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Understanding Boundary Fill and Flood Fill Algorithms in Graphical Applications

This resource explores the boundary fill and flood fill algorithms used in graphical applications, with a focus on pixel-based methods. The boundary fill starts at an interior point and fills outwards until it encounters a boundary pixel color. In contrast, flood fill replaces a consistent color throughout a designated area. The tutorial also discusses variations like 4-connected and 8-connected fill, recursive algorithms, and potential issues such as stack space problems. This guide is beneficial for students and professionals interested in computer graphics and image processing.

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Understanding Boundary Fill and Flood Fill Algorithms in Graphical Applications

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  1. Filling Graphical ShapesPixel-based methods

  2. Boundary Fill • MS Paint CS-321Dr. Mark L. Hornick

  3. Boundary Fill • Start at interior point • “Paint” interior outward toward boundary • How? • Note: Boundary encounter determined by boundary pixel color CS-321Dr. Mark L. Hornick

  4. Boundary fill Interior point CS-321Dr. Mark L. Hornick

  5. Boundary Fill Algorithm • Don’t fill if current position is: • Boundary color • Current fill color • Otherwise • Set fill color • Recursively try neighbors • North, East, South, West • Could also be NSEW, NEWS, etc. • Each neighbor recursively performs algorithm until “stop” CS-321Dr. Mark L. Hornick

  6. Boundary Fill Patterns 4-connected 8-connected CS-321Dr. Mark L. Hornick

  7. 4-connected EWNS boundary fill CS-321Dr. Mark L. Hornick

  8. Boundary Fill Algorithm • Demo CS-321Dr. Mark L. Hornick

  9. Boundary Fill Problems • Recursive algorithm • Stack space issue • Recursion stops only on • Boundary color • Current fill color • What if some other fill color is already present? • i.e. pixels already in area to be filled CS-321Dr. Mark L. Hornick

  10. Flood Fill • Similar to boundary fill • But replaces “interior” color (i.e. not boundary) • Floods through an area • Fill area must be - initially – a consistent color • Only one significant color is filled over • Paint bucket tool • MS Paint actually uses flood fill CS-321Dr. Mark L. Hornick

  11. Fill Algorithm Summary • Vector edge model • Scan line fill • Even-odd or non-zero winding • Pixel model • 4- or 8- connected recursion • Boundary fill: overwrites all but boundary or current fill color • Flood fill: overwrites only initially selected color CS-321Dr. Mark L. Hornick

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