How to get the coordinates of pixels present in a block after doing quad tree decomposition

Hey guys, Actually, I am doing a project and for this I am doing the quad tree decomposition of an image but after that I need to get the coordinates of the pixels present a block so that I can do something with them.

Can anyone can suggest me something or give me some code by using which I will be able to extract the coordinates of the pixels or I get to know which pixels are there in a block.

Thanks please reply!