Zoom plugin

The Zoom plugin shows an enlarged image of a cutout region centered under the cursor position in the associated channel image. As the cursor is moved around the image, the zoom image updates to allow close inspection of the pixels or precise control in conjunction with other plugin operations.

Plugin Type: Global

Zoom is a global plugin. Only one instance can be opened.


The magnification of the zoom window can be changed by adjusting the “Zoom Amount” slider.

Two modes of operation are possible – absolute and relative zoom:

  • In absolute mode, the zoom amount controls exactly the zoom level shown in the cutout; For example, the channel image may be zoomed into 10X, but the zoom image will only show a 3X image if the zoom amount is set to 3X.

  • In relative mode, the zoom amount setting is interpreted as relative to the zoom setting of the channel image. If the zoom amount is set to 3X and the channel image is zoomed to 10X then the zoom image shown will be 13X (10X + 3X). Note that the zoom amount setting can be < 1, so a setting of 1/3X with a 3X zoom in the channel image will produce a 1X zoom image.

The “Refresh Interval” setting controls how quickly the Zoom plugin responds to the movement of the cursor in updating the zoom image. The value is specified in milliseconds.


Usually setting a small refresh interval improves the overall responsiveness of the zoom image, and the default value of 20 is a reasonable one. You can experiment with the value if the zoom image seems too jerky or out of sync with the mouse movement in the channel image window.

The “Defaults” button restores the default settings of the controls.

It is customizable using ~/.ginga/plugin_Zoom.cfg, where ~ is your HOME directory:

# Zoom plugin preferences file
# Place this in file under ~/.ginga with the name "plugin_Zoom.cfg"

# default zoom level
zoom_amount = 3

# refresh interval (sec)
# NOTE: usually a small delay speeds things up
refresh_interval = 0.02