title: Find pixel coordinates of grid intersection points
body: <p>I am trying to find a repeatable process to find the coordinates of grid intersection points from an image. The image is a montage of many smaller images. Each 'tile' of the montage has inconsistent contrast, so my naive methods are failing (the tile boundary is being selected) . A small example:</p>
  
  <p><a href="https://i.stack.imgur.com/ZNud9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZNud9.png" alt="Montaged grid"></a></p>
  
  <p>I have had minor advances from the ideas explained in <a href="https://stackoverflow.com/questions/10196198/how-to-remove-convexity-defects-in-a-sudoku-square">How to remove convexity defects in a Sudoku square?</a> and <a href="https://stackoverflow.com/questions/16476367/grid-detection-in-matlab">Grid detection in matlab</a></p>
  
  <p>However, the grid lines are <strong>NOT</strong> necessarily straight over the entire image, so cannot approximate as a grid of straight lines. I am familiar with imageJ or Gatan digitalMicrograph software, if anyone knows of a simple solution. Otherwise matlab/python Opencv would be useful</p>