The Q/A button brings up the Q/A Panel. The Q/A panel can be used to reverse the results of the currently active effect. The Q/A panel works similarly to the Paint effect. Select the region of the frame you want to undo by drawing either a rectangle or ellipse, by lassoing the area or by painting the area with the undo brush.
The Rectangle, Ellipse, Lasso and Brush buttons specify how undo areas are selected in the Cinema. In brush mode, the size of the brush can be changed by shift-dragging the mouse in the Cinema.
For some effects like Auto Dirt Fix that have individual fix areas, the fixes can be reviewed by clicking the View button. For those effects the Area button will be enabled. With the Area button pressed, a fix can be undone by simply left clicking it in the Cinema.
Undo areas are listed in the undo list. The name and in and out frame of an undo stroke can be changed by directly editing the values in the undo list.
By default, each undo area will initially exist only in the frame in which it is drawn. Clicking the Make Multi button will update the in/out points of all selected areas to cover the entire clip. The in/out points can also be edited by double-clicking in the relevant column, or by using the buttons underneath the list. Clicking the Make Single button willl reduce the in/out points of all selected areas to cover the current frame only.