[Greg McKaskle]

I opened the NI Example Finder, under the Help menu, and searched for Straight Edge. If you set the Number of lines to 2 and drag a rectangle around the image, it will locate both the top and bottom lines. You most likely want to use the mechanism in the white paper to find the bounding box of particles, then use the straight edge to get precise fits to the edges.

Again, this will be a bit tedious, your original image had stronger edges between the board and the background than the tape and board. So without a good bounding rectangle, the edge detection may do what you ask and not what you want.

Contours are another way to go with this. The attached image shows the contour and the graph to the right shows the sharp corner transition. You may want to use the bounding box to set the ROI to where you expect each corner to be and process then one at a time, and then recombine.

Greg McKaskle