GRASS GSoC 2012 Image Segmentation

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(See also other GRASS GSoC 2012 projects)

Student Name: User:Emomsen
Organization: OSGeo - Open Source Geospatial Foundation
Mentor Name: Mentor: Markus Metz (backup mentors: M Lennert, P Roudier)
Title: Image Segmentation

Abstract

GRASS GIS has many imagery related processing capabilities, but the field is rapidly developing and many techniques are not yet implemented. The goal of this GSoC project is to implement the region growing image segmentation algorithm.

Input: Raster map(s) to be segmented (plus optional vector map for a constraint)

Output: To include segmented regions with statistics. This information can be directly used or taken as input to existing image classification modules.

Background

Image classification techniques already implemented in GRASS GIS include supervised and unsupervised classification. Classification of images based on pixels can often be very noisy. By first segmenting the image, later classification of 'objects' can be more effective. Noise is reduced, classification speed is increased, and most importantly the classification is performed on objects instead of pixels. The i.smap module does include a segmentation step (based on Gaussian mixture distribution), but there does not exist a module intended to segment the image and provide segment data for general use. A summary of the existing methods implemented in GRASS are at Image classification. Furthermore, the module r.seg in GRASS-addons uses internally the Mumford-Shah variational model for image segmentation.

Main Goal

Implement an image segmentation method to extend the available options for image processing in GRASS. The region growing method has been selected as a robust general purpose method. An important contribution of the new method will be to include vector maps (for example road networks) as a constraint in growing the segments. Output from the module will include Spectral (mean/variance/range/ect) and Spatial (area/shape/location/etc) data for each region.

Specifications

  • Input
    • any raster map, but generally satellite or areal images that are pre-processed and ready for analysis (i.e. no pre-processing in the module)
    • optionally vector maps of existing features
      • linear feature would indicate compulsory limits of segments
      • polygonal features would indicate existing known segments
  • Algorithm of segmentation
    • in GSoC implementation of only one algorithm
    • code should be structured to allow easy implementation of additional algorithms
    • multi-scalar segmentation can significantly improve results and should thus be implemented if possible (see i.smap code for example)
  • Output
    • raster map of segments (i.e. each pixel value represents id of segment the pixel belongs to)
    • vector map of segments with a series of attributes
      • spectral attributes: XXX
      • textural attributes: XXX
      • morphological attributes: XXX
    • depending on segmentation algorithm: raster map indicating for each pixel the probability of belonging to the segment it was put into, i.e. some measure of reliability of results

Project Plan

Preparation: Gather ideas from the community! Feature requests, image segmentation literature, and any other ideas and suggestions.

  • May 21: Start coding, 8 weeks until Midterm Evaluation
  • Week 1: Develop pseudocode to outline the work
  • Week 2-4: Implement the main algorithm
  • Week 5: Add vector maps as a constraint to the segmentation
  • Week 6: Validation
  • Week 7: Debugging
  • Week 8: GUI
  • July 9: Midterm Evaluation: Evaluate the existing program, determine the plan for the remaining 3-4 weeks. Options include:
  • Improving the main algorithm
  • Adding control for what scale the segmentation is performed at
  • Providing updates to i.maxlik to ensure the segmentation output can be used as input for the existing classification functionality