISRAEL.1 by single clicking on it and click on Enter. Note that the rectangular box labeled band 1 is now filled with ./../PITimages.ISRAEL.1.
Move to the second browse button and repeat the previous (step 4) procedure which inserts ISRAEL.2. Do the same now - browse button-highlight name-enter - for those other bands as you wish to enter - in this case, all 7 TM bands for ISRAEL, which will be the image scene we will work on first in Appendix B. Be especially watchful in this sequence and make sure that the band number you want goes into its corresponding box; for TM you will confuse things if you put, say, TM 3 into Band 1 - it’s good practice to have TM and band numbers the same; if you make a mistake and put the wrong band into a box, simply hit Browse and choose the correct one - this will overwrite the erroneous one.
Go now to the Source Box and press the Browse button. A listing of Landsat sensor systems,NOAA/AVHRR, and GOES sensors will be shown. Highlight (blue) Landsat TM; then enter via the Select button. Move to the next box, Size, through Browse and pick the only choice, 512 x 512 and hit its Browse button.
Now, click on the Open button at the bottom. If you have not placed entries in all 7 available boxes, a window will replace the band entry window telling you that certain bands were not specified, and you will be asked to acknowledge this omission. After hitting Acknowledge, a large gray tone image will appear. This is the initial Thumbnail for the scene, a view of TM Band 1. Take a quick look; locate the following reference features: Mediterranean sea; docks; town of Ashdod; sand dunes; roadways; airport; active crops (darker rectangles, etc.); fallow fields (medium gray patterns).
The Image routine serves just to get the different bands online. Only one image, by default the first band, is automatically displayed. Clicking on View–>Current confirms that B1 is being displayed. You may wish to drag (on the blue banner at the top) an image to the right, as this may remove it from a screen that defaults to the left.
To see the other bands, and do some image adjustments, you must click on the View button. Then choose “Display Image Control Window”. The first thing that appears is a small window labeled: PIT - Thumbnail Image Controls. It will have three rectangular boxes, the first (top) is labeled Expression, in which B1 is entered, and the second and third, each with a sliding button, labeled Contrast and Brightness. At the bottom are four larger buttons, two of which, Apply and RGB, are of interest at this time.
Our first task is to examine each of the 7 bands. To see B2, you can proceed either by placing your cursor in the Expression box next to the 1 and delete that character with the left keyboard arrow, then type in 2 in its place and click on Apply. OR it may be easier for you to click on the black inverted triangle button to the right, which will drop down a list from B1 to B7, then clicking on B2 (or any other) and Apply. Each of the other bands is called up in the same way; but it replaces the previous band image which is lost (a way to save and display two is described later). Familiarize yourself with the appearance of each band; Band 6 is the thermal band and is rather washed out in this unstretched rendition. Look at it.
Unfortunately, this initial version of PIT does not automatically label each image by its name. To check the band number being displayed, drag the Thumbnail Control box to the right and on the image window click View, then Current, as you did for B1 earlier.
The appearance of some - maybe all - of the bands can be improved. The standard way is through some type of contrast stretch. In Section 1 on Morro Bay some of the mathematic stretches were defined and explained. PIT, as now developed, does not have these capabilities and flexibilities. It simply permits two manipulations but these lead to meaningful and esthetic results.
To learn the effective use of these sliding buttons, go back to any of the bands you wish. Let us choose Band 4 (B4). Get it displayed. Now move (holding the left mouse button down, displace the sliding button by dragging the mouse on its pad) the sliding button for Contrast all the way to the right. In the small window next to the button, a number “*8.00” should appear and the image becomes bright white after clicking Apply. Then, drag the button all the way to the left and look for “/8.00”; the image is dark (black) after clicking Apply. Once again, bring the button back to its center position. Now slide it slowly to the right. At some short distance, the number “*1.10 will suddenly appear. So, keep dragging it rightward and note that the numbers increase by units of 0.1 (leftward, the same result). Same holds for slow leftward movement. Trying the same approach using the sliding Brightness button produces a right range up to +400 and a left range to -400. Slow movement from center starts right or left increments in units of +10 and -10.
Let us do a sample stretch. Set the Contrast button at *1.50 and Brightness at +100 and then click on Apply. You will note an overall change in image gray tones, with a somewhat different range of gray levels and an overall increase in brightness. The resulting image may strike you as improved from the start - this is a rather subjective judgment. Now set the C and B limits at *250 and +200. No doubt you will react negatively to the result. Try C and B limits at /150 and - 200. This also will not be a pleasing result. For a given image, there tends to be a narrow range of C and B in combination with changed values that give satisfying improvements. You, as the analyst must pass judgment on a set of B and C values that seems to you to improve image quality - but this is obviously subjective. Note: if you move the buttons left or right only slight amounts (before any numbers appear) and then hit Apply to see any changes, nothing does change and the buttons revert to center; this means that real changes can occur only when numbers start appearing. Generally, most images improve when the C numbers fall in ranges less than *2 and /2 and B not greater than + or - 150 but some processing operations yield new images that require more extensive stretches or overall tone increase/decrease, so that the larger values apply. While you are at it, try to find the best stretch that optimizes band 6 gray levels.
Images in color are the next set of products sought through image processing. PIT makes these in a straightforward way. To start, again click on View and then Display Image Control Window. As before, the Thumbnail Image Control window will come up, as it does for individual band stretches. But, now click on the RGB button, and a new larger window comes up with three internal rectangular boxes, the top outlined in red, the middle in green, and the bottom in blue. Each one also has a pair of C and B sliding buttons. Note that, by default, B1 is inserted in each of the three Expression boxes. Also, there are Gray and Palette buttons to the right. Do not use the Palette button at this time. If you want to see any individual band image, press on Gray which will bring up any individual band you enter in the usual way. A stretch may be needed.
To see an image in color, choose what band you wish to render in the particular color you select, either by accepting or editing the band number in the Expression box or clicking on the black triangle and selecting the Bn desired. As an example, put B4 in the red Expression box, B3 in green, and B2 in blue. Then press Apply. A standard false color composite, with vegetation in red, should replace the band 3 image. Next, either delete/type the number or use the triangle, put B3, B2, and B1 in the red, green and blue outlined boxes. This will give a good natural color view.
But, better renditions are possible, even likely. Move experimentally the sliding buttons for each of the three bands to new positions, followed by Apply. Keep doing this until you reach a color display that seems close to nature or is at least esthetic. One natural view that is pleasing is B3: *1.10, +30; B2 *1.80, +30; B1 *1.10, +10. In effect, you are enhancing the image by selective, band by band, contrast stretching.
For the fun and knowledge of it, try other combinations, as you choose. For example, R = B7, G = B2, B = B4. Various subtle new information may emerge from some particular combination. Also, vary C and B. Remember to enter through Apply.
PIT has a systematic size changing program, or Zoom, that enlarges or diminishes an image. To bring about a change, follow this sequence (which also previews a major operation which we will do under the Classification tutorial): From the PIT Thumbnail window (hereafter, alternately just referred to as the PIT window), click on the rightmost button, Windows, then through these choices in the step windows that will appear to the right = Open - Interpretation - Scheme (top or left). After the left mouse button is released at the last step, a large window will appear with a black rectangle on the left (or top; depending on choice) and an image will appear in a window to its right.That image is the current one that is active. If you prefer to display another band, press on View, click on Display Image Control Window, then change band number in the Expression box (or click on RGC and fill in all three to get a color composite), and hit Apply. Note that the image that you settle on will have a square grid superposed on it (this grid is used in the classification procedure). To remove this grid for now, go to View, then click on Show and note that four options are listed. One is labeled Grid and has a check mark in front. Click on the check mark, which removes it, and then displays the image without the grid. You are now ready to Zoom.
The procedure to change size is simple. Assuming you are still in the PIT-Interpretation window, first, click on View, then on Zoom in its dropdown menu. This will display numbers like 2x, 4x, 8x, … . Whichever has the check in front denotes the size increment that will take place one step at a time. Most instances, an increase by 2x is adequate, but the higher numbers enlarge or diminish the image by greater amounts. For now, choose 2x. Then, click on Mode (top left button), and in its window menu will be two options: Zoom In (enlarges) and Zoom Out (diminishes). Assuming you have a full scene in display, choose the Zoom In command. Nothing apparently happens but move your mouse to bring the cursor into the image. You should see that the cursor has changed to a small bright square outline with a dot in its middle. Place that square somewhere in the image where you seek enlargement and click once (left). A new scene shows up in the image window, which you should recognize as a part of the image surrounding the square at its center. If you want to see a different area enlarged, repeat the procedure with the cursor placed within it. Or, given the first enlargement, center the square and click again. Once more, the expansion is by a factor of 2x; the image now begins to show individual pixels (as squares) but recognizable features may still retain identifying patterns. Repeating this once more (now 2x three times, or 8x) makes the pixels so large that the patterns begin to break down. To reverse the size increase, go to Mode, then Zoom Out, by clicking on that command. The cursor, when it is placed somewhere on the (restored or enlarged) image, has a different shape: it is a cross (+) with the tips ending in tiny arrowheads. Depending on the degree of enlargement, one or more clicks will in effect increase the displayed pixel size while restoring the image scene to larger scene areas that are displayed. From 8x, three clicks will restore the original full scene, if that was the starting point. Enlargements by zooming in provide smaller subsections of a scene that may be all you will wish to classify or otherwise manipulate. Note: you can start with a higher zoom factor, e.g., 4x or 8x, cutting out incremental steps.
PIT presently is not designed to routinely display more than one image band at a time but there is a way to put most of the areas of two bands on the screen simultaneously. To do this, first put up the PIT Thumbnail image (after closing out the PIT - Interpretation window by hitting on its X button) and if other than the default image is to be displayed, get it in the usual manner through View - Display Image Control Window and select the band (delete/place number or black triangle) wanted + Apply. After it is then displayed, you next want to bring up the second band. To do this, at the top click and drag on Windows - Open - Classification - Supervised - Image - Partial - Top Scheme, and click the mouse button on that last command. Either a blank pair of windows will come up or the bottom window will have the image of one of the bands (check Current). To get the band you want in this right window, go to View - Display Image Control Window - band number - Apply. You should now see both band images but a small part of one and/or the other may not be visible. You can move either or both around the screen by placing the cursor on the top banner, holding the mouse button down and dragging. Keep in mind, also, that there are other situations in using PIT where windows might overlap; in some instances these can be repositioned by dragging one or more, again by placing the cursor on the blue title bar (top). Note: Using top schemes and 1280 x 1024 screen resolution will allow the windows to be viewed side-by-side with no overlap.
Now that you have completed these first processing operations using PIT, the primary writer (NMS) wants to call your attention to several pitfalls that could be encountered using the present version of PIT (which implies it hasn’t been sufficiently debugged). First, like most programs it can shut down erratically, when certain actions are taken. If that happens, you will need to start over. Second, it is sometimes difficult to switch from one operation to another. There is no Back or Undo buttons. In some cases, simply hitting the minimize button (-) will get a current program off screen, permitting the user to access a previous screen or program (check the bottom of your desktop for buttons that show the removed program can still be re-activated. Sometimes, the Esc(ape) button on your keyboard will remove a window. Finally, just clicking in the desktop background can perform a desired action. Third, there are certain commands or action in the original write-up by Jeff Love that are not correct. For example, “Enter” in his instructions for some operations is not correct - this does not mean hitting your keyboard Enter. Instead, Open or Apply should be the choice. NMS has tried to change these as he reviewed and revised these Instructions, but one or more of this command may have been missed. If you, the user, find inconsistencies or confusing or downright incorrect instructions (for instance, flaws in a sequence) email NMS.