An ILP Solver for Multi-label MRFs with Connectivity Constraints
This provides a tool for generating ground-truth labels and proposals in image segmentation, particularly useful for offline quality checks and weakly supervised learning, though it is incremental as it builds on prior LP relaxations.
The paper tackles the problem of solving multi-label Markov random fields with exact connectivity constraints using an integer linear programming approach, achieving globally optimal solutions via a branch-and-cut method and demonstrating effectiveness on datasets like BSDS500 and PASCAL.
Integer Linear Programming (ILP) formulations of Markov random fields (MRFs) models with global connectivity priors were investigated previously in computer vision, e.g., \cite{globalinter,globalconn}. In these works, only Linear Programing (LP) relaxations \cite{globalinter,globalconn} or simplified versions \cite{graphcutbase} of the problem were solved. This paper investigates the ILP of multi-label MRF with exact connectivity priors via a branch-and-cut method, which provably finds globally optimal solutions. The method enforces connectivity priors iteratively by a cutting plane method, and provides feasible solutions with a guarantee on sub-optimality even if we terminate it earlier. The proposed ILP can be applied as a post-processing method on top of any existing multi-label segmentation approach. As it provides globally optimal solution, it can be used off-line to generate ground-truth labeling, which serves as quality check for any fast on-line algorithm. Furthermore, it can be used to generate ground-truth proposals for weakly supervised segmentation. We demonstrate the power and usefulness of our model by several experiments on the BSDS500 and PASCAL image dataset, as well as on medical images with trained probability maps.