Routines (alphabetical) > Routines: Z > ZOOM Procedure

# ZOOM Procedure

The ZOOM procedure displays part of an image from the current window enlarged in a new (“zoom”) window. The cursor is used to mark the center of the zoom area, and different zoom factors can be specified interactively.

Note: ZOOM only works with color systems.

This routine is written in the IDL language. Its source code can be found in the file `zoom.pro` in the `lib` subdirectory of the IDL distribution.

### Using ZOOM

After calling ZOOM, place the mouse cursor over an image in an IDL graphics window. Click the left mouse button to display a magnified version of the image in a new window. The zoomed image is centered around the pixel selected in the original window. Click the middle mouse button to display a menu of zoom factors. Click the right mouse button to exit the procedure.

### Using ZOOM with Draw Widgets

Note that the ZOOM procedure is only for use with IDL graphics windows. It should not be used with draw widgets. To obtain a zooming effect in a draw widget, use the CW_ZOOM function.

## Syntax

ZOOM [, /CONTINUOUS] [, FACT=integer] [, /INTERP] [, /KEEP] [, /NEW_WINDOW] [, XSIZE=value] [, YSIZE=value] [, ZOOM_WINDOW=variable]

## Arguments

None

## Keywords

### CONTINUOUS

Set this keyword to make the zoom window track the mouse without requiring the user to press the left mouse button. This feature only works well on fast computers.

### FACT

Use this keyword to specify the zoom factor, which must be an integer. The default zoom factor is 4.

### INTERP

Set this keyword to use bilinear interpolation. The default is to use pixel replication.

### KEEP

Set this keyword to keep the zoom window after exiting the procedure.

### NEW_WINDOW

Normally, if ZOOM is called with KEEP and then called again, it will use the same window to display the new zoomed image. Set the NEW_WINDOW keyword to force ZOOM to create a new window for this purpose.

### XSIZE

Use this keyword to specify the X size of the zoom window. The default is 512.

### YSIZE

Use this keyword to specify the Y size of the zoom window. The default is 512.

### ZOOM_WINDOW

Set this keyword to a named variable that will contain the index of the zoom window. KEEP must also be set. If KEEP is not set, ZOOM_WINDOW will contain the integer -1.

## Examples

### Zooming in on a Direct Graphics Image Display

The following example imports a grayscale image from the `convec.dat` binary file. This grayscale image shows the convection of the Earth’s mantle. The image contains byte data values and is 248 pixels by 248 pixels. The ZOOM procedure, which is a Direct Graphics routine, is used to zoom in on the lower left corner of the image.

See `zooming_direct.pro` in the `examples/doc/image` subdirectory of the IDL installation directory for code that duplicates this example. Run the example procedure by entering `zooming_direct` at the IDL command prompt or view the file in an IDL Editor window by entering `.EDIT zooming_direct.pro`.

1. Determine the path to the `convec.dat` file:

   file = FILEPATH('convec.dat', $

   SUBDIRECTORY = ['examples', 'data'])

2. Initialize the image size parameter:

   imageSize = [248, 248]

3. Import the image from the file:

   image = READ_BINARY(file, DATA_DIMS = imageSize)

4. If you are running IDL on a TrueColor display, set the DECOMPOSED keyword to the DEVICE command to zero before your first color table related routine is used within an IDL session or program.

   DEVICE, DECOMPOSED = 0

5. Load a grayscale color table:

   LOADCT, 0

6. Create a window and display the original image with the TV procedure:

   WINDOW, 1, XSIZE = imageSize[0], YSIZE = imageSize[1], $

   TITLE = 'A Grayscale Image'

   TV, image

   The following figure shows the resulting grayscale image display.

7. Use the ZOOM to enlarge the lower left quarter of the image:

   ZOOM, /NEW_WINDOW, FACT = 2, $

   XSIZE = imageSize[0], YSIZE = imageSize[1]

   Click in the lower left corner of the original image window.

   The following figure shows the resulting zoomed image.

8. Right-click in the original image window to quit out of the ZOOM procedure.

## Version History

Original | Introduced

## See Also

CW_ZOOM, ZOOM_24 Procedure