MATLAB: Greetings. I want to ask on how to find the centre of the this black line by using image processing tool? currently i am doing the project and i stuck to find the centroid of the line.

image processingImage Processing Toolboxline follower

How about you just get the skeleton?

skelImage = bwmorph(~binaryImage, 'skel', inf);

Maybe one of these links will give you some ideas about how to get started:

In short

binaryImage = yourImage < 128;
props = regionprops(binaryImage, 'Area', 'Perimeter');
allAreas = [props.Area]
allPerimeters = [props.Perimeter];

You can add other parameters is you wish.