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The Available Bands List

Use Available Bands List to open the Available Bands List. Use the Available Bands List to access the files and the individual bands of each image file that has been opened during the current session. From the Available Bands List, display grayscale and color images, start new display windows, open new files, close files, view meta file components, and view displayed band information.

When you open a file for the first time during a session, ENVI automatically places the filename, with all of its bands listed beneath it, into the Available Bands List. If multiple files are opened, all of the files with all of the bands appear in the Available Bands List sequentially, with the most recently opened file at the top of the list. The bands of the files can be folded back into the filename to shorten the list.

To make the Available Bands List active, select Window  Available Bands List.

Figure 3-4: Available Bands List: Grayscale Band; RGB Bands

Figure 3-4: Available Bands List: Grayscale Band; RGB Bands
  

Selecting the Active Display

ENVI allows you to have multiple display groups open, with any combination of grayscale and color images displayed. When you load images, you can select an existing display or a new display to use for displaying your new images. The selected display is called the active display.

When no display group window is open, the button at the bottom of the Available Bands List reads No Display. The first image loaded automatically appears in a new window.

  1. In the Available Bands List, click the Display #n drop-down button (where n is the number corresponding to the number in a display group window's title bar) and select the display from the list.

    2.  

  2. To start a new display, select New Display from the drop-down button.

    3.  

  3. Click Load Band or Load RGB to load the selected bands into the active display.

Displaying Color Composite Images


Note
If default bands to load are set in the image header (.hdr) file, you do not need to use the Available Bands List-the color image is automatically loaded into a display group as soon as the file is opened. For details, see Setting Default Bands to Load.

  1. In the Available Bands List, select the RGB Color toggle button.

    2.  

  2. Click in sequence on the red, green, and blue bands to display (or on individual R, G, or B bands using the toggle buttons). If necessary, change the active display (see Selecting the Active Display).

    3.  

  3. When the band names are loaded into the text boxes labeled R, G, and B, click Load RGB to load the bands into the current active image display (see Selecting the Active Display).

    4.  


    Tip
    You can also load the image by double-clicking the blue bandname in the list of available bands, or by using the right-click menu (see Available Bands List Right-Click Menu).

     

    A status window displays the progress of the operation.

     


    Note
    To cancel loading the bands into a display, click Cancel in the status window. The display window is blank.

After the bands are successfully loaded, an Image window, Zoom window, and Scroll window (for large images) appears. ENVI displays all images with a default 2% linear stretch. You may change the default stretch in the envi.cfg file (see The ENVI Configuration File), or by setting a default stretch in the image header file.

Available Bands List Right-Click Menu

The Available Bands List has a right-click menu for easy access to common Available Bands List functions. For descriptions of the individual functions, see the following sections.

  1. Right-click on any filename, bandname, or map info label. The right-click menu items differ depending on which item in the Available Bands List is used to initiate the menu.

    2.  

  2. From the right-click menu, select a menu command.

    3.  

    Figure 3-5: Available Bands List: File and Band Right-Click Menus

    Figure 3-5: Available Bands List: File and Band Right-Click Menus

Editing a Header File Using the Right-Click Menu

To view or edit the header associated with a file, right-click on the filename in the Available Bands List and select Edit Header.

Editing Map Information

If a file has map information associated with it, you can view or edit this information.

To view or edit the map information associated with a file, right-click on the Map Info label in the Available Bands List and select Edit Map Information.

Displaying True Color or Color Infrared Images

If a file has wavelengths for each band stored in the header and that file contains bands in the needed wavelength ranges, you can automatically display a true color image or a color infrared image directly from the Available Bands List without having to designate the individual bands for red, green, and blue.


Note
If your data does not have bands in the needed wavelengths, the bands nearest to the wavelengths are used. This may produce a grayscale image if red, green, and blue are set to the same band.

The true color image is made by displaying the band in the red wavelength region (0.6-0.7 mm) in red, the band in the green region (0.5-0.6 mm) in green, and the band in the blue region (0.4-0.5 mm) in blue. The color infrared (CIR) image is made by displaying the band in the near infrared wavelength region (0.76-0.9 mm) in red, the band in the red region in green, and the band in the green region in blue.

To automatically display a true color or color infrared image in the current display window, right-click on a filename in the Available Bands List, then Select Load True Color to <current> or Load CIR to <current>.

To automatically display a true color or color infrared image in a new display window, right-click on a filename in the Available Bands List then select Load True Color to <new> or Load CIR to <new>.

Displaying Grayscale Images


Note
If default bands to load are set in the image header (.hdr) file, you do not need to use the Available Bands List to initiate a display - the grayscale image is automatically loaded into a display group as soon as the file is opened. For details, see Setting Default Bands to Load.

  1. In the Available Bands List, select the Grayscale toggle button.

    2.  

  2. Click on the input band name. The band name appears in a small text box labeled Selected Band.

    3.  


    Note
    If necessary, change the active display (see Selecting the Active Display).

     

  3. Click Load Band to load the band into a new or current display.

    4.  


    Tip
    You can also load the grayscale image by double-clicking the bandname.

     

    A status window displays the progress of the operation.

     


    Note
    To cancel loading the band into a display, click Cancel in the status window. The display window is blank.

After the band is successfully loaded, an Image window, Zoom window, and/or Scroll window (for large images) appears depending on your default display window style. ENVI displays all images with a default 2% linear stretch. You may change the default stretch in the envi.cfg file, or by setting a default stretch in the image header file (see Editing ENVI Headers).

Options in the Available Bands List

Use the Options menu in the Available Bands List to select a band by wavelength to display information about displayed bands, and to fold, all bands of each data set into single layers in the Available Bands List.

Locating Bands by Wavelength

For files with associated wavelength values in the file header, use the Wavelength Locator to locate the band that contains a desired wavelength.

  1. From the Available Bands List, select Options  Wavelength Locator.

    2.  

  2. When the Wavelength Locator dialog appears, enter the wavelength you want to locate and click Apply.

The band containing that wavelength is highlighted in the Available Bands List.


Note
To close the Wavelength Locator dialog, click Cancel.

Showing Displayed Band Information

To display the names and wavelengths of the bands being used in a display group:

  1. In the Available Bands List, select the display from the Display #n drop-down button.

    2.  

  2. Select Options  Show Current Displayed Bands.

The band information appears in the R, G, and B, or Selected Band (for grayscale) text boxes.

Folding Bands

In the Available Bands List and other band selection dialogs, there may be many bands listed, especially when using hyperspectral data. You can fold or hide all of the bands of a data set so that they appear on only one line. This keeps the lists shorter and easier to work with.


Note
If a band is currently displayed in either a grayscale or RGB image, an asterisk ( * ) appears next to the filename when it is folded.

Folding a Single Data Set

Data sets are loaded into the Available Bands List and other band selection dialogs in an unfolded state by default. The names of unfolded data sets appear in this format:

-<filename>
     Band
     Band

To fold a data set, click on the filename of the data set. All of the bands of the data set are compressed and the data set appears in the list in this format:

+<filename>[number of bands]

To unfold a data set and make it available for display, click the folded filename.

Folding all Data Sets

In the Available Bands List, select Options  Fold All Files, or use the right-click menu options. All of the bands of all of the data sets are compressed and each data set appears in the list in this format:

+<filename>[number of bands].

To unfold a data set, click on the folded filename.

To unfold all data sets, right click in the list of files and select Unfold All Files.

Figure 3-6: Available Bands List with Folded and Unfolded Data Files

Figure 3-6: Available Bands List with Folded and Unfolded Data Files

Managing Image Files from the Available Bands List

Use the File menu in the Available Bands List to open new image files, list open files, and close files.

Opening Files

To select a new file to open, do the following:

  1. In the Available Bands List, select File  Open Image File.

    2.  

  2. When the Enter Data Filename dialog appears, select your new file.

    3.  


    Note
    To display a list of all open files use the Available Bands List to select File  Available Files List (see The Available Files List).

Closing Files

Use Close Selected File or Close All Files to remove memory files or to close disk files from the Available Bands List.

Closing Selected Files

To close the file associated with the bands currently displayed in the Selected Band text box or in the R, G, and B text boxes, select File  Close Selected File from the Available Bands List menu; or right-click in the displayed file list and select Close Selected File.


Tip
If you close one band from a disk file, ENVI closes the entire file and all of the bands in the file disappear from the Available Bands List. However, the file still exists on disk, and you can reopen it using File  Open Image File.

Closing All Files

To close all files in the Available Bands List and delete any items in memory:

  1. Select File  Close All Files. A warning dialog appears.

    2.  


    Note
    When a memory file is deleted, there is no way to recover the image.

     

  2. In the warning dialog, click Yes.

Hiding the Available Bands List

To remove the Available Bands List from view while keeping the files it contains open and the bands available select File  Cancel.

To recall the Available Bands List at any time, select Window  Available Bands List from the ENVI main menu.

  ENVI Online Help (August 12, 2005)