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As a first stop. Have you tried using the "External Window" tools. I'm not sure of the details, but I seem to remember some people switching to it for similar reasons. Outside of LabVIEW, I have used Raphael (JavaScript) but had to write my own ROI and annulus which isn't that hard really. Another that springs to mind is ImageJ. This is Java (....shiver....) but has excellent manipulation tools and certainly should be on your list of "things to look at"

I gave some serious thought to the picture control, which is still LV and probably UI thread and cpu demanding. I didn't really went that far, but at least sort of implemented zoom and pixel value indicator, and taxing cpu I get in the 30fps range. Not even nearly as nice as the imaq display, but at least an alternative. It's in my https://lavag.org/files/file/232-lvvideo4linux/