How to isolate a random shape into roi in ni vision assistant

[PULSE.Wannabe]

I want to find black stuff in the center of white stuff with no exact shape (flour) , but there are many black colored stuff outside the flour area, are there way to isolate only the area of the flour ? I use contour analysis but it didn't detect all the contour.

[raphschru]

It would greatly help if you could share a sample image so we can try some image processing...