Question on transparent image buttons with irregular shape (Captivate 2017)

Hi,

As the title says, I'm using transparent image buttons. I created three .png files, and put _up, _down, and_over at the end of the filenames. I put them into the project, and they work fine. I clicked the Set Transparent box, and the transparent color does not appear. So far, so good.

My question is this: Is it possible to only activate the non-transparent areas of the button? The image I'm using is a map, so the shape is irregular. However, the button activates when I rollover/click anything in the rectangular shape (the image+transparent area). Is there any workaround for this? I want to use several maps that border each other, and the rectangular areas will overlap (which I obviously don't want).

Thanks,

Mike