To rotate an image by an angle multiple of 90 degrees:
Activate the window in which the target image is located. To do this, click the left mouse button on the window area or header (marked by the arrow in Fig. 5.13).
Click on the arrow on the right side of the Rotate by 90 degrees clockwise button and select the angle from the drop-down menu.
To restore the initial image position, select the Set 0 degrees rotation angle item.
To rotate the image by 90 degrees clockwise, just click on the left side of the Rotate by 90 degrees clockwise button.
To cancel the rotation of all the images, click the Reset view orientation button on the toolbar . Note that all the other view conversions will be undone as well.
This tool is also available from the image context menu and from the MPR main menu item.