Image Pane - Main Window
The image pane is the region of the main window that displays the selected image. The image pane allows adjustment of display size and orientation; it also provides several methods to manipulate the image with the mouse and keyboard.
The image is drawn to the screen as it is decoded from disk. The image can be panned and zoomed while it is still loading. Image adjustment operations for rotation, mirror, and flip will delay until the image is completed. The adjustment queue will remember one operation and will retain the most recently requested function, which will be performed once the image has finished loading.
The quality of the image, especially when using the zoom feature, is dependent on the settings that are available on the Image tab of the preferences dialog.
To increase the speed of loading the next image when navigating the image list in sequence, enable the Preload next image option.
Image panning and manipulation
When the image size is larger than the image pane, the visible region can be changed with the keyboard or mouse. The keyboard can also be used to adjust the orientation of the image.
Keyboard: Use the arrow keys to pan the image in the desired direction, to increase the panning speed hold down the Shift key while pressing an arrow key. Press Control and an arrow key to move to the respective edge of the image. The image can only be panned with the keyboard when the image has the focus, indicated by a dotted line surrounding the image pane.
To scale the image size, use the [+] or [=] key to zoom in and the [-] key to zoom out. The [X] or keypad [*] key will scale the image to fit the available display area, the [Z] or keypad [/] key will reset the zoom to original image size. There are also keys to select a preset zoom factor:  = 1:1,  = 2:1,  =3:1,  = 4:1,  = 1:4,  = 1:3, and  = 1:2.
To rotate the image clockwise 90 degrees press the “]” key, to rotate counterclockwise 90 degrees press the “[“ key. To rotate the image 180 degrees use [Shift] + [R], the image can also be flipped horizontally or vertically with the respective [Shift] + [M] (mirror) and [Shift] + [F] (flip) keys.
Note: The rotation, mirror, and flip functions will not change the image file on disk.
Mouse: Press the primary mouse button on the image and hold it, then move the mouse to pan the image in the desired direction. Releasing the mouse button will stop the panning operation. The mouse wheel can also be used to scroll the image when holding down the [Shift] key (*).
To scale the image size hold down the [Control] key and scroll the mouse wheel up to zoom in, or down to zoom out.
Smooth Scroll: To start the smooth scroll function hold down the [Shift] key and click the primary mouse button. An icon will appear at the location of the mouse pointer, the mouse can then be positioned to pan the image. The image will pan in the direction of the mouse pointer relative to the icon. The pan speed will increase in proportion to the distance that the pointer is from the center of the icon. To end the smooth scroll function click the primary mouse button within the image pane.
The displayed image can be changed to the next or previous image using the keyboard or mouse.
Keyboard: The Page Down and Page Up keys will change the image to the next or previous image, respectively, in the list. The Home and End keys will jump to the first and last image, respectively. When the image has the focus, the Space and Back Space keys can also be used to change the image.
Mouse: To change to the next image in the list click the left mouse button, click the middle mouse button to change to the previous image. The mouse wheel can also be used to change the current image (*).
Right clicking the mouse or pressing the menu key while the image has the focus will display a menu. The menu functions will perform the same as those that match the window's menu bar, however a few functions are unique to the context menu:
View in new window: Opens a new window containing a second copy of the current image.
Pause slide show, Continue slide show: Controls the pause state of an active slide show, the text of the menu will change to reflect the action that will be performed.
Drag and Drop
Files and folders can be dropped onto the image pane, dropping a file will display the file and dropping a folder will change the main window to display the contents of the folder. When dropping multiple items on the image pane, only the first item in the list will be used, all additional items will be ignored.
A drag and drop operation can be initiated from the image pane with the middle mouse button, the dragged item will contain the file path of the displayed image.
(*) Note: The mouse wheel behavior for scrolling and image step can be swapped with the Mouse wheel scrolls image option located on the Advanced tab of the preferences dialog.
GQview User Manual