Carol,
After your first loop, the image buffer for "Current image" is also the image buffer in "Previous Image". Remember, Vision does not copy buffers for you like most data.
What I would do is use two shift registers. One would hold "Current" and the other would hold "Previous". At the beginning of each loop, acquire a new "Current" image and do the subtraction operation. At the end of each loop, swap the shift registers contents.
If you want to get fancy, you could do the same thing with a single shift register. Add a second terminal on the left hand side. The top terminal is Previous and the bottom terminal is Current. Current goes to the acquire image, and Previous goes straight to the image subtraction. At the end of the loop, Current goes into the shift register terminal on the right. This might be the easiest method, because all you have to do to your current code is add the terminal and route "Current frame" through it.
In both methods, you would need to feed a unique image buffer into each shift register terminal on the left side of the loop.
Bruce
Bruce Ammons
Ammons Engineering
