Computation times for 20 iterations:

The optimized version is approximately 217 times faster than the "old version" and 24 times faster than the "new version" implemented by sakri.

ES2015 features like TypedArrays, const and local scoping are used to gain this speed up.

Test it yourself with this online benchmark / demo.

Marching squares outlines blobs of non-transparent pixels inside a bitmap.

This is a straight forward port from this excellent implementation by Phill Spiess:

http:https://devblog.phillipspiess.com/2010/02/23/better-know-an-algorithm-1-marching-squares/

This is a Javascript implementation designed to be used with Html5 Canvas.

Check out the code in marchingSquaresTest.html for usage example.

http:https://htmlpreview.github.io/?https://github.com/sakri/MarchingSquaresJS/blob/master/marchingSquaresTest.html

Here's a few codepen demos using it:

A visualization of the algo as it executes http:https://codepen.io/sakri/full/aIirl

Text Edge Flare http:https://codepen.io/sakri/full/vIKJp

Ghost text http:https://codepen.io/sakri/full/zbqti

He-Man effect http:https://codepen.io/sakri/full/wsiLC

Here's a demo that tackles "blobs with holes" as in getting the outline for characters such as "O" "8" "&" etc. http:https://codepen.io/sakri/pen/LCrDe

If there is interest, I can include the required code in this repo (floodFill, basic threshold etc.)

Have a good day!