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I am playing with a weird dataset of ternary images (+1,0,-1 values only) which happen to be very sparse (avg. > 90%). I would like to determine the most relevant "islands" (or should I call them blobs) of non-zero elements.

Algorithm complexity is a key factor since I would like (hopefully) to deploy it in real-time over frames acquired by an RGB camera.

Any suggestion/pointer would help.

Thanks!

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    $\begingroup$ How do you define "relevant"? You might look for large connected components (say for nearest-neighbours, or nearest and next-nearest). $\endgroup$ Commented Mar 6, 2019 at 18:44
  • $\begingroup$ With "relevant" I meant the first N islands as sorted by size (i.e. number of non-zero elements). At the moment I am working on a simple algorithm that recursively partitions the focal plane and counts the non-zero elements combined with some heuristics (thresholds) I extrapolated from the dataset. However it is not general and might not be performant enough. Thanks for your inputs, i will post the solution if I find (an efficient) one. $\endgroup$ Commented Mar 7, 2019 at 9:14
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    $\begingroup$ The standard algorithms for finding connected components in a graph use either breadth-first search or depth-first search, and are $O(V+E)$ for a graph with $V$ vertices and $E$ edges. $\endgroup$ Commented Mar 7, 2019 at 12:35

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