Blob extraction

Blob extraction is an image segmentation technique that categorizes the pixels in an image as belonging to one of many discrete regions. Blob extraction is generally performed on the resulting binary image from a thresholding step. Blobs may be counted, filtered, and tracked.

Inconsistent terminology for this procedure exists, including region labeling, connected-component labeling, blob discovery, or region extraction.

Well-known algorithms for accomplishing this exist, including a sequential algorithm and recursive algorithm.

Blob extraction appears to be related to but distinct from "blob detection".

equential algorithm

Create a region counter

Scan the image (in the following example, it is assumed that scanning is done from left to right and from top to bottom):

* For every pixel check the "north" and "west" pixel (when considering 4-connectivity) or the "northeast", "north", "northwest", and "west" pixel for 8-connectivity for a given region criterion (i.e. intensity value of 1 in binary image, or similar intensity to connected pixels in gray-scale image).

* If none of the neighbors fit the criterion then assign to region value of the region counter. Increment region counter.

* If only one neighbor fits the criterion assign pixel to that region.

* If multiple neighbors match and are all members of the same region, assign pixel to their region.

* If multiple neighbors match and are members of different regions, assign pixel to one of the regions (it doesn't matter which one). Indicate that all of these regions are the equivalent.

Scan image again, assigning all equivalent regions the same region value.

References

cite book
last = Horn
first = Berthold Klaus Paul
title = Robot Vision
publisher = MIT Press
date = 1986
pages = 69-71
id = ISBN 0-262-08159-8

ee also

*Connected component (graph theory)
*Blob detection
*Connected component labeling
*flood fill

External links

* [http://opencvlibrary.sourceforge.net/cvBlobsLib OpenCV Blob Extraction Library]