CSE 633 2010 Fall
Parallel Connected Component Labeling
For Image Analysis
Yang Fei
Dec. 7. 2010
Computer Science and Engineering
SUNY at Buffalo
Connected Component Labeling
Application
Widely used to group connected Pixels in Image
Distinguish segments of an image
Application: Medical Testing and Meteorological Image
Problem belong to subset of Connected Components
in Graph
Several Parallel problem about this topics
Image Analysis Example
Problem Description
• Using Binary image as example
pixels have two value 1 (object pixels)
0(background pixels)
• Labeling object
pixels with value equal to 1
Under 4-connectivity, adjacent pixels mark
as the same label
Two Pass algorithm
• First Pass
Scan each element of data by row
Assign temporary label to each element
Store equivalence between adjacent pixel
• Second Pass
Based on the equivalence table, scan image
again
Relabel the element with the lowest equivalent
label
Parallel
• Why parallel
time-consuming, need maintain large table for equivalent
label
• Parallel Method
Divide pixels into n parts
Assign each part to different processors
Try to decrease computation time of this algorithm
• Advantages
Each scan only on small size
Don t need maintain large equivalent table
Experiment
• Edge machine
• Used functions
MPI_Scatter MPI_Gather
• Input Image
Simulate binary image as two-dimensional
matrix (two-dimensional array)
Implementation
• Generate two-dimensional matrix on
root processor
• Assign each part to other processor by
MPI_Scatter
• Run two- pass algorithm on each processor
• Collect label information from each processor
• Relabel adjacent pixels on boundary and
relative pixels
Result
30
8 processors
25
4 processors
Time(ms)
20
15
10
5
0
64
256
576
1024
1600
2304
Number of Pixels
3136
4096
5184
6400
Result
40
35
30
time(ms)
25
20
pixels=6400
15
10
5
0
4
5
6
7
8
9
10
number of processors
12
14
16
Reference
Susanne Hambrusch
A Study of Connected Component Labeling Algorithm on The MMP
D. S. Hirschberg
A Parallel Graph Algorithm For Finding Connected Components
Jung-Me Park, Carl G.Looney
Fast Connected Component Labeling Algorithm Using A Divide and
Conquer Algorithm