A Gimp Plugin that uses

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A Gimp Plugin that uses GrabCut to perform
image segmentation

• Project Proposal and Overview
• By Matthew Marsh

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What is Image Segmentation?

• Divides an image into parts
• Easy for humans
• Non Trivial for Computers

• 3 Types of Segmentation
• Thresholding
• Edge Based
• Region Based

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An Alpha Matte

• All Segmentation Techniques Create an alpha matte
• This is just a labeling of pixels
• Some methods allow an alpha value between 0 and 1

Alpha Matte Created After Segmentation
Origional Image
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Previous Approaches to Segmentation

• Magic Wand
• User specifies point
• Segmentation based on variable tolerance level of
  color statistics.

• Intelligent Scissors
• User Draws minimum cost contour
• Various seed points
• Not effective for highly textured areas e.g long
  strands of hair

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GrabCut

• Innovative uses region and edge information
• Also performs border matting
• Based upon graph cut

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Graph cut

• For greyscale images
• Cost function which depends on Edge and Region
  Information
• Minimize cost function to obtain best cut
• Cost function in minimized by a Max Flow Algorithm

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How Graph Cut Works

• To perform segmentation the user provides seeds
• Pixels labeled as definitely background or
  foreground (Hard constraints)
• Cost function defined by boundary and rejoin
  properties (Soft constraints)
• Cutting along the path of least cost produces
  best segmentation

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Graph cut
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How GrabCut extends graph cut

• Uses GMMs to work with colour images
• Alows an iterative approach to segmentation
• Adds Border Matting

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GrabCuts Interactive Approach to Segmentation
Initial Selection
Refinement
Final Segmentation
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My Project

• A Gimp Plugin Using GrabCut
• Initial Simplifications
• Use Graph cut approach
• No Max flow algorithm
• Later Add
• Max flow algorithm
• Color functionality using GMMS
• Border matting