Connected Component Labeling (CCL) is an important step in pattern
recognition and image processing. It assigns labels to the pixels such that
adjacent pixels sharing the same features are assigned the same label.
Typically, CCL requires several passes over the data. We focus on two-pass
technique where each pixel is given a provisional label in the first pass
whereas an actual label is assigned in the second pass.
We present a scalable parallel two-pass CCL algorithm, called PAREMSP, which
employs a scan strategy and the best union-find technique called REMSP, which
uses REM's algorithm for storing label equivalence information of pixels in a
2-D image. In the first pass, we divide the image among threads and each thread
runs the scan phase along with REMSP simultaneously. In the second phase, we
assign the final labels to the pixels. As REMSP is easily parallelizable, we
use the parallel version of REMSP for merging the pixels on the boundary. Our
experiments show the scalability of PAREMSP achieving speedups up to $20.1$
using $24$ cores on shared memory architecture using OpenMP for an image of
size $465.20$ MB. We find that our proposed parallel algorithm achieves linear
scaling for a large resolution fixed problem size as the number of processing
elements are increased. Additionally, the parallel algorithm does not make use
of any hardware specific routines, and thus is highly portable.Comment: Parallel & Distributed Processing Symposium Workshops (IPDPSW), 201