SAOimage display of M-51

Panning and Zooming in SAOimage

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The loaded image may be panned and/or zoomed for its display in the central display window. Panning and zooming are interactively controlled by clicking or dragging the mouse in the pan window. This is the small image window at the top of the desktop, next to the magnifier.

The pan window shows the entire area of the loaded image. (By default the image in the pan window was reduced by taking the maximum value in each block of the original image, but averaging, summing, or subsampling may be used instead - see the cmdline section). A box cursor in the pan window shows the area of the image currently being displayed in the main display window. This box can be moved and sized just like the regular box cursor (but without angular rotation control).

The left mouse button controls the location of the center of the box (the display image). The middle button controls the edge of the box, for the given center, thus determining its size. The size of the box is restricted to integer zoom factor. (The actual algorithm choses the smallest zoom that still includes the mouse pointer's position.) One can switch from one type of control to the other, by holding the first button down, until after the second button has been pressed. The interaction can be cancelled by dragging the pointer outside of the pan window's borders. Only after the last button is released is the main display redrawn, with the indicated pan and zoom.

When the mouse is in the pan window, the area under the mouse pointer can be magnified in the magnifier by pressing or holding the shift key on the keyboard. The "T" key table also works with the pointer in the pan window (see the keyboard section). As anywhere else, the arrow keys can be used for fine positioning.

In pan mode, the same types of interactions as those used in the pan window can be performed in the main display window. Clicking or dragging with the left button controls the center of the display. Clicking or dragging with the middle button determines the zoom factor. The box cursor in the pan window tracks these manipulations as the mouse is dragged in the display window, just as it does when it is being directly manipulated in the pan window.

The "pan" submenu allows a more basic method of changing the zoom (e.g. x4 or x1/2). The center button centers the display on the image and the zoom 1 sets it to one display pixel per image pixel.