When a project, album, or folder is selected in the Library inspector, Aperture offers three basic layouts for the main window:
Browser: Use this layout to display image thumbnails in an enlarged Browser so you can review photos, perform initial rating passes, and create and work with stacks of photos.
Split View: Use this layout to display both the Browser and Viewer together and use them in combination to review and work with photos.
Viewer: Use this layout to display photos in an enlarged Viewer and work with them in detail.
You can switch between layouts by pressing V, choosing commands from the View menu, or clicking buttons in the toolbar.
Do one of the following:
Choose Browser, Split View, Viewer, or Cycle View Mode from the View menu (or press V).
Click the Browser, Split View, or Viewer button in the toolbar.
In the Split View layout, the Browser appears horizontally under the Viewer by default. However, you can change the layout to display the Browser vertically, beside the Viewer.
Choose View > Browser > Rotate Position (or press Shift-W).
Choose View > Browser > Swap Position (or press Option-W).
Choose Aperture > Preferences, or press Command-Comma (,).
In the Preferences window, click Appearance, then drag the Viewer Brightness slider to lighten or darken the background.