What I meant about the Greyscale constant is that it's not hooked up to the right place. In cases where you need to create an image, that constant would get hooked up to the image type. In your case, you get the image type from the AVI file. The greyscale is hooked up to the image border (a numeric value which changes the additional pixels around an image, necessary for operations with structuring elements such as the dilate function) , which is best left unconnected unless you have a need to increase it. In your case, I don't believe it matters, I'm simply saying that the constant doesn't have to be there.
To create a destination image, you make a spot in the memory for your image. Use an IMAQ create, give the image a new name, make the type Greyscale (U8), and then hook the image up to the Image DST terminal on the Extract Planes VI (right below the Image SRC, or source, which you've already hooked up). You can create the image outside of the loop, and then wire it inside.
But, there's also a different issue here. The Extract Single Color Plane VI is designed for color images. You said that you have a black and white camera, which would imply that the AVI you've recorded is also black and white. If that's the case, than each frame you're grabbing is already a greyscale image, and the Extract Single Color Plane not only wouldn't work, but it wouldn't make sense (it's designed to convert a color image to greyscale). If the AVI was saved as a U32/Color file, then the program should work properly if you use the destination image as described above. If your AVI was saved as greyscale (which I believe it was), then the extract planes VI should be unnecessary, and you can wire the AVI frame output directly to your detect circles and Caliper VI.
