What is the purpose of 'Onion Skinning' in Storyboard Pro?

Onion Skinning serves an essential function in Storyboard Pro by allowing the artist to view previous and subsequent frames simultaneously. This technique is crucial for maintaining continuity throughout a project, as it enables the storyboard artist to ensure that movements and actions flow smoothly from one frame to the next. By visualizing multiple frames at once, artists can make informed decisions about timing, transitions, and the consistency of character and scene design. This capability is particularly beneficial when refining animations or ensuring that visual storytelling aligns perfectly across different stages of the storyboard. The other options do not pertain to the fundamental utility of Onion Skinning, which specifically focuses on the previewing of frames rather than sound effects, color palettes, or text annotations.