My IMAQ overlay ROI ' s background become black and not the input image

[PULSE.Wannabe]

Hey, I'm new to machine vision, currently I'm making a project which I use a red object as a control. I use vision assistant to acquire red particles from the cam, then I use overlay rectangle to bound the red object. Then I want to make an output picture where my rectangle overlay with red color overlap with a background picture. But even though the Region (red colored rectangle overlay) appear, my IMAQ overlay ROI ' s background (input image) become black and not the input image I desired. 

Any suggestions are welcome !
thanks in advance

[Gregory · Accepted solution]

Give this knowledge base article a read:
https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000PAovSAG&l=en-US

The image datatype in LabVIEW differs from most others in that it's a reference to a buffer. So if your "Vision Assistant" changes the background to black, it will change the buffer which you have feeding into all of the other displays. If you create a new image (IMAQ Create) and wire to your "Image Dst" input of vision assistant, then the Vision Assistant will not alter your original "pic1" buffer.