How can I access more information about current Overlays than what IMAQ provides?

[Nokaroa]

I have had a number of difficulties using image overlays on live-camera feeds, and I believe having more access to information about overlays on an image would help me solve many of them. 

I have looked through the provided documentation for the VIs in the Vision Utilities > Overlay group, and there is little to no information about implementation.

Here are a few examples of things I need to know:

1) How many overlays are currently on an image? Where can I access a list to see what currently exists on the image? How can I check if an overlay exists before attempting to clear it? 

- this one is of the highest concern, because I have ran into issues where I believe there were too many overlays being written onto one image. But I had no ability to debug them.

2) How can I access the visible attribute of an overlay without deleting it?

3) Can they be manually moved?

4) How can I store a reference to an overlay? 

These questions might be moot once I know how overlay is implemented, but I can't find any details about that anywhere.

[Zieleslaw · Accepted solution]

1) I never found an option to get overlay information - I just stored "Groups" along with the image reference and manually added / removed them from array, when I overlayed or cleared something from the image. When in doubt - you can use "IMAQ Get Overlay Properties.vi" and a name of a group you want to check - if it doesn't exist, this VI returns an error.

2) What is the "visible attribute" that you mention?

3) Maybe the solution you need is within Overlay Properties - you can decide whether the overlay should be cleared (when no longer valid), transformed along with the image (when the overlay is somehow related to what's in the image) or kept as it is (when it's unrelated to image's content). You can define a different behavior for type of an image transformation. This worked fine for me.

4) This reference is just overlay groups name - a string.

Just like you, I would like to have some more VIs regarding overlay's, but even now you can achieve quite a lot with them ;).