When a image is subset by the ROI(blue line in the image), some pixels on the boundary was included. However, I want to keep the pixels that completely or a percentage threshold value such 90% of pixel area located within the ROI, which is not contaminated by the boundary objects such as the road. However, I found it difficult to get these pixel through IDL because no ENVI routines supported for this operation. I am also try do this by a simple way. I am removed the pixels of the first and end lines, and also the first and end pixels of other lines to get the center pixels, However, some ROI are over removed, you can see the red pixels after this operation. Can you give me some help?