Region Adjacency Graph (RAG)

Computes the graph of adjacent regions in a labeled image

Description

Computes region adjacency graph of a labeled 2D or 3D image.

Two regions are considered as neighbor if they are separated by a background (i. e. with color 0) pixel in the horizontal or vertical direction, as well as depth direction for 3D images.

The result is a N*2 array, containing 2 indices for each couple of neighbor regions.

usage:
ADJ = imRAG(IMG);
ADJ has the format [LBL1 LBL2], LBL1 and LBL2 being vertical arrays the same size.
 
LBL1 is given in ascending order, LBL2 is given in ascending order for each LBL1. Ex :
    [1 2]
    [1 3]
    [1 4]
    [2 3]
    [2 5]
    [3 4]
 
Alternative syntax:
[NODES, ADJ] = imRAG(IMG);
Return two arrays: the first one is a [N*2] array containing centroids of the N labeled region, and ADJ is the adjacency previously described.

For 3D images, the node array is [N*3].

• MATLAB release: MATLAB 7.5 (R2007b)
• Other requirements: image processing toolbox is not required to run the function, but is required to run the example code.

[Perrine Paul]

Very efficient. Some example of use would be of interest, for accessing data.

[Joao Henriques]

 

[Ryan]

Very useful.