Blob extraction

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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".

1 Sequential algorithm
2 References
3 See also
4 External links

[edit] Sequential algorithm

Create a region counter

Scan the image. 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 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.