ENVI Tutorial
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ENVI Tutorial: A Quick Startto ENVIA Quick Start to ENVI 2Files Used in this Tutorial 2Getting Started with ENVI 3Starting ENVI 3Loading a Gray Scale Image 3Familiarizing Yourself with the ENVI Interface 5ENVI Main Menu Bar 5Right-Click Menus 6The Image Window 6The Zoom Window 7The Scroll Window 9Applying a Contrast Stretch 10Applying a Color Map 11Animating Your Image 12Using Scatter Plots and Regions of Interest 13Loading an RGB Image 14Classifying an Image 15Dynamically Overlaying Images 16Overlaying and Working with Vectors 171ENVI Tutorial: A Quick Start to ENVIA Quick Start to ENVIThis Quick Start tutorial is aimed at providing a newer ENVI user with a brief introduction to thegraphical user interface and basic capabilities of ENVI.Files Used in this TutorialENVI Resource DVD: D a t a \ c a n _ t mF i l e D e s c r i p t i o nc a n _ t m r . i m g Cañon City, CO, TM Datac a n _ t m r . h d r ENVI header for abovec a n _ v 1 . e v f ENVI vector file 1c a n _ v 2 . e v f ENVI vector file 2c a n _ v 3 . e v f ENVI vector file 3c a n _ v 4 . e v f ENVI vector file 42ENVI Tutorial: A Quick Start to ENVIGetting Started with ENVIBefore attempting to start the program, ensure that ENVI is properly installed as described in theInstallation Guide that shipped with your software.Starting ENVIWindows:Select S t a r t > P r o g r a m s > E N V I x . x > E N V I. (where x.x is the ENVI version number)Unix:For ENVI, enter e n v i _ r t ...
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ENVI Tutorial: A to ENVI
A Quick Start to ENVI Files Used in this Tutorial Getting Started with ENVI Starting ENVI Loading a Gray Scale Image Familiarizing Yourself with the ENVI Interface ENVI Main Menu Bar Right-Click Menus The Image Window The Zoom Window The Scroll Window Applying a Contrast Stretch Applying a Color Map Animating Your Image Using Scatter Plots and Regions of Interest Loading an RGB Image Classifying an Image Dynamically Overlaying Images Overlaying and Working with Vectors
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Quick Start
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ENVI Tutorial: A Quick Start to ENVI
A Quick Start to ENVI
This Quick Start tutorial is aimed at providing a newer ENVI user with a brief introduction to the graphical user interface and basic capabilities of ENVI.
Files Used in this Tutorial _ ENVI Resource DVD: Data\can tm
File can tmr.img _ can tmr.hdr _ _ can v1.evf _ can v2.evf can v3.evf _ can v4.evf _
Description Cañon City, CO, TM Data ENVI header for above ENVI vector file 1 ENVI vector file 2 ENVI vector file 3 ENVI vector file 4
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ENVI Tutorial: A Quick Start to ENVI
Getting Started with ENVI Before attempting to start the program, ensure that ENVI is properly installed as described in the Installation Guide that shipped with your software. Starting ENVI Windows: Select Start > Programs > ENVI x.x > ENVI . (where x.x is the ENVI version number) Unix: _ For ENVI, enter envi rt at the UNIX command line. For ENVI+IDL, enter envi at the UNIX command line. Macintosh: First, display an OSX, UNIX X-window. For ENVI, type envi rt at the UNIX command prompt. For _ ENVI +IDL, type envi at the UNIX command prompt. Loading a Gray Scale Image Open a multispectral Landsat Thematic Mapper (TM) data file representing Cañon City, Colorado, USA. Opening an Image File 1. From the ENVI main menu bar, select File > Open Image File . 2. Navigate to the Data\can tm directory, select the file can tmr.img from the list, and click _ _ Open . The Available Bands List dialog appears on your screen. This list allows you to select spectral bands for display and processing. You have the choice of loading either a grayscale or an RGB color image.
3. Select TM Band 4 . The band you have chosen is displayed in the field marked Selected Band.
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ENVI Tutorial: A Quick Start to ENVI
4.
Click Band
the Gray Scale radio button then click Load 4 will be loaded as a gray scale image.
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Band
to
load
the
image
into
a
new
display.
ENVI Tutorial: A Quick Start to ENVI
Familiarizing Yourself with the ENVI Interface When the image loads, an ENVI image display appears on your screen. The display group consists of an Image window, a Scroll window, and a Zoom window. These three windows are intimately linked; changes to one window are mirrored in the others.
You can choose which combinations of windows appear on the screen by right-clicking on any display group window to display the right-click menu and selecting a style from the Display Window Style submenu. Use the ENVI main menu bar File > Preferences > Display Defaults tab to change the default settings for which windows you wish to display and where you wish to position them. All windows can be resized by grabbing and dragging a window corner with the left mouse button. 1. Resize the Image window to be as large as possible (until the Scroll window disappears). 2. Now, make the Image window smaller than the full extent of the image data (the Scroll window will reappear). 3. Resize the Zoom window and notice how the outlining box changes in the Image window. ENVI Main Menu Bar In ENVI, activities are initiated by using the menus in the ENVI main menu bar, which may be oriented horizontally as shown below, or vertically (as set via the option on the File > Preferences > Miscellaneous tab).
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ENVI Tutorial: A Quick Start to ENVI
Right-Click Menus Each of the three display windows has a right-click menu for accessing general display settings and some interactive functions. Access this menu by right-clicking in the window.
The Image Window The Image window shows a portion of the image at full resolution.
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ENVI Tutorial: A Quick Start to ENVI
The Display Group Menu Bar The menu bar in the display group provides access to many ENVI features related to the images in the display group. This menu appears at the top of the Image window by default. If you have chosen to display only the Scroll and Zoom windows or just the Zoom window, the menu bar will appear at the top of the Zoom window. The Image Window Zoom Box The Zoom box (the colored box in the Image window) indicates the region that is displayed in the Zoom window. 1. Place the mouse cursor in the Zoom box in the Image window, hold down the left mouse button, and move the mouse. The Zoom window is updated automatically when the mouse button is released. 2. Place the cursor anywhere in the Image window (outside of the Zoom box) and click the left mouse button to move the magnified area instantly. If you click, hold, and drag the left mouse button in this fashion, the Zoom window is updated as you drag. 3. Click once in the Zoom box in the Image window and use the arrow keys on your keyboard to move the box. To move several pixels at a time, hold down the Shift key while using the arrow keys. Scroll Bars You can choose to have scroll bars displayed in the Image window. These scroll bars provide a way to move through the Scroll window, allowing you to select which portion of the image appears in the Image window. 1. Right-click in the Image window and select Toggle > Display Scroll Bars . 2. To have scroll bars appear in the Image window by default, use the ENVI main menu bar to select the File > Preferences > Display Defaults tab. Set the Image Window Scroll Bars toggle to Yes . The Zoom Window The Zoom window shows a portion of the image magnified the number of times indicated by the number shown in parentheses in the Title Bar of the window. The zoom area is indicated by a highlighted box (the Zoom box) in the Image window.
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ENVI Tutorial: A Quick Start to ENVI
There are three Zoom controls (red by default) in the lower left corner of the Zoom window. These control the zoom factor and the crosshair cursor in both the Zoom and Image windows. 1. Place the mouse cursor in the Zoom window and click the left mouse button to reposition the magnified area (displayed in the Zoom box in the Image window) by centering the zoomed area on the selected pixel. 2. Click and hold the left mouse button in the Zoom window while dragging. This causes the Zoom window to pan within the Image window. 3. Click the left mouse button on the graphic in the lower left corner of the Zoom window to zoom out by a factor of 1. 4. Using a three button mouse, click the middle mouse button on the graphic to zoom out by a factor of 2. 5. Click the right mouse button on the graphic to return the Zoom window to the default zoom factor. 6. Click the left mouse button on the graphic to zoom in by a factor of 1. 7. Click the middle mouse button on the graphic to zoom in by a factor of 2. 8. Click the right mouse button on the graphic to return the Zoom window to the default zoom factor. 9. Click the left mouse button on the graphic to toggle the crosshair cursor in the Zoom window on or off. 10. Click the middle mouse button on the graphic to toggle the crosshair cursor in the Image window on or off. 11. Click the right mouse button on the graphic to toggle the Zoom box in the Image window on or off. 12. The Zoom window can also have optional scroll bars, which provide an alternate method for moving through the Zoom window. Right-click in the Zoom window and select Toggle > Zoom Scroll Bars . To have scroll bars appear on the Zoom window by default, use the ENVI main
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ENVI Tutorial: A Quick Start to ENVI
menu bar to select the File > Preferences > Display Defaults tab. Set the Zoom window Scroll Bars toggle to Yes . The Scroll Window The Scroll window displays the entire image at reduced resolution (subsampled). The subsampling factor is listed in parentheses in the window Title Bar at the top of the image. The highlighted Image box (red by default) indicates the area shown at full resolution in the Image window.
1. Place the mouse cursor inside the Image box, hold down the left mouse button, drag to the desired location, and release to reposition the portion of the image shown in the Image window. The Image window is updated automatically when the mouse button is released. 2. Click anywhere within the Scroll window using the left mouse button to instantly move the selected Image window area. If you click, hold, and drag the left mouse button in this fashion, the Image window will be updated as you drag (the speed depends on your computer resources). 3. Click in the Image box and press the arrow keys on your keyboard. To move the image in larger increments, hold down the Shift key while using the arrow keys.
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ENVI Tutorial: A Quick Start to ENVI
Applying a Contrast Stretch
By default, ENVI displays images with a 2% linear contrast stretch. You can choose to apply a different contrast stretch. 1. From the Display group menu bar, select Enhance to display a list of six default stretching options for each of the windows in the display group (Image, Zoom, Scroll). 2. Select an item from the list (for example, Enhance > [Image] Equalization to apply a histogram equalization contrast stretch to the Image window). This action also updates the Scroll and Zoom windows in the display group. Try applying several of the different available stretches. 3. Alternatively, you can define your contrast stretch interactively by selecting Enhance > Interactive Stretching from the Display group menu bar.
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ENVI Tutorial: A Quick Start to ENVI
Applying a Color Map By default, ENVI displays images using a grayscale color table. You can apply a pre-defined color table to an image or select a color table from a list. 1. From the Display group menu bar, select Tools > Color Mapping > ENVI Color Tables to display the ENVI Color Tables dialog.
2. Select a color table from the list at the bottom of the dialog to change the color mapping for the three windows in the display group. 3. In the ENVI Color Tables dialog, Auto Apply is selected by default ( Options > Auto Apply ), so the color table will automatically be applied. You can toggle this feature on or off using this menu option. If Auto Apply is off, you must select Options > Apply each time you wish to apply the color table and observe the results. 4. From the ENVI Color Tables menu bar, select Options > Reset Color Table to return the display group to the default grayscale color mapping. 5. From the ENVI Color Tables menu bar, select File > Cancel to dismiss the dialog.
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