Connected components, in a 2D image, are clusters of pixels with the same value, which are connected to each other through either 4-pixel, or 8-pixel connectivity. 4-pixel connectivity would group all pixels that contact each other on either of their four faces, while 8-pixel would group pixels that are connected along any face or corner. In 3D, your connectivity options, at least for rectangular pixels, are 6, 18, and 26 (faces, faces+edges, faces+edges+corners).

If it's at a all applicable, I'd like to to take moment recommend you take a look at our newly released image processing software at http://MIPAR.us. We offer several user-friendly ways to segment, and then rapidly calculate and display the connected components of 2D and 3D segmentations. Thanks for the question! 

Connected components, in a 2D image, are clusters of pixels with the same value, which are connected to each other through either 4-pixel, or 8-pixel connectivity. 4-pixel connectivity would group all pixels that contact each other on either of their four faces, while 8-pixel would group pixels that are connected along any face or corner. In 3D, your connectivity options, at least for rectangular pixels, are 6, 18, and 26 (faces, faces+edges, faces+edges+corners).

If it's at a all applicable, I'd like to to take moment recommend you take a look at our newly released image processing software at http://MIPAR.us. We offer several user-friendly ways to segment, and then rapidly calculate and display the connected components of 2D and 3D segmentations. Thanks for the question! 

Thank you for the Answer. Can I get information, Why we are using a connected Component in Text detection and by what is the working principle?

added on what is meant by Connected Component Analysis in text recognition

In text detection, connected component plays a vital role. Each connected component ensures that the underlying pixels forms a single character.  This helps in identification of characters.

hi 

for more detailed description check the paper

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6471224&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F83%2F6490370%2F06471224.pdf%3Farnumber%3D6471224

https://cvit.iiit.ac.in/papers/kaushik01cca.pdf

http://www.comp.nus.edu.sg/~cs4243/projects/TextDetectionSurvey.pdf

I have a practical sample for this analysis.You can refer to the following publication: 

Article Automatic building extraction in dense urban areas through G...

This paper discusses some of the important algorithms:

"What is the world's fastest connected component labeling algorithm? "

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6986069&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F6973465%2F6986048%2F06986069.pdf%3Farnumber%3D6986069

Your answer is in below link:

https://www.mathworks.com/help/images/ref/bwconncomp.html