I could not do it directly from mplay. I tried using ports via imdisplay, but once I load an image into mplay through imdisplay, the mouse selection does not work any more. I think in later versions, you can use ports directly within mplay, but I do not have access to that. I just wanted to know if getting mplay to output those coordinates is possible at all, or am I chasing a lost cause? All suggestions are appreciated, thanks!
PS. As a last resort, I will try doing the region selection in maya, getting the coordinates and feeding those to Houdini, but I am hoping for a slightly more straightforward solution.