The Zoomify Image Viewer can display two Zoomify Images side-by-side for synchronized comparison viewing! One simple HTML parameter, zComparisonPath, is used to provide the path to a simple XML (text) file that includes the image paths for the two Zoomify Images, as well as any image-specific values such as initial view coordinates.

Two Navigators are also displayed (the pair are optional), and a 'Sync' checkbox is added to the Toolbar to permit unsynchronized viewing. When unsync'd, each Navigator affects its own Viewport, and the Toolbar and shortcut keys affect the 'active' Viewport - the Viewport with the Navigator displaying a selection border. Switch between Viewports using the Page Up and Page Down keys or by clicking in a Viewport or Navigator. Two optional parameters provide additional control: zSyncVisible and zIntialSync. Complete information is provided in the Parameter List.htm document in the documentation folder.

Note that comparison viewing is typically used with two images with matching dimensions. Side-by-side comparison of images of different sizes or aspect ratios is possible but the synchronized viewing is less useful when, for example, panning to the far edge of one image might mean panning beyond the edge of the comparison image (in which case default pan constraint functionality will simply limit the motion of the second image).