ENVI Image Windows

When you display an image file, it is placed in an ENVI image display group, which consists of an Image window, a Zoom window, and/or a Scroll window (Scroll windows for larger images only). The windows included in the default display group are controlled by the Display Window Style option in the preferences. Multiple image display groups can be on the screen at once, but only one display group is active (see Selecting the Active Display).

The Image Window

The Image window displays a portion of an image at full resolution. The window is automatically created the first time you open an image.

In an Image window or from the ENVI main menu, select Window

Start New Display.

In the Available Bands List, click New Display (see Selecting the Active Display).

Figure 3-7: Image Window for Display #1 with Zoom Box

Figure 3-7: Image Window for Display #1 with Zoom Box

Resizing the Image Window

Dynamically resize the Image window up to available screen size by grabbing one of the corners and dragging to the desired image size.

From the Image window menu bar, select File

Preferences and enter the size in the Display Defaults dialog (see Resizing Windows).

Change the default window size parameters set in the envi.cfg configuration file (see Customizing ENVI).

Displaying Image Window Scroll Bars

Use the scroll bars in the border of the Image window to move around the image. When you move the scroll bars, the graphic box in the Scroll window moves to show you what part of the whole image you are in. There are three ways to display the Image window scroll bars:

Displaying Scroll Bars at all Times

Select File

Preferences.

In the Edit System Preferences window, select the Display Defaults tab. The Preferences: Display Defaults dialog appears.

Click the Image Window Scroll Bars arrow toggle button to select Yes.

Click OK.

In the Edit System Preferences window, select File

Save Configuration.

Note
To exit without saving, select File

Cancel.

Enter an output filename and click OK.

Turning Display Scroll Bars On/Off

Right-click in the Image window and select Toggle

Display Scroll Bars or from the Image window menu bar, select File

Preferences. The Display Preferences dialog appears.

In the Image Window section of the dialog, click the Scroll Bars arrow toggle button to select Yes or No.

Click OK.

Controlling the Zoom Window from the Image Window

In the Image window, the Zoom box outlines the area that displays in the associated Zoom window.

To change the region defined by the Zoom box, click-and-drag that box around in the Image window.

Use the arrow keys on the keyboard to move the Zoom window pixel-by-pixel in the direction of the arrow. Use Shift + arrow to move the Image window five pixels in the direction of the arrow.

Note
Some interactive processes change the mouse functions listed in the following table. These processes include defining Regions-Of-Interest (ROIs), Annotation, Vector Overlay, and Dynamic Overlay. These functions may be turned off to restore the mouse buttons to their normal operation. To see which function has control of the mouse, see Displaying Mouse Button Descriptions.

The Image Window Menu Bar

Use the Image window menu bar to select common interactive display functions. When a function is selected from one of the menus on this menu bar, the function applies only to the active display (see The Image Window Menu Bar).

Mouse Button Functions in the Image Window

Table 3-1: Functions of the Mouse Buttons in the Image Window

Table 3-1: Functions of the Mouse Buttons in the Image Window
Mouse Button	Function
Left Button	Click inside the Zoom box and drag it to a new location. The Zoom window updates when the button is released. Click to center the Zoom box over the current pixel position. Continue to hold the button and drag to continuously update the Zoom window. Double-click in the Image window to display the Cursor Location/Value dialog.
Middle Button	No function.
Right Button	Click to display the right-click menu.

The Zoom Window

The Zoom window is a small image display window that displays a portion of the image at a user-defined zoom factor. The Zoom window provides you with virtually unlimited zoom capabilities such as zooming in or out and panning.

Resizing the Zoom Window

Dynamically resize the Zoom window by grabbing one of the corners and dragging it to the desired image size. The corresponding Zoom box in the Image window automatically changes its size and shape to match the displayed Zoom window.

From the Image window menu bar, select File

Preferences and enter the size in the Display Preferences dialog (see Resizing Windows).

Change the default Zoom window size parameters set in the envi.cfg configuration file (see Customizing ENVI).

Scrolling the Zoom Window

Use the arrow keys on the keyboard to move the Zoom window by one pixel in the direction of the arrow.

Use Shift + arrow to move the Zoom window by five pixels in the direction of the arrow.

Displaying Zoom Window Scroll Bars

Use the scroll bars in the border of the Zoom window to move around the image. When you move the scroll bars, the graphic box in the Scroll window moves to show you what part of the whole image you are in. There are three ways to display the Zoom window scroll bars:

Displaying Scroll Bars at all Times

Select File

Preferences.

In the Edit System Preferences dialog, select the Display Defaults tab. The Preferences: Display Defaults dialog appears.

Click the Zoom Scroll Bars arrow toggle button to select Yes.

Click OK.

In the Edit System Preferences window, select File

Save Configuration.

Note
To exit without saving, select File

Cancel.

Enter an output filename and click OK.

Turning Display Scroll Bars On/Off

Right-click in the Zoom window and select Toggle

Display Scroll Bars or in the Zoom window, select File

Preferences. The Display Preferences dialog appears.

In the Zoom Window section of the dialog, click the Scroll Bars arrow toggle button to select Yes or No.

Click OK.

Controlling the Zoom Factor of the Zoom Window

The current zoom factor displays as a number in parentheses in the Zoom window title bar. The default zoom factor is 4.

Use the different mouse buttons and the Zoom controls in the Zoom window to change the zoom factor and to turn the display crosshairs on and off in both the Zoom and Image windows. The following table describes the Zoom window's symbol functions and associated mouse button descriptions.

Table 3-2: The Zoom Window Control Functions with Mouse Button Descriptions

Table 3-2: The Zoom Window Control Functions with Mouse Button Descriptions
Zoom Window Control	Function
Plus	Click with left mouse button to increase zoom factor by 1. Click with middle mouse button to double the zoom factor with each click (i.e., 2, 4, 8, 16). Click with right button to return to the default zoom factor of 4.
Minus	Click with left mouse button to decrease zoom factor by 1. Click with middle mouse button to decrease zoom factor by half. Click with right mouse button to return to the default zoom factor of 4.
Crosshair Box	Click with left mouse button to toggle crosshairs on and off in Zoom window. Click with middle mouse button to toggle crosshairs on and off in the Image window. Click with right mouse button to toggle the Zoom box and crosshairs in the Image window on and off.

Mouse Button Functions in the Zoom Window

In addition to the mouse button functions associated with the Zoom window Zoom controls and controlling the zoom factor, the left and right mouse buttons perform differently when clicked anywhere else inside the Zoom window (not on the Zoom controls). The following table describes those functions.

Table 3-3: Mouse Button Functions Inside the Zoom Window

Table 3-3: Mouse Button Functions Inside the Zoom Window
Mouse Button	Function
Left Button	Click on desired pixel to center the Zoom window on that pixel. or: Click and hold to pan from the center of the window in the direction of the cursor location. (The speed of the pan varies with the cursor's distance from the center of the Zoom window - the closer the cursor is to the center, the slower the pan.)
Middle Button	No function.
Right Button	Click to display the right-click menu.

Controlling Zoom Window Interpolation

You can set your preference for what kind of interpolation is used in the Zoom window. The default setting is pixel replication, also known as nearest neighbor. Set the interpolation by clicking the right mouse button in the Zoom window and making a selection from the Zoom Interpolation menu or set it through the System Preferences dialog as follows:

From the Image window menu bar, select File

Preferences.

From the Zoom Interp drop-down button, select the interpolation method: Nearest Neighbor, Bilinear, Bicubic, or Optimized Bicubic.

Note
Nearest neighbor uses pixel replication; bilinear does a linear interpolation using 4 pixels; bicubic uses 16 pixels for the interpolation; optimized bicubic provides the best interpolation.

Note
When you use the Cursor Location/Value window to view values in the Zoom window, the values you see reported are from the original data, not the interpolated data.

The Scroll Window

The Scroll window is a small image display window that appears when the display window style is set to Scroll/Zoom or Scroll/Image/Zoom and the main image is larger than can be displayed in the Image window at full resolution. The image in the Scroll window displays at subsampled resolution. The resampling factor appears in parenthesis in the title bar. The Image box appears as an outlined area within the Scroll window and delineates the area that displays in full resolution in the Image window.

Resizing the Scroll Window

Dynamically resize the Scroll window by grabbing a corner and dragging to the desired image size. The resampling factor changes to reflect the new size of the Scroll window.

From the Image window menu bar, select File

Preferences and enter the size in the Display Preferences dialog (see Resizing Windows).

Change the default Scroll window size using the parameters set in the envi.cfg configuration file (see Customizing ENVI).

Controlling the Image window from the Scroll Window

The size of the Image box in the Scroll window is directly linked to the size of the Image window. If you change the size of the Image window, the Image box also changes sizes. If you have the display window style set to Scroll/Image/Zoom and you resize the Image window so that the entire image appears at full resolution, the Scroll window closes as it is no longer needed. If you subsequently resize the Image window so that the full image cannot be shown at full resolution, the Scroll window reopens.

Use the arrow keys on the keyboard to move the Image window by one scroll pixel in the direction of the arrow. Use Shift + arrow to move the Image window in larger increments in the direction of the arrow.

Scroll Window Meta Zoom

When very large images display, the Scroll window image may be subsampled so much that it is difficult to see image features. The Scroll window Meta Zoom capability allows you to zoom into an area and reduce the subsampling factor in the Scroll window. The zoomed area replaces the full image in the Scroll window and scroll bars appear. The original Scroll window image can be re-displayed with a mouse click (see Mouse Button Functions in the Scroll Windowfor mouse button functions).

To zoom in the Scroll window, click and drag using the middle mouse button to draw the meta zoom indicator box around the desired area. This area replaces the image in the Scroll window.

To display the original full image in the Scroll window, right-click in the Scroll window and select Reset Scroll Range.

Mouse Button Functions in the Scroll Window

Table 3-4: Mouse Buttons Functions Inside the Scroll Window

Table 3-4: Mouse Buttons Functions Inside the Scroll Window
Mouse Button	Function
Left Button	Click anywhere outside the Image box in the Scroll window and drag. The Zoom and Image windows update continuously. Click, drag, and release the Image box to reposition the image. The Zoom and Image windows update when you release the mouse button. or: Click to center the Image box and image display over the selected pixel.
Middle Button	Click and drag meta zoom box.
Right Button	Click to display the right-click menu.

Image Window Right-Click Menu

Use the right-click menu in any of the three display windows to quickly access Image window options.

Right-click anywhere in any of the three display windows.

Select from the following options:

Use Display Window Style to select which of the three display windows (Image, Scroll, and Zoom) are shown.

Use Scroll/Zoom Position to place the Scroll and Zoom windows in the desired position with respect to the Image window and to turn the Auto Placement option off or on.

Use <Find Display> to locate the closed display windows associated with the current display window.

Positioning the Zoom and Scroll Windows

To position the Zoom and Scroll windows with respect to the Image window, select Scroll/Zoom Position from the right-click menu.

To position the Zoom or Scroll window, left-click and drag the title bar and drag the title bar.

To group the Zoom and Scroll windows to move with the Image window, deselect the Scroll/Zoom Position

Auto Placement Off option in the right-click menu. To ungroup the window, set Scroll/Zoom Position

Auto Placement Off in the right-click menu.

Locking Window Placement

To ensure that windows remain where they are placed, select Scroll/Zoom Position

Auto Placement Off.

Hiding Scroll/Zoom Windows

To hide only the Zoom and/or Scroll windows on Microsoft Windows platforms, click the

button in the right corner of the window.

Unhiding Scroll/Zoom Windows

Right-click in the Image, Zoom, or Scroll window and click <Find Display> to bring up the associated hidden Zoom and/or Scroll windows.