You are supposed to set teh Min Thresh Value and Max Thresh Values to whatever you want them to be so that the pixels that end up in your ROI will have values between the Min Thresh Value and Max Thresh Value. The values are used as simple thresholds. There is no equation involved. For example, say that I have an image with pixel values ranging from 0 to 255. I want to make an ROI that includes all of the pixels that have values between 40 and 50. I would set the Min Thresh Value to 40 and the Max Thresh Value to 50. That's it. All pixels with values equal to or between 40 and 50 will end up the ROI that is generated.

hi whammer Thank you very much for you helping, dear whammer i have another problem with how make 3D imag from PRISM data. Thank you very much for your guidance. Sincerely Yours, Hadi Fadaei