title: How can I find the boundary surface in this image
body: <p>I am new to image processing. I want to find the surface between black and white pixels which separates them. Here is the link of image. 
  The size of image is (21,900,900) </p>
  
  <p><a href="https://drive.google.com/file/d/1zUWK0Fb_n6f1JZou5mrUJq0x3h2X8mBK/view?usp=sharing" rel="nofollow noreferrer">https://drive.google.com/file/d/1zUWK0Fb_n6f1JZou5mrUJq0x3h2X8mBK/view?usp=sharing</a></p>
  
  <p>I tried to use boundarymask command of MATLAB in one plane of image but I am getting noise and also it works for 2d image only. Please suggest me how to find boundary 3d surface  here. Thank you. 
  This is the output image after applying boundarymask. </p>
  
  <p><a href="https://i.stack.imgur.com/02kRD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/02kRD.png" alt="How to find surface boundary between white and black"></a> </p>