Using convex hull function for my apple detection and count project

[whistlerfisher]

I am really new to Labview. I am working on an apple detection and count project. It is basically what I have done below.

[whistlerfisher]

The basic algorithm is using HSV threshold to obtain a detectable image, than using the count function in machine vision, as shown in the figures. But it seeming not working. I had tried NI vision assistance, find out the IMAQ convex hull function can make some improvement in the project. But when put the convex hull function in block diagram, the image result is totally black. Really appreciated if any one could help to make it work, or any advice on my projects.